Set Pressure Automatically

To set the measurement mode (absolute, gauge or negative gauge) for the active range.  PRINCIPLE

PPC4E supports simple, one-step switching between up to three different measurement modes:

Absolute Measures pressure relative to vacuum (zero is hard vacuum). Range is from zero absolute to full scale.

Gauge Measures pressure relative to atmosphere, ATM (zero is ambient pressure). Range is from zero gauge to full scale, full scale must be greater than zero.

Negative gauge Measures pressure relative to atmosphere, ATM (zero is ambient pressure). Values are positive and negative, with ranges from negative one atmosphere (-ATM) to positive full scale. If the full scale is less than +ATM, the range is defined from the negative equivalent of positive full scale to positive full scale (for example, -10 kPa to 10 kPa gauge).

When changing measurement modes for a range, if the full scale of the range is 700 kPa (100 psi) or greater, the full scale is the same in both absolute and gauge modes. If the full scale is less than 700 kPa (100 psi), the gauge mode full scale is 100 kPa (14.5 psi) lower than the absolute mode full scale. Gauge and negative gauge mode, when available, have the same full scale.

Note

• Certain PPC4E settings are range AND measurement mode specific. See Table 5 for a listing of settings and what they are specific to.

• Absolute and negative gauge modes can be turned OFF in the calibration function (see Section 0). When absolute and negative gauge mode are turned OFF, only gauge mode can be activated.

 OPERATION

See Section 4.7.6.2.

3.2.11 Set Pressure Automatically

 PURPOSE

To use the automated pressure control functions of PPC4E to set and maintain target pressure values.  opens the target screen to initiate the sequence.

Note

• A target pressure entry that exceeds the current upper limit (see Section 3.2.20) or that is out of range will not be accepted as the target value.

• If PPC4E is unable to control pressure or appears to control pressure poorly, see Section 7 to troubleshoot.

• For PPC4E to set pressures under atmosphere and/or to reliably set pressures under 20 kPa (3 psi) gauge other than zero gauge, a vacuum

pump must be connected to the EXHAUST port (see Section 2.3.5) and PPC4E must be set up for control using a vacuum reference (see Section 3.2.25.2). Setting zero gauge pressure does not require a vacuum.

• The  and  direct pressure control keys can be used while controlling to jog the pressure control target value up or down by the jog step value (see Section 3.2.19). These keys also jog the target value when in the ENTER target value screen.

• Due to the manner in which PPC4E handles an automated pressure command for zero in absolute pressure measurement mode, a

Ready condition can occur at a pressure well outside of the hold

limit. When setting zero in absolute measurement mode, the Ready condition should NOT be interpreted as meaning that the pressure is zero within the hold limit. Ready is an indication that the rate of change of pressure inside PPC4E has reached the current stability limit. The current pressure measured by PPC4E, not zero, should be used as the value of pressure applied to the device or system under test.

• When PPC4E is given a command to set zero in absolute measurement mode, the rate of change of pressure will decrease as the pressure decreases and the rate will eventually be near zero when the vacuum pump has pulled down the pressure in the PPC4E and the test volume as far as possible. To make best use of the Ready/Not

Ready indication when setting zero in absolute measurement mode,

set the stability limit (see Section 3.2.3) to a value that represents the rate of change of pressure expected when the vacuum pump connected to the EXHAUST port has reduced pressure as far as possible.

 OPERATION

See Section 4.5.1.

3.2.12 Control

 PURPOSE

To set the automated pressure control mode for the active range, customize control parameters, activate default control parameters.

 PRINCIPLE

The Control function allows the active control mode for the current range to be set to either dynamic or static. The control mode set is specific to the active range and is saved with that range when ranges are changed. For a complete description of the operation and purpose of static and dynamic control modes see Section 3.2.2.

When a control mode is selected using the Control function, Control parameters are automatically set to default values for the active range (see Table 7 for definition of PPC4E default control parameters). The default control parameters have been determined to be most suitable for the typical user to operate within PPC4E pressure control and measurement specifications. Each PPC4E default range has default control parameters and AutoRange automatically sets control parameters appropriate for the AutoRange range.

Control mode parameters can be viewed and customized in the Control function (see Section 4.7.8). Customizing the hold and/or stability control parameters changes the conditions required for a Ready condition to occur (see Section 3.2.3). This can be used to increase control speed (reduce time to Ready), usually by decreasing control precision, or to increase precision which usually decreases control speed. For example, changing the dynamic pressure control hold limit from its default value of ± 100 ppm of the active range to ± 200 ppm of the active range will decrease the time required to set a pressure since the limit within which the pressure must be set has increased. However, it will also increase the maximum possible control error when Ready is indicated.

Table 7. Default Pressure Control Parameters!!!

STATIC MODE DYNAMIC MODE

HOLD LIMIT

± 1 % of range span or 5 ppm of RPT span whichever is greater

± 100 ppm of AutoRange span or 10 ppm of active RPT span whichever is greater

STABILITY LIMIT

50 ppm of range span or 2 ppm of active RPT span, per second, whichever is greater

50 ppm of range span or 5 ppm of active RPT span, per second, whichever is greater

 OPERATION

See Section 4.7.8.

3.2.13 Vent

 PURPOSE

The  control key activates a sequence to bring the test pressure to atmosphere.  PRINCIPLE

The Vent sequence controls the pressure to near atmospheric pressure then opens the system vent valve (see Figure 18). In addition to bringing the PPC4E test pressure to atmospheric pressure, the Vent sequence also opens the RPT bypass valve for the Hi RPT on PPC4E 15K or Lo RPT on PPC4EX 100K, and after a delay, closes the control bypass valve to minimize consumption of supply gas through the control circuit (See. Figure 17) During the Vent sequence the RED Vent indication is blinking. Once the RED Vent indicator is lighted and steady and the Ready/Not Ready indicator becomes GREEN then the system is fully vented.

 OPERATION

See Section 4.5.3.

3.2.14 AutoTest

 PURPOSE

To execute a programmed sequence of automated pressure control target values.  PRINCIPLE

The AutoTest function is intended to facilitate the execution of a series of pressure control target values such as when PPC4E is used to run a calibration sequence on a device or system being tested.

There are three sequence choices for AutoTest:

Exercise Cycle the Test Pressure between atmosphere or vacuum and a

maximum target pressure such as when exercising a UUT prior to calibration.

The information to the right of Exercise: in the AutoTest menu is the last executed exercise sequence, pressure range and number of cycles.

Quick Test Allows quick definition and execution of a sequence in the current range and using all of the current settings (pressure unit of measure, measurement mode, control mode, control settings, display resolution). The information to the right of Quick Test: in the AutoTest menu is the step size and direction for the last executed Quick Test.

Advanced Test AutoRanges PPC4E based on the full scale and tolerance of a device

under test, prompts the user through the increments of a calibration sequence and logs calibration data. The Advanced Test function allows for the pressure at each target point to be adjusted so that the device under test reads a cardinal target pressure point. This is particularly useful when calibrating analog gauges.

The information to the right of Advanced Test: in the AutoTest menu is the number of saved tests available for selection.

In both the Quick Test and the Advanced Test, the PPC4E records the value of the PPC4E pressure at the time  is used to advance to the next test point. Following the completion of the test the PPC4E values for all of the test points are displayed in a list. If the user is calibrating an analogue device, such as a gauge, the user can adjust the PPC4E pressure to set cardinal points on the analogue device before advancing to the next pressure. If this is done, the list of pressures at the conclusion of the test is the list of PPC4E pressures corresponding to the analogue cardinal points.

 OPERATION

See Section 4.7.2.

3.2.15 Head

 PURPOSE

To cause a pressure fluid head correction to be added or subtracted to the pressure measured by the PPC4E reference pressure transducer in order to predict the pressure at a height other than the PPC4E’s reference level.

 PRINCIPLE

PPC4E measures gauge or absolute pressure at the height of the rear panel TEST(+) port. Frequently, when performing a calibration or test, the device or system under test is at a different height than the PPC4E’s TEST(+) port. This difference in height, frequently called

head height or head, can cause a significant difference between the pressure measured by the PPC4E at its TEST port height and the pressure actually applied to the device under test which is at a different height. In this case, it is useful to make a head correction to the pressure measured by the PPC4E in order to predict the pressure actually applied at a different height.

PPC4E can calculate head pressures for nitrogen, helium and air as the test gas over its working pressure range. The HEAD function allows the height difference to be specified and causes the resulting head pressure to be added to the pressure measured at the TEST port.

The reference height of the PPC4E pressure measurement is the middle of the PPC4E TEST port. The head height should be entered as a positive value if the device or system under test is higher than the PPC4E and negative if it is lower.

Note

• Use of the Head function to ensure in tolerance measurements is most important in low absolute pressure ranges. Specifying the head height within ± 3 in. (± 7.5 cm) is adequate to ensure that, even in the worst case, the uncertainty on the head correction will be insignificant relative to the tolerance on the measurement.

• The Head function is NOT range specific. The Head On or Off status remains the same as ranges are changed. Edits made to the head settings are independent of active range or RPT.

• The head height and fluid are shown on the graphical user interface display beside Head:on the Main Run Screen (see Section 4.1).

 OPERATION

See Section 4.7.6.3.

3.2.16 Purge

 PURPOSE

To execute the PPC4E test system Purge function using the optional Self Purging Liquid Trap (SPLT). Purge is used to collect and exhaust liquid contaminants from the device or system under test before they reach the PPC4E.

 PRINCIPLE

PPC4E is designed to precisely set, control and measure gas pressure. Liquid contamination of the PPC4E internal pressure control module and/or the RPT module(s) can cause poor pressure control and interfere with pressure measurement. Liquid contaminants that may be present in test devices or systems that are connected to the PPC4E TEST(+) port are likely to make their way back to PPC4E’s internal pneumatic system as the test device or system is pressurized and depressurized by PPC4E. To every extent possible, only clean hoses and tubing should be used to connect PPC4E to test devices or systems and those devices and systems should be free of liquid contaminants. However, in the event that PPC4E must used to test devices or systems that may contain small amounts of liquid contaminants, a Self Purging Liquid Trap (SPLT) accessory supported by the Purge function is available.

Execution of the PURGE function is automated and proceeds as follows:

If current pressure is greater than 700 kPa (100 psi) gauge, pressure is controlled down to less than 700 kPa (100 psi) gauge.

Pressure control stops and a 5 second wait occurs. SPLT exhaust valve is opened.

PPC4E waits until pressure is less than 20 kPa (3 psi) gauge or 110 kPa (16 psi) absolute. PPC4E internal vent valve is opened with the SPLT exhaust valve left open.

Note

• The Purge function makes use of the PPC4E valve driver option. Valve driver number 8 is used to actuate the SPLT exhaust valve. When making use of valve drivers, note that if the Purge function is enabled, valve driver number 8 will be actuated independently of valve driver commands. See Section 3.2.21.

• For the Purge function to execute an optional Self Purging Liquid Trap (SPLT) must be installed in the test line (see Section 2.3.6.1) and the function must have been enabled. Enable with: [Settings], <Internal>, Purge (see Section 4.7.12.3).

• at any time during execution of the purge routine causes the purge function to abort and returns to the Main Run Screen.

• The internal volume of the SPLT is about 20 cc. The SPLT will not operate effectively if the volume of liquid contaminants collected is greater than about 10 cc. The SPLT is designed to protect the PPC4E only against residual liquid contamination. Even if an SPLT is being used, precautions should be taken to reduce potential liquid contamination from the device or system under test as much as possible before making the connection to the PPC4E TEST(+) port.

• Do not plug the SPLT exhaust valve. The purge routine can not be completed with the SPLT exhaust valve plugged and the SPLT’s protective function will not be effective.

• If the SPLT is electrically connected to the PPC4E, its exhaust valve will always be open when the PPC4E vent valve is open. If desired, it may be closed manually using the Driver function (see Section 4.7.4).

 OPERATION

See Section 4.7.3.1.

3.2.17 Leak Test

 PURPOSE

To run an automated leak check routine that determines the leak rate of the system connected to the PPC4E TEST(+) port.

 PRINCIPLE

Leaks in the system connected to PPC4E’s TEST(+) port can cause differences between the pressure measured by the PPC4E RPTs and pressure in other parts of the test system. A large leak can cause the PPC4E to be unable to set and control pressures reliably. The LEAK CHECK function is provided as a means of checking and quantifying the leaks that may be present in the system.

The principle of the LEAK CHECK function is the measurement of the natural decrease or increase of pressure in a fixed volume over time. The LEAK CHECK function allows a leak check time to be set. The total pressure change and the average rate of change over the leak check time are calculated and displayed.

Note

• Changing the pressure in a test system causes adiabatic temperature changes in the gas that need to disipate before a valid leak measurement can be made. In general, a 30 second to 1 minute wait before running a leak check is adequate to allow the adiabatic temperature change to dissipate and valid leak measurements to be made. However, stabilization time may be much longer with larger volumes, higher pressures or with liquid test media.

• As a general rule, the maximum acceptable leak rate for optimal PPC4E automated pressure control operation and to ensure in tolerance measurements with default pressure control parameters is 0.5 % of current range span/minute.

• Leak check is range specific in the sense that leak check is run using the active range. However, only one set of leak check results is maintained in memory and each leak test completed overwrites the memory. View leak check always shows the results of the last leak check run regardless of the range that is now active. The results screen includes the range indicator to indicate the range in which the leak check was run.

 OPERATION

See Section 4.7.3.2.

3.2.18 Resolution

 PURPOSE

To set the resolution with which measured pressures and other pressure indications and settings are displayed.

 PRINCIPLE

The resolution with which PPC4E displays pressure values can be adjusted. This feature can be used to reduce the resolution when lower precision measurements are being made and excess resolution might confuse or distract the operator.

The resolution setting determines the number of digits with which pressure is displayed. The resolution is calculated based on the full scale of the range and then rounded to the furthest digit to the right. For example, resolution of 0.001 % on a range of 150 kPa is 150 X 0.001 % = 0.0015 which is rounded down to 0.001 kPa.

Note

• Default resolution is 10 ppm of active range span. Resolution is set automatically by AutoRange (see Section 3.2.7).

• The resolution setting is range specific. A resolution setting made in one range does NOT affect other ranges.

• The measured pressure resolution is fixed for altitude units at 1 m in meters and 1 ft in feet.

• The maximum resolution setting is limited in AutoRange ranges that are less than 10% of the active RPT default full scale.

 OPERATION

See Section 4.7.6.4.

3.2.19 Jog

 PURPOSE

Adjust the nominal change in pressure caused by using the jog direct pressure control keys ( and ) or the front panel knob when available.

 PRINCIPLE

The jog direct pressure control keys,  and , increase or decrease pressure by a nominal amount each time they are pressed. If pressure control is NOT active, pressing the jog key causes an up or down slow pressure ramp. If pressure control is active, the jog key causes the pressure control target value to be changed by the amount of the jog step.

“Knob jog” is available by menu selection when dynamic control is active or during Auto Test (see Sections 3.2.2.1 and 3.2.14). knob jog opens a screen in which rotating the knob one “click” to the right increases the control target by the jog step and rotating the knob one “click” to the left decreases the control target by the jog step.

Note

• The default jog step is 100 ppm of active range span. The maximum jog step is 5% of active range span. Jog step value is set automatically by AutoRange (See Section 3.2.7).

• The jog step setting is range specific. A jog step setting made in one range does NOT affect other ranges.

 OPERATION

In document PPC4E Pressure Controller/Calibrator (Page 31-119)