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BJ Services

One Volume

Revision 1.03

22 August 2005

ET-205

TN Densimeter Repair

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BJ Services BJ Services Title BJ Services

ET-205 T

N

D

e

nsimeter R

e

pair

Revision 1.03

ET-205 T

N

D

e

nsimeter R

e

pair

Revision 1.03

ET-205 T

N

D

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nsimeter R

e

pair

Revision 1.03

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Introduction

Definition of Terms

Theory of Operation

Radiation Safety Review

Detector Assembly

BJ Digital Transmitter

Controllers/Data

Acquisition Systems

Specifications and

Conversions

Nuclear Densimeter

Calibration

Nuclear Density

Maintenance

Appendix A

Appendix B

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Proprietary and Confidential Property of BJ Services Company 1

Nuclear Densimeter Introduction

ET-205 Densimeter Repair

BJ Services’ Introduction

BJ Services is an oilfield service company specializing in pressure-pumping and coiled tubing operations. A large part of the pressure pumping services include the cementing and stimulation of wells. These services require a means to measure the density of the various slurries pumped into the well during a given job.

Nuclear Densimeter Introduction

To this end, BJ utilizes the TN Technologies Nuclear Densimeter, which measures the density of a slurry

through radiation detection. This method of measurement works well with both proppant-laden and

cement-laden slurries. This device, however, is extremely sensitive, and the Electronic Technician, or ET, is usually assigned the duty of ensuring the Nuclear Densimeter works properly.

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Proprietary and Confidential Property of BJ Services Company 2

Scope Of This Manual

• Nuclear Densimeter Introduction

• Terminology

• Theory Of Operation

• Radiation Safety Course Review

• Detector Assembly

• Transmitters

• Specifications

• Conversion

• Calibration

• Maintenance

• Troubleshooting

Scope Of This Manual

In order to properly maintain the Nuclear Densimeter, the ET must first understand both Operational and Standardization procedures. The scope of this course, then, can be divided into three main objectives:

• Operation • Standardization

• Duties Of The Electronic Technician Operation

Before an Electronic Technician can perform his required duties for the Nuclear Densimeter, he must first understand its operation (bullet points 1-6), down to the electronic level.

Standardization

With BJ’s acquisition of various oilfield service companies through the years, the issue of

standardization (bullet points 7-8) has increased in importance. The Instrumentation Engineering

department has made the effort to incorporate the “plug n’ play” concept, where if a district borrows a Nuclear Gauge, or any other piece of instrumentation from another district, no modification is necessary. The device is simply hooked up and used for the job. While these various companies use the same Nuclear Technology, there are electronic differences that can make the “plug n’ play” concept difficult to implement. It is the responsibility of the ET to ensure that all Nuclear Densimeters are wired the same way, regardless of company origin.

Duties Of The Electronic Technician

After standardization is achieved, the ET is ready to perform his duties (Bullet Points 9-11). There are calibration and maintenance procedures that the ET must perform in order to ensure that the Densimeter works properly, and when problems occur, he must find the source of the problem and correct it in a timely fashion.

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Proprietary and Confidential Property of BJ Services Company 3

Specifications

• Dimensions (w/o Pipe)

– Length, 13 in (33.0 cm) – Width, 13 in (33.0 cm) – Depth, 30 in (76.2 cm) – Weight, 125 lbs (56 kg)

• Pipe Size

– 2 to 10 in (5.1 to 25.4 cm)

• Operating Temperature

– 40° to 130°F (4° to 54°C)

• Detector Output

– 0 to 10VDC

• Power Requirements

– ±15VDC @ 60mA minimum Specifications

From this point, the operation of the Nuclear Densimeter, or Gauge, is discussed. To begin, the specifications for this device are listed above. They include:

• Dimensions • Pipe Size • Operating Temperature • Detector Output • Power Requirements Pipe Size

The Nuclear Densimeter can be mounted on a wide range of pipe sizes. For BJ Services, this range is from 2 to 10 inches. If the Gauge is removed from one pipe and mounted on another, it must be

re-calibrated. There are however, certain gauges that cannot legally be removed from the pipe. This topic

is discussed in Section 3, Nuclear Densimeter Theory of Operation. Operating Temperature

Specifications list the operating temperature as 40° to 130°F (4° to 54°C). If the Nuclear Densimeter is

operated outside this temperature range, it will still function but its accuracy may be compromised, and its output may become unstable, causing the density reading to fluctuate.

Detector Output

Depending on the density of the fluid circulating through the pipe, the Gauge outputs a 0 to 10VDC non-linear signal.

Power Requirements

The Nuclear Densimeter requires ±15VDC to operate. It receives this power from some type of monitoring electronics, referred to in this course as a Transmitter.

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Proprietary and Confidential Property of BJ Services Company 4 Transmitter TN Nuclear Densimeter 0-10VDC Signal ±15VDC Power

Nuclear Densimeter/Transmitter

TN Nuclear Densimeter/Transmitter Relationship

To receive its needed dual-polarity power, the TN Nuclear Densimeter is typically connected to a transmitter. There are additional functions of the transmitter, which are discussed in Section 3, Nuclear Densimeter Theory of Operation. The slide above shows a Gauge connected to a BJ Digital Transmitter, operating as a Stand Alone Transmitter. In addition to this type of transmitter, there are other devices that possess the capacity to power a Gauge. These include:

• Data Acquisition Systems • Control Systems

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Proprietary and Confidential Property of BJ Services Company 5 TN Analog Transmitter

TN Digital Transmitter

BJ Digital Transmitter

Stand Alone Transmitters

Stand Alone Transmitters

A Stand Alone Transmitter can power the TN Nuclear Densimeter. The various transmitters used by BJS

include:

• TN Analog Transmitter • TN Digital Transmitter • BJ Digital Transmitter

Only the BJ Digital Transmitters will be discussed in detail in this manual. Aliases

Depending on the Company of Origin (i.e., BJ Services, Western, NOWSCO, Fracmaster), the District, or even the individual, these Transmitters are known by various names, including:

• “Analog Head” • “Digital Head” • “BJ Density Module” • “Density Module” • “Density Display” • “Tex. Nuc. Density”

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Proprietary and Confidential Property of BJ Services Company 6 3305 Mini Monitor 3600 Well Treatment Analyzer

Data Acquisition Systems

Data Acquisition System

The primary function of a Data Acquisition System is to monitor and record the processes during a job. In addition to this function, they possess the capacity to power a Nuclear Densimeter. The data

acquisition, or monitoring systems used by BJ include: • 3305 Mini Monitor

• 3600 Well Treatment Analyzer • Isoplex36 Well Treatment Analyzer • Isoplex DAU

Operations Manuals

Each data acquisition system listed has an operations manual available which discusses the connection of a Nuclear Densimeter, therefore they are not covered in this manual. The 3305 Mini Monitor is

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Proprietary and Confidential Property of BJ Services Company 7 Pendant Control System

611C Control System

Control Systems

Control Systems

The primary function of a control system is to regulate the processes of a job. Similar to the data acquisition systems, most control systems have the ability to power a Nuclear Densimeter. These include:

• Pendant Control System (shown above) • 611C Control System (shown above) • Universal Control Module II (UCM II) • Mixing Control Module Series (MCM Series) • Automatic Cement Controller II (ACC II)

The Nuclear Densimeter provides the Operator with a density reading at the controller and, on blenders used in stimulation applications, this density reading from the Gauge can be compared with the density reading calculated from sand-screw rpm's for control purposes.

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Proprietary and Confidential Property of BJ Services Company 8 125C Blender

8” Nuclear Densimeter, Mounted on 125C Blender

Stimulation Applications

Stimulation Applications

When used in stimulation applications, a Nuclear Densimeter is usually mounted at the following locations:

• Blender discharge line (Low Pressure) • The Treating Line (High Pressure) Nuclear Densimeter Mounted On The Blender

A Gauge is mounted on the discharge side of a blender, so that the Operator knows the density of the slurry as it leaves the blender tub. At this point in the process, the slurry is pumped at low-pressure, ranging between 40-100 PSI. The advantage of the low pressure Densimeter is its rapid response to changes in concentration. Once the slurry leaves the blender, it enters the frac pump(s). The photos above show a low pressure Nuclear Densimeter mounted on a 125C blender discharge line.

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Proprietary and Confidential Property of BJ Services Company 9 Nuclear Densimeter, Mounted in the Treating Line

Stimulation Applications

Nuclear Densimeter Mounted In The Treating Line

Once the slurry exits the frac pumps, it travels to the well head under high pressure via the treating line. A Gauge is mounted on a short line (“Pup Joint”) and installed in the treating line in order to monitor the density of the slurry just before it enters into the well head. Pressure in the treating line may approach 15,000 PSI, and in some cases, 20,000 PSI. The photo above shows a Nuclear Densimeter mounted in the treating line. Because the low pressure slurry from the blender may contain some air, thus limiting the accuracy of the low pressure Nuclear Densimeter, the high pressure Densimeter is generally more accurate. Additionally, having two Nuclear Densimeters on the job provides backup insurance and a means for comparison. For these reasons, a high pressure Nuclear Densimeter is normally used on every job.

Additional Application

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Proprietary and Confidential Property of BJ Services Company 10 RAM Cement Unit

Nuclear Densimeter, Mounted on RAM Cement Unit

Cement Applications

Cementing Applications

When used in cementing applications, a Nuclear Densimeter is mounted on cement units (on-shore cement applications), or cement skids (off-shore cement applications). For these applications, the Nuclear Densimeter is usually powered by one of the following:

• Automatic Cement Controller II (Control System) • 3305 Mini Monitor (Data Acquisition System)

• 3600 Well Treatment Analyzer (Data Acquisition System) The Automatic Cement Controller II

When powered by the Automatic Cement Controller II, or ACC II, the Nuclear Densimeter can be used to provide feedback to the ACC II, in order to regulate the cement-mixing process. Additionally, it is possible to serially link the ACC II and the 3305 Mini Monitor so that the density reading can be transmitted to the 3305 for monitoring and recording purposes.

The 3305 Mini Monitor

In some instances, a DB-IV electronic densimeter is used to regulate the cement-mixing process. In this case, the Nuclear Densimeter is powered by a 3305 Mini Monitor and used for monitoring and recording purposes.

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Review Questions

Introduction, Densimeter Repair

Page 1 of 2

1. The Nuclear Densimeter can be mounted on a wide range of pipe sizes. For BJ Services, this range is from 2 to 10 in. If the Gauge is removed from one pipe and mounted on another, it must be ____________________.

2. Specifications list the Operating Temperature as __________° to __________°F (__________° to __________°C).

3. Depending on the Density of the Fluid circulating through the pipe, the Gauge outputs a ____________________ Non-Linear Signal.

4. The Nuclear Densimeter requires ____________________ to operate.

5. When used in Stimulation Applications, a Nuclear Densimeter is usually mounted at the following locations:

• _________________________ (Low Pressure) • _________________________ (High Pressure)

6. The advantage of the Low Pressure Densimeter is its ____________________ to changes in Concentration.

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Review Questions

Introduction, Densimeter Repair

Page 2 of 2 This page intentionally left blank.

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Proprietary and Confidential Property of BJ Services Company 1

Definition Of Terms

Densimeter Repair

Definition Of Terms

The first step an Electronic Technician, or ET, must take toward learning Nuclear Densimeter operation is to understand the associated terminology used by Operations personnel. This is important because, usually, the ET isn’t on location where job problems may occur. When the equipment arrives to the yard, the ET must repair the problem, and the Operator is usually the only person who can tell the ET exactly what happened. The Electronic Technician, however, must be capable of interpreting the necessary information from the Operator. To achieve this goal, this section discusses terminology associated with the Nuclear Densimeter that is used at the operations level.

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Proprietary and Confidential Property of BJ Services Company 2

Definition Of Terms

• Density

• Types Of Density

– Bulk Density

– Absolute Density

• Proppant Concentration

• Specific Gravity

• Density Units for Various Applications

– Stimulation

– Cement

– Sand Control

Definition Of Terms

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Proprietary and Confidential Property of BJ Services Company 3

Density

The density of a material is defined as the ratio of a material’s weight to the volume that it occupies. For example, if a 1-gallon (volume) bucket is completely filled with water, it weighs 8.34 pounds (weight).

Therefore:

Units Of Measurement

For BJ Services’ US Operations, the units of measurement for density are usually expressed in pounds

per gallon, or PPG. For International Operations, the units of measurement for density are expressed in

kilograms per cubic meter (kg/m3), or “kilograms per cube.”

PPG 8.34 Gallon Lbs 8.34 Gallon Pounds 8.34 (Volume) Gallon 1 (Weight) Pounds 8.34 Water Of Density = = = =

Density =

ρρρρ

=

Weight

Volume

Weight

Volume

Density

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Proprietary and Confidential Property of BJ Services Company 4

Bulk Density

14.3 PPG

Absolute Density

22.1 PPG

Example: 20/40 Sand

Types Of Density

Types Of Density

Density can be divided into 2 distinct categories: • Bulk Density

• Absolute Density Bulk Density

Some materials, such as sand, are granular, or powdered in nature. These materials have air pockets between the grains, or particles. The total volume that the material and the air pockets occupy is referred to as bulk volume. Bulk density can then be defined as the ratio of a material’s weight to its bulk

volume.

Absolute Density

Other materials, such as liquids, are continuous in nature. That is to say, there is no air pockets, or voids, in the material. The volume of space that a material occupies, without any air pockets, is referred to as the absolute volume. Absolute density can then be defined as the ratio of a material’s weight to its absolute volume.

Bulk Density Versus Absolute Density

In its natural state, 20/40 sand is a granular material. If a 1-gallon bucket is completely filled with sand, it would weigh 14.3 Pounds, so the bulk density would be 14.3 PPG. If the sand was heated until it melted, it would occupy a smaller space because there are no air pockets present between the grains. If a 1-gallon bucket is completely filled with the melted sand, it would weigh 22.1 pounds, so the absolute density would be 22.1 PPG. The absolute density of 20/40 sand is greater than its bulk density because more of the melted sand can fit in a given volume (1 gallon), than granular sand.

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Proprietary and Confidential Property of BJ Services Company 5 1 Gallon 8.34 Pounds 8.34 PPG .045 Gallon 1.00 Pound 22.1 PPG 1.045 Gallons 9.34 Pounds 9.34 Pounds Slurry

+

Absolute Volume, not Bulk

1.045 Gallons

Slurry Density =

ρρρρ

Slurry

= 8.93 PPG

Absolute Density, not Bulk

Base Fluid

Material

Type

Weight

(Pounds)

Volume

(Gals)

Density

(PPG)

20/40 Sand

Absolute Density

Properties Of Mixtures

When a proppant, such as 20/40 sand, is mixed with a base fluid, such as water, the entire mixture may be thought of as continuous. That is to say, the space between the grains of sand is no longer filled with air, but is filled with fluid. In the case of proppant laden slurries, it is important to use the absolute volume, rather than the bulk volume of the sand when computing the total volume and density of the entire mixture.

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Proprietary and Confidential Property of BJ Services Company 6

Proppant Concentration

Proppant concentration is a measurement of the amount of a material that is contained in a unit volume of a mixture or solution. For BJ Services applications, the amount of sand added to 1-gallon of base fluid is referred to as the proppant concentration. The units for proppant concentration are pounds of sand added, or PSA.

Density/Proppant Concentration Relationship

As the above diagram shows, density is not the same as proppant concentration. Density is expressed in units of pounds per gallon (PPG), while proppant concentration is expressed in units of pounds of sand

added to 1 gallon of base fluid (PSA). These two items, however, are directly related. The following

equation mathematically relates density to proppant concentration:

Keep in mind that the proppant concentration is in units of PSA, and all density measurements are in units of PPG.

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        − = Density Proppant Density Slurry 1 Density Fluid Base -Density Slurry ion Concentrat Proppant 1 Gallon Base Fluid 8.34 PPG .045 Gallon 22.1 PPG 1.045 Gallon 20/40 Sand Slurry

+

Absolute Volume, not Bulk Absolute Density, not Bulk

Proppant Concentration = 1 PSA

Slurry Density = 8.93 PPG

Material

Type

Weight

(Pounds)

Volume

(Gals)

Density

(PPG)

9.34 Pounds 1.045 Gallons 8.34 Pounds 1.00 Pound 9.34 Pounds

Proppant Concentration

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Proprietary and Confidential Property of BJ Services Company 7

Specific Gravity =

σσσσ

=

Material’s Density

Water Density

ρρρρ

Material

ρρρρ

Water

=

σσσσ

Water

=

=

= 1.0 (No Units)

ρρρρ

Water

ρρρρ

Water

8.34 PPG

8.34 PPG

Specific Gravity

Specific Gravity

The specific gravity of a material is the ratio of the material’s density to the density of water, which is

8.34 PPG. Since the units, PPG, are both in the numerator and in the denominator, they cancel, which

means that specific gravity does not have any units associated with it. Specific Gravity Of Water, σσσσWater

To obtain the specific gravity of water, σWater, take the density of water, 8.34 PPG, and ratio it with itself, to obtain a result of 1.0, as mentioned before there are no units.

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Proprietary and Confidential Property of BJ Services Company 8

20/40 Sand Density =

ρρρρ

20/40 Sand

= 22.1 PPG

Water Density =

ρρρρ

Water

= 8.34 PPG

σσσσ

20/40 Sand

=

ρρρρ

20/40 Sand

ρρρρ

Water

22.1 PPG

8.34 PPG

=

= 2.65 (No Units)

Specific Gravity Of 20/40 Sand

Specific Gravity Of 20/40 Sand, σσσσ20/40 Sand

To calculate the specific gravity of 20/40 sand, σ20/40 Sand, take the absolute density of 20/40 sand, 22.1 PPG, and ratio it with the density of water, 8.34 PPG, to obtain a result of 2.65.

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Proprietary and Confidential Property of BJ Services Company 9

Density Units For Various Applications

• Stimulation Applications

– Density

• Pounds Per Gallon, or PPG

– Proppant Concentration

• Pounds Sand Added to 1 Gallon of clean fluid, or PSA • Pounds Proppant Added to 1 Gallon of clean fluid, or PPA

• Cement Applications

– Density

• Pounds Per Gallon, or PPG

• Sand Control Applications

– Proppant Concentration

• Pounds Sand Added to 1 Gallon of clean fluid, or PPG

Density Units For Various Applications

The items above list the units that are used to express density and proppant concentration for the various applications within BJ Services. For both stimulation and cementing applications, the units used for density and proppant concentration are consistent with the units described in this section. In Sand

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Review Questions

Terminology, Densimeter Repair

Page 1 of 1

1. The first step an Electronic Technician, or ET, must take toward learning Nuclear Densimeter Operation is to understand the associated ____________________ used by Operations Personnel.

2. The Density of a material is defined as the Ratio of a material’s

____________________ to the ____________________ that it occupies.

3. For BJ Services’ U.S. Operations, the Units Of Measurement for Density are usually expressed in ____________________. For International Operations, the Units Of Measurement for Density are expressed in ____________________.

4. The ____________________ can then be defined as the Ratio of a material’s Weight to its Bulk Volume.

5. The ____________________ can then be defined as the Ratio of a material’s Weight to its Absolute Volume.

6. In the case of Proppant Laden Slurries, it is important to use the

____________________, rather than the ____________________ of the sand when computing the Total Volume and Density of the entire mixture.

7. In BJ Services, the amount of sand added to 1 unit volume of Base Fluid is referred to as the ______________________________.

8. The units for Proppant Concentration are _________________________

9. The ____________________ of a material is the ratio of the material’s density to the density of water, which is 8.34 Pounds per Gallon.

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Proprietary and Confidential Property of BJ Services Company 1

Nuclear Densimeter Theory Of Operation

ET-205 Densimeter Repair

Theory Of Operation

Now that terminology has been covered, the ET is ready to learn how a Nuclear Densimeter Gauge works. This section provides the ET a general overview of the operation of a Nuclear Gauge.

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Proprietary and Confidential Property of BJ Services Company 2 Radiation Energy process fluid pipe radiation source holder Detector Assembly Transmitter

Main Components

Main Components

The drawing above shows the main components of the Nuclear Densimeter, which includes the: • Radiation Source Holder

• Process Fluid Pipe • Detector Assembly • Transmitter

This section discusses the components in the order listed, since the radiation energy originates at the radiation source holder and interacts with the remaining components in this sequence.

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Proprietary and Confidential Property of BJ Services Company 3 Radiation Energy Lead Filled Housing Cesium 137 finished source 0-10VDC

Radiation Source Holder

Radiation Source Holder

The radiation source holder consists of a protective lead-filled housing and a small Cesium-137 finished source pellet. The housing has a small “window” which serves to focus the radiation beam from the finished source.

Radiation Strengths

Radiation strengths are available in:

• 50 mCi (millicuries) or 1.8 GBq (gigabequerels) • 100 mCi (3.7 GBq)

• 200 mCi (7.5 GBq) Radiation “Window”

Radiation energy is emitted from the finished source uniformly in all directions. Because the source is mounted inside the lead-filled housing, the radiation energy is unable to penetrate the lead walls, and can travel only through a cavity or “window”. The radiation energy collimates into a relatively narrow 12° -13° beam that travels through the process fluid and pipe, which is then received by the Detector

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Proprietary and Confidential Property of BJ Services Company 4 Lead Filled Housing Cesium 137 finished source Cavity shutter

Radiation Source Holder

Radiation Source Holder

The photo above shows a cutout view of a radiation source holder, with a simulated radiation source

installed. Notice the lead-filled housing walls. The Cesium 137 finished source is mounted in the

cavity, as shown. The radiation energy can escape only through the cavity. A stainless steel disc, welded in place, protects the cavity from external contamination.

Shutter

Notice also that this particular radiation source holder has a slide gate, or “shutter” associated with it. When closed, the shutter places lead plates over the cavity, which blocks all radiation. This type of source allows the radiation source holder to be removed by qualified personnel. Shutters are used with radiation source holders that are mounted on process fluid pipes ranging from 5”-8”, typically low pressure applications. Some 4” applications may also use a shuttered source, but this is not common.

NOTE

BJ Services’ personnel DO NOT have the authorization to open the radiation source holder, or to

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Proprietary and Confidential Property of BJ Services Company 5 OFF Position ON Position REF Position

Shutter

Shutter Positions

The shutter, shown above, has three positions associated with it. These are: • The ON Position

• The Off Position

• The Reference, or REF Position

There are some older shutters that only have the ON and OFF Positions. Safety Precautions

The shutter must be locked in the OFF position when:

• Removing the radiation source holder from the process fluid pipe

• Making repairs within close range of the radiation source holder (use long handled brushes and scrapers for cleaning inside the pipe).

• Transporting the Nuclear Densimeter

Additionally, when the shutter is in the ON position, keep others and yourself at least three feet away from the gauge.

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Proprietary and Confidential Property of BJ Services Company 6 Radiation Energy Process Fluid 0-10VDC

Process Fluid Pipe

process fluid

pipe

Process Fluid Pipe

While the radiation energy travels across the process fluid pipe, its magnitude is attenuated, or

weakened, by the process fluid traveling through the pipe. As the density of the process fluid increases, the magnitude of the radiation energy reaching the Detector Assembly decreases.

Empty Process Fluid Pipe

If the process fluid pipe is empty, the radiation energy effectively passes through unmolested (neglecting the radiation attenuated by the process fluid pipe); and reaches the Detector Assembly at what is

considered to be full magnitude. Light Fluid in the Process Fluid Pipe

A light fluid is a fluid with a relatively low density. Water, with a density of 8.34PPG, is a good

example. If water passes through the process fluid pipe, the magnitude of the radiation energy reaching the Detector Assembly is inversely proportional to the water density.

Heavy Fluid in the Process Fluid Pipe

A heavy fluid is a fluid with a relatively high density. Cement and proppant laden slurries are good examples. If a slurry passes through the process fluid pipe, the magnitude of the radiation energy reaching the Detector Assembly is attenuated even further.

TIP

It is important to keep the inside walls of the process fluid pipe as clean as possible. Even a small buildup of sand or cement within the pipe can significantly alter the readings of the Nuclear Densimeter.

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Proprietary and Confidential Property of BJ Services Company 7 Radiation Energy 0-10VDC

Detector Assembly

Detector Assembly Detector Assembly

The Detector Assembly consists of the following major subassemblies: • Ion Chamber

• High Voltage Board • Preamplifier Board

Because there are a number of things that can be done to repair and maintain these components, both the preamplifier board and high voltage board are discussed in detail in this manual. The ion chamber is discussed, but is a sealed component that cannot be repaired by an Electronic Technician. A general overview, however, will be given on all three components.

Role of the Detector Assembly

When properly powered, the ion chamber converts received radiation energy into a proportional current signal that is sent to the preamplifier board; where it is converted and amplified to a proportional voltage

signal of 0 to 10VDC. This non-linear 0 to 10VDC voltage signal is then sent to the Transmitter through a

10-Pin connector.

Density of the Process Fluid

If the process fluid pipe is empty (density = 0.00PPG), then most of the radiation energy reaches the detector assembly. This being the case, the voltage signal sent from the detector assembly is ≈10VDC.

This is referred to as the Open Pipe Voltage, or VOP. If water, with a density of 8.34 PPG, is circulated

through the process fluid pipe, the density increases from 0.00 to 8.34 PPG. Usually, water is used as the base fluid, but other fluids such as brine or KCL may be used as well. The voltage signal generated

while water is circulating through the process fluid pipe is known as the reference voltage, or VREF. As

the density increases, the magnitude of the radiation energy reaching the Detector Assembly decreases. As a result, the voltage signal sent from the Detector Assembly decreases as well.

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Proprietary and Confidential Property of BJ Services Company 8 + -+ + - -+ + + + -Radiation Energy + -+ -Anode Cathode Ion Chamber Filled with Xenon

Gas Positrons Electrons V R ∆∆∆∆V Ion Pair Current Signal

Ion Chamber

Ion Chamber

The Ion Chamber is a cylinder that receives radiation energy and converts it into a proportional electrical signal. The assembly consists of a stainless steel cylinder filled with xenon gas and an insulated center wire. A stable +1400VDC from the high voltage board is applied to the wall (canister) of the ion

chamber. The TN Technologies Densimeter is configured so that the chamber wall acts as an anode and

the wire acts as a cathode. The principle is similar to that of a Geiger Counter, however most Geiger Counters use polarity which is reversed from the above example.

Ion Chamber Operation

Ionization is the process of an atom becoming charged due to its losing or gaining an electron. When the radiation energy enters the ion chamber, it ionizes with the xenon gas, creating ion pairs. Each ion pair consists of:

• A Negative Ion (also known as an Electron) • A Positive Ion (also known as a Positron)

The positrons are drawn to the wall of ion chamber, while the faster moving electrons are drawn to the wire. A charge collects on the Anode, resulting in a voltage change in the circuit. The size of this voltage change depends on the number of electrons collected from the ionizing process. This causes a proportional current signal to flow to the preamplifier board, where it is then converted to a voltage signal and amplified to 0 to 10VDC.

Radiation Energy/Ionizing Relationship

If the full magnitude of the radiation energy enters ion chamber, a greater number of ion pairs are created, and more charge collects on the anode, resulting in a larger current signal. This larger current signal results in a larger voltage signal sent to a transmitter, ideally 10VDC, or VOP. If the magnitude of the radiation energy entering the ion chamber is attenuated, the number of ion pairs created is less, which results in a smaller current signal, resulting in a smaller voltage signal sent to the transmitter.

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Proprietary and Confidential Property of BJ Services Company 9 high voltage board preamplifier board Ionization Chamber Lead Shield

Detector Assembly

Detector Assembly

The photo above shows the detector assembly. The high voltage board is mounted above the ion chamber. The lead shield, mounted on the top plate, blocks radiation from passing through the signal/power connector. This shield might not be found on new units.

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Proprietary and Confidential Property of BJ Services Company 10 Radiation Energy 0-10VDC ±15VDC

Transmitter

Transmitter Transmitter

A transmitter provides four important functions: • Linearizes the 0-10VDC density signal • Displays the density

• Supplies the Nuclear Densimeter with ±15VDC

• Transmits the density signal to a remote monitor via frequency signals, analog signals or digital communication.

A transmitter linearizes the voltage signal from the Detector Assembly and produces a numerical value, which is indicative of the density for the process fluid. Additionally, it provides a display of the density for the Operator.

Proppant Concentration

In stimulation operations, the transmitter also calculates the proppant concentration in the fluid. Proppant concentration is measured in units of PSA, or Pounds Sand Added.

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Proprietary and Confidential Property of BJ Services Company 11 3305 Mini Monitor 3600 Well Treatment Analyzer Pendant Control System

Analog Transmitter Digital Transmitter TN Nuclear Transmitter

Transmitters

Transmitters

There are a number of devices that may be utilized, in whole or part, as a Transmitter. • TN Analog Transmitter

• TN Digital Transmitter • BJ Digital Transmitter • 3305 Mini Monitor

• 3600/Isoplex36 Well Treatment Analyzer • Pendant Control System

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Proprietary and Confidential Property of BJ Services Company 12 Radiation

Energy

0-10VDC

Nuclear Densimeter Review

process fluid pipe radiation source holder Detector Assembly Transmitter

Nuclear Densimeter Review

The Nuclear Densimeter consists of four main components: • Radiation Source Holder

• Process Fluid Pipe • Detector Assembly • Transmitter

The radiation source holder emits radiation energy through the process fluid pipe. Depending on the density of the process fluid passing through the pipe, the proportional magnitude of the radiation energy is received by the Detector Assembly, where it is converted to a 0-10VDC non-linear signal. This signal is passed on to the transmitter, where the voltage signal is linearized, converted into a density reading, displayed for the Operator, and made available for a remote monitor.

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Review Questions

Theory of Operation, Densimeter Repair

Page 1 of 2

1. The Radiation Source Holder consists of a protective

______________________________ and a small ____________________ Finished Source pellet. The housing has a small ____________________ which serves to focus the radiation beam from Finished Source.

2. BJ Services Personnel ____________________ have the authorization to open the Radiation Source Holder, or to remove a non-shuttered Source from the pipe. 3. Additionally, when the Shutter is in the ON position, stay at least

____________________ away and keep others away from the gauge.

4. As the Density of the Process Fluid ____________________, the magnitude of the radiation energy reaching the Detector Assembly ____________________.

5. It important to keep the _________________________of the Process Fluid Pipe as clean as possible. Even a small buildup of sand or cement within the pipe can significantly alter the readings of the Nuclear Densimeter.

6. When properly powered, the ____________________ converts received radiation energy into a proportional Current Signal and sends it to the Preamplifier Board 7. If the Process Fluid Pipe is empty (Density = 0.00PPG), the ____________________

of the radiation energy reaches the Detector Assembly.

8. When the radiation energy enters the Ion Chamber, it ionizes with the Xenon Gas, creating ____________________.

9. The ____________________ linearizes the Voltage Signal from the Detector

Assembly and produces a numerical value, which is indicative of the Density for the Process Fluid. Additionally, it provides a display of the Density for the Operator.

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Review Questions

Theory of Operation, Densimeter Repair

Page 2 of 2 This page intentionally left blank.

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Proprietary and Confidential Property of BJ Services Company 1

Radiation Safety Review

ET-205 Densimeter Repair

Radiation Safety Review

So far in this presentation, the Nuclear Densimeter has been discussed on a general level. In the sections to follow, a more in depth discussion is given, which involves opening the Detector assembly, calibration and troubleshooting. Whenever working around a device that is radioactive, safety must always be a top priority for the ET and personnel in the area. Before going forward, a review of the Radiation Safety Course is given in this section.

Radiation Safety Course

The purpose of the Radiation Safety Course, offered by TN Technologies, is to provide personnel with a general understanding of the possible hazards associated with Nuclear Densimeters. Additionally, the course explains how to work confidently and safely around this device.

A Prerequisite

This section is intended only as a supplement to the Radiation Safety Course offered by TN Technologies. Before an Electronic Technician can handle/repair a Nuclear Densimeter, he must

successfully complete the Radiation Safety Course. This is necessary due to the potential hazards if the Densimeter is handled incorrectly.

Topics of Discussion

The following topics are discussed in this section: • What is Radiation

• Using Radiation Safely

• BJ Services Radiation Protection Manual • Labels

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Proprietary and Confidential Property of BJ Services Company 2

What Is Radiation?

• Alpha Radiation

• Beta Radiation

• Gamma Radiation

• X-Ray Radiation

• Neutron Radiation

What Is Radiation?

In order to work safely around Nuclear Gauges, one must first understand some basic facts about radiation. Radiation originates from atoms, which are the building blocks of all matter. Certain atoms

are at excited states and release energy in the form of radiation. This energy is transferred as either

particles or electromagnetic waves. Types Of Ionizing Radiation

There are 5 types of Ionizing Radiation: • Alpha Radiation

• Beta Radiation • Gamma Radiation • X-Ray Radiation • Neutron Radiation

Each has a unique penetrating ability that needs to be considered when protecting oneself from Radiation.

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Proprietary and Confidential Property of BJ Services Company 3

What Is Radiation?

• Alpha Radiation

• Beta Radiation

• Gamma Radiation

• X-Ray Radiation

• Neutron Radiation

Alpha Radiation

Alpha radiation occurs when the atom emits large atomic particles. These particles have very little external penetrating power, and can be shielded with something as thin as a piece of paper. When exposed externally to Alpha radiation, it poses no external hazard because it can be shielded by the dead

layer of skin covering the body. Alpha radiation, however, can be internally harmful if inhaled or

ingested. Beta Radiation

Beta radiation occurs when the atom emits small, fast moving particles known as electrons. These particles are more penetrating than Alpha particles, but are still considered to have relatively low penetrating ability. Beta radiation can be easily shielded by materials such as cardboard or plastic. It can, however, penetrate the dead layer of skin on the body.

Gamma Radiation

Gamma radiation occurs when electromagnetic waves are emitted from an atom as a result of radioactive decay. This form of radiation has a high penetrating ability, and is considered an external threat.

Gamma radiation can be shielded by a dense material such as concrete or lead.

X-Ray Radiation

X-Ray radiation is similar to Gamma radiation in that it emits electromagnetic waves. X-Ray radiation, however, is generally machine generated and is less penetrating than Gamma radiation.

Neutron Radiation

Neutron radiation results from the emission of a Neutron particle from the nuclei of an atom. This form of radiation is extremely penetrating and poses a significant external threat.

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Proprietary and Confidential Property of BJ Services Company 4

Exposure vs. Contamination

What Is Radiation?

Exposure vs. Contamination

Many people have the misconception that if they become exposed to radiation, that they will glow in the dark, and become radioactive themselves. This, of course, is incorrect. A good way to explain what actually occurs is through using the fire analogy.

Exposure

If an extremely intense fire is a very short distance away, the heat from the fire may result in burns to the body. However, the farther the distance from the fire results in less heat exposure, which causes less damage to the body. The same concept can be related to Exposure. The more time spent around a radioactive source, and the closer the distance to the source, a greater Exposure results.

Contamination

After leaving the vicinity of a fire, the person does not emit heat unless he brings an amber from the fire.

Similar to contamination, a person must physically come in contact with, and take a portion of the radioactive material to become contaminated, or radioactive.

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Proprietary and Confidential Property of BJ Services Company 5

A

L

A

R

A

s

ow

s

easonably

chievable

Using Radiation Safely

Safety Factors

The different types of ionizing radiation are harmful, but there is a very little risk associated with the

low levels of radiation of a Nuclear Densimeter. Nevertheless, in practice a person should keep his

exposure As Low As Reasonably Achievable, or ALARA. This can be done by following 3 simple

concepts: • Time • Distance • Shielding Time

The more Time one remains in a radiation field, the larger the radiation dose. At times, especially during

emergencies, work must be performed in a strong radiation field. In this case, the work procedure should be carefully planned outside the work area so that a minimum amount of Time is used to complete the job. If the Time required for one man to complete the job would result in an exposure beyond prescribed

limits, then a team of workers should be employed. This would mean a small exposure for several

people instead of a large exposure for one person. Distance

Radiation is emitted from a point source uniformly in all directions. The further one is from the radiation source, the lower the exposure.

Shielding

A Shield is defined as a physical entity placed between the radiation source and the object to be

protected in order to reduce the radiation level at the object’s location. An example would be the

radiation source holder. The radiation source is mounted within a lead-filled housing that prevents the Radiation from traveling anywhere except in the specified direction. In this case, the physical entity is the lead filled-housing, and the objects to be protected are BJS personnel.

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Proprietary and Confidential Property of BJ Services Company 6

BJ Services Radiation Protection Manual

• Emergency Instructions

• Radiation Program Management Organization

• Radioactive Materials Records Management

• Radioactive Materials - Employee Notices and

Instructions

• Use of Densimeters Having Nuclear Gauges

• Transportation Procedures

• Handling Procedures

• Radiation Protection Program Review

• Nuclear Gauge Procedures

BJ Services Radiation Protection Manual

The Nuclear Regulatory Commission, and equivalent Agreement States have strict safety standards for Nuclear Densimeters. These strict regulations for radioactive material provide a high degree of worker and environmental safety when dealing with radiation. Each state, or country, operates under a specific radioactive materials license or a manufacturer’s general license. Individuals operating Nuclear

Densimeters should be aware of the license conditions and follow them accordingly. There are,

however, BJ specific regulations that must be followed regardless of state, or country, which are listed in

the BJ Services Radiation Protection Manual. The topics in this manual include:

• Emergency Instructions

• Radiation Program Management Organization • Radioactive Materials Records Management

• Radioactive Materials - Employee Notices and Instructions • Use of Densimeters having Nuclear Gauges

• Transportation Procedures • Handling Procedures

• Radiation Protection Program Review • Nuclear Gauge Procedures

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Proprietary and Confidential Property of BJ Services Company 7 CAUTION RADIOACTIVE MATERIAL ISOTOPE AMOUNT DATE MEAS. MODEL SERIAL NO.

Texas Nuclear Products

TN Technologies

DO NOT REMOVE TAG

MADE IN USA 5190 BXXX Cs-137 EMPTY 09/97 BJ DEMO TAG NO.

Labels

Radiation Source Holder Plaque

The Radiation Source Holder Plaque, which provides information about the finished source, is mounted on the end of the Radiation Source Holder. When installing or removing a Nuclear Gauge, be careful not to drag the Radiation Source Holder on the ground, as this could destroy the information on the plaque, resulting in a loss of critical information.

Missing Or Illegible Plaque

Missing or illegible plaques must be replaced immediately. These plaques must be ordered through the manufacturer. A missing or illegible plaque renders the device out of service until a replacement plaque is mounted.

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Proprietary and Confidential Property of BJ Services Company 8

R

A

D

IO

A

C

TIV

E

II

CO N TEN TS : C E SIU M 1 37 AC TIVIT Y :

7

TR ANS POR T IN DE X RAY II Label

R

A

D

IO

A

C

TIV

E

II

C O N TEN TS : C ES IU M 1 37 AC TIVIT Y:

7

TR ANS POR T IN DE X RAY II Label

USA DOT 7A

TYPE A

RADIOACTIVE

MATERIAL

SPECIAL FORM, N.O.S., UN 2974 (CS-137; SEALED)

Notify if found: BJ SERVICES CO., USA

HOUSTON, TEXAS

Emergency RSO contact: (281) 351-8131 24 hour

Marking Label

Labels

Labels

To comply with the licensing agreement, every Nuclear Density Gauge must have two Radioactive

Yellow II Labels (RAY II Labels) and one Marking Label. Radioactive Yellow II Labels (RAY II Labels)

The 2 Radiation Yellow II, RAY II, Labels must be placed on the Radiation Source Holder on opposite sides. A RAY II Label displays the following information:

• Contents (Always Cesium 137 for BJ Services) • Activity (In Gigabecquerels, GBq)

• Transport Index

This activity can be obtained from the AMOUNT reading on the Radiation Source Holder Plaque. The AMOUNT value is expressed in units of millicuries, so a unit conversion is necessary. (100mCi = 3.7GBq and 200mCi = 7.4 GBq).

Transport Index

When transporting the Nuclear Densimeter, the TRANSPORT INDEX must be filled in. This value is determined by taking the highest radiation survey meter reading at any point 1 meter (39 inches) from any surface of the Radiation Source Holder. The value must be less than 1.0 (no units necessary) to use the RAY II Label. The Transport Index is written to the nearest tenth (Example: use 0.3, not 0.25). Marking Label

The Marking Label must be placed between the RAY II Labels. A Marking Label displays the following information:

• USA DOT 7A type A Radioactive Material • Emergency phone number

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Review Questions

Radiation Safety Review, Densimeter Repair

Page 1 of 2

1. Radiation originates from ____________________, which are the building blocks of all matter.

2. When exposed externally to _________________________, it poses no external hazard because it can be shielded by the dead layer of skin covering the body.

3. _________________________ can be easily shielded by materials such as cardboard or plastic.

4. ____________________ Radiation has a high penetrating ability, and is considered an external threat. Gamma Radiation can be shielded by a dense material such as concrete or lead.

5. The more time spent around a radioactive source, and the closer the distance to the source, a greater ____________________ results.

6. A person must physically come in contact with, and take a portion of the radioactive material to become ____________________

7. A ____________________ is defined as a physical entity placed between the

Radiation Source and the object to be protected in order to reduce the Radiation Level at the object’s location.

8. The ______________________________, which provides information about the Finished Source, is mounted on top of the Radiation Source Holder.

9. The 2 Radiation Yellow II, RAY II, Labels must be placed on the _________________________ on opposite sides.

10. When transporting the Nuclear Densimeter, the ______________________________ must be filled in. This value is determined by taking the highest radiation survey meter reading at any point 1 meter (39 inches) from any surface of the Radiation Source Holder.

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Review Questions

Radiation Safety Review, Densimeter Repair

Page 2 of 2 This page intentionally left blank.

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Proprietary and Confidential Property of BJ Services Company 1

Detector Assembly

ET-205 Densimeter Repair

Radiation Energy

Detector Assembly

Nuclear Densimeter

The “Fast Start Up” (FSU) detector is an improved version of the early SGO detector. This section of the presentation will deal with the theory of operation and maintenance of the FSU. The following will be discussed in this section:

• General theory of operation review • FSU and SGO Gauge comparisons

• High Voltage and Preamplifier Board circuit detail • Calibration and adjustments

• Maintenance and Troubleshooting Procedures

Note

Only personnel who have successfully completed an approved Nuclear Safety Course are permitted to service nuclear densimeter systems.

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Proprietary and Confidential Property of BJ Services Company 2 Ionization Chamber High Voltage Board Preamplifier Board

Detector Assembly

Densimeter Detector Assembly

The above photo shows a Detector Assembly, also known as an FSU Gauge. The primary subassemblies that make up the FSU Gauge are:

• Ionization Chamber, or Ion Chamber • High Voltage Board

• Preamplifier Board Types of Detector Assemblies

BJ has used two types of TN Technologies Gauges: • TN SGO Gauge (Obsolete)

• TN FSU Gauge

NOTE

Several activities using a Detector Assembly and simulated nuclear sources will be performed in the class. Because there may be residual high voltage present after power is removed, be careful not touch the Ion Chamber when removing it from the housing. To discharge the residual voltage, first connect a jumper to one of the grounded aluminum plates separating the boards. Next, touch the other end of the jumper to the body of the Ion Chamber.

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Proprietary and Confidential Property of BJ Services Company 3 + 1400 V

Gain

(For Analog Transmitter Only) Ion Chamber Preamplifier Board High Voltage Board GND -15V +15V GND -15V +15V 0-10V Power From Transmitter Density Signal To Transmitter

Nuclear Densimeter Block Diagram

Radiation Energy

Nuclear Densimeter Block Diagram

The diagram above shows how the components of the Detector Assembly connect. Ion Chamber

The Ion Chamber consists of a stainless steel canister filled with Xenon gas at eight atmospheres. An

insulated wire is inserted into the chamber, and high voltage potential is applied across the anode and cathode. Radiation energy received from the radiation source causes a release of free electrons from the gas. These electrons are attracted to the anode, which creates a small current flow into the preamplifier.

Preamplifier Board

The preamplifier board converts and amplifies this current flow into a voltage signal that is inversely proportional to the density of the material in the path of the radiation energy.

High Voltage Board

The high voltage board supplies a highly regulated +1400VDC, which allows sufficient voltage difference for the attraction of the free electrons.

Power Source

The Nuclear Densimeter is powered from an external ±15VDC, which is supplied by a transmitter or other suitable power supply.

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Proprietary and Confidential Property of BJ Services Company 4 + -+ + - -+ + + +

-Ion Chamber

Radiation Energy + -+ -Anode Cathode + 1400 V Current Flow Ion Chamber

Gamma particles from the nuclear source striking xenon gas ions cause ionization to occur, which results in a current flow. This extremely small current flow is converted by the preamplifier board into a representative 0 to 10VDC density signal.

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Proprietary and Confidential Property of BJ Services Company 5

Adhesive From Heater Wrapping

Ion Chamber

Modified Gauge

The adhesive residue in the above photo identifies this Ion Chamber as part of a former SGO assembly. Due to the inherent sensitivity of the obsolete SGO Gauge to changes in temperature, a heater was taped to the Ion Chamber in order to maintain a constant temperature inside the housing. Additionally, heater resistors on the top plate kept the electronics warm. Because of this temperature sensitivity, the SGO Gauge required long a “warm up” time before the density readings would stabilize, usually about an hour or more in cold climates. Upgrading an SGO unit consists of replacing the two boards and removing the heater.

The FSU Gauge

The improved FSU Gauge contains temperature stabilization circuitry that enables it to remain remarkably stable over a wide range of temperatures. Additionally, the “warm up” time from initial power up is dramatically reduced to 15 minutes or less.

High Voltage To Ion Chamber

There is a +1400VDC potential applied to the Ion Chamber. Although the actual measured voltage has a

±100V tolerance, it must be well-regulated, because any fluctuation, no matter how slight, will cause a

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Proprietary and Confidential Property of BJ Services Company 6

Drain Wire

Insulated Collar

FSU High Voltage Board

High Voltage Board

The high voltage board provides the potential necessary for ionization to occur. This voltage must be

well regulated, as any fluctuation will result in a corresponding signal output change. The board uses

±15VDC, supplied by an external power source, for conversion to +1400VDC at approximately 20 µA.

The output voltage may be within ±100V of the specified voltage, but should have no measurable

fluctuation. In the photo shown, notice the Drain Wire, separated from the Ion Chamber by an Insulated

Collar. This combination is used to drain any static voltage, and to act as an electrostatic shield for the signal current, thereby reducing noise pickup. The signal output current from the Ion Chamber is very small, in the order of nano amps (nA), so even minimal electrical interference can cause large errors in the output signal.

High Voltage Probe

A high voltage probe should ALWAYS be used to measure the potential on the Ion Chamber. Most

modern digital volt meters will read only to 1000V, but this is not the only reason to use a high voltage probe. Because the high voltage board can supply only 20 µA, if a conventional digital multimeter alone were used for measurement the meter’s internal resistance (typically 10 M Ω) would drain much of the available current from the power supply, resulting in a erroneous reading. An example of a suitable probe for high voltage use is the Fluke model 80K-40 High Voltage Probe, which is useful for readings up to 40 kV, at a 1000 to 1 division ratio. Using this or a similar probe, 1400VDC will be displayed as 1.400VDC on a DVM. These high voltage measurements are made from power ground to the Ion

Chamber Canister, with the aluminum plates separating the boards providing a convenient ground point.

NOTE

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Proprietary and Confidential Property of BJ Services Company 7

HV Connection

Screws

High Voltage Board/Ion Chamber Connection

High Voltage Board/Ion Chamber Connection

The three screws that secure the high voltage board to the Ion Chamber also provide the electrical path for the 1400VDC to the Ion Chamber canister. It is important that these screws be properly tightened and

free from corrosion. Removable thread lock, such as Locktite® Green or Red, is recommended.

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Proprietary and Confidential Property of BJ Services Company 8 Blue (-15V)

White/Gray Stripe (Ground) White/Purple Stripe (+15V) U-2 Q-1 U-3 C A 3240 2N3906 MC-79L 12 ACP 3 2 1 T1 From Preamplifier Board -12V Regulator HV Transformer Oscillator

FSU High Voltage Board

CR-1

CR-2

High Voltage Board Layout

Some of the major components found on the high voltage board are illustrated in this drawing. They include:

• High Voltage Transformer, T1 • Negative Voltage Regulator IC, U2 • Oscillator Transistor, Q1

• Control IC, U3

• Rectifier and Voltage Doubler, CR1 and CR2

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Proprietary and Confidential Property of BJ Services Company 9 -12V Regulator Rectifier & Voltage Doubler U3A U3B

±±±±15V Oscillator +1400V(To Ion Chamber)

Voltage Regulation & Filtering

High Voltage Block Diagram

High Voltage Operational Block Diagram

The high voltage circuit consists of a DC/DC converter that uses active voltage feedback for both regulation and dynamic filtering of the output voltage. Major circuits on this board include:

• Free-running LC sine wave oscillator • Voltage regulator IC

• Step-up power transformer • Voltage Doubler circuit

• Active feedback voltage regulation These circuits will be discussed shortly. High Voltage Operation

High voltage for the ion chamber is generated by a free running oscillator circuit, using a step up transformer, along with active feedback to maintain constant voltage under varying loads.

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Proprietary and Confidential Property of BJ Services Company 10

Fusible Resistors

High Voltage Board Power Input

The high voltage board power input is protected using 10Ω, 1/4 watt resistors on the input power. If found to be open, the cause of the short should be repaired and “flame proof” resistors installed.

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Proprietary and Confidential Property of BJ Services Company 11

FSU High Voltage Board

Oscillator -12V Regulator Voltage Doubler Active HV Regulation HV Out Oscillator Circuit

Components Q1, T1, C5, C6, R4, and R5 form an LC Hartley oscillator, utilizing positive feedback to make up a frequency-selective network running at approximately 1.5 kHz. The two primary windings of

T1 act as the inductive portion of the sine wave oscillator. This loop is designed to have a gain of unity at a single frequency as determined by the frequency-selective network. In this type of oscillator, sine waves are generated essentially by a resonance phenomenon. Excitation voltage is supplied by the same ±15VDC that powers the preamplifier board.

High Voltage

The AC voltage produced by the oscillator circuit is stepped up by transformer, T1, to approximately 500VAC (RMS). Half-wave rectification, via CR2, gives a DC voltage of +700VDCwhich is increased to

1400V using a voltage doubler circuit, consisting of C7 and CR1. Filtering is provided by an RC circuit

consisting of C8, R6, R7, C9 and C11. Active (dynamic) filtering is also provided in the feedback circuit.

High Voltage Regulation

Regulation is developed from the voltage value derived from voltage divider R8, R11 and the regulated

-12V from IC, U2. Any deviation is fed back to the oscillator for correction to its output. For this voltage

correction to occur, operational amplifier, U3A, must amplify any deviation between the voltage divider and ground. The non-inverting buffer, U3B, feeds the error voltage to the primary supply voltage for Q1, varying it to hold the output at a constant value. An RC circuit, consisting of R12 and C13, slows the correction slightly in order to prevent overcorrecting, which will cause “hunting”.

Dynamic Filtering

Similarly, any ripple voltage is treated as deviation from the referenced voltage. Amplified ripple voltage from the secondary is fed back through the low side of T1 to null the output ripple, thereby providing dynamic filtering.

References

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