This chapter tells how to configure the analog and discrete inputs and outputs and serial communication ports.
Hardware Options
The Antisurge Controller uses either the Basic Compressor Control-ler (BCC) or Extended Compressor ControlControl-ler (ECC) hardware configuration, as described in the Components and Configurations section in Chapter 1 of IM300/H. Either provides the following input and output circuits:
• eight Analog Inputs (CH1 to CH8),
• two standard Analog Outputs (OUT1 and OUT2),
• seven Discrete Inputs (D1 to D7),
• five Discrete Outputs (CR1 to CR5), and
• four Serial Ports (Port 1 to Port 4).
When the ECC configuration is used, all I/O terminals are provided on a separately mounted Field Input/Output Module (FIOM), which is connected to an Extended I/O Back Panel by a High-Density Interconnect Cable (HDIC).
Disabling Input Signals
As an aid to developing and demonstrating Series 3 Plus Antisurge Controllers, they include a CPU Inputs Lockout [MODE:D LOCK 6]
parameter that, when enabled, configures the controller to ignore its analog and discrete inputs (which can then be updated via the Port 3 or Port 4 Modbus serial link).
Note:
The availability of the discontinued FIOM cannot be guaranteed.Caution:
An installed controller should not be operated with LOCK 6 enabled, as that would prevent it from receiving needed input signals.38 Chapter 3: Input/Output Features
Figure 3-1 Analog input signal processing
Analog Inputs
Each Series 3 Plus Controller is equipped with eight analog inputs.As described in the Analog Input Installation section in Chapter 6 of IM300/H, they are set up as either 0 to 5 Vdc or 4 to 20 mA inputs by installing resistors on either the Field Input/Output Module or setting jumpers on the Analog PCB Assembly (if not using FIOMs).
In this manual, we will refer to both the input circuits and their analog signals as Channels 1 through 8 (CH1 to CH8) — the meaning in each case should be clear from its context.
The processing of these inputs and the terms used to distinguish their intermediate values are illustrated by Figure 3-1:
Step 1: The raw analog inputs are converted to equivalent digital values called Analog-to-Digital Variables (AD1 to AD8).
Step 2: Transmitter Testing compares each AD variable against its individual alarm limits.
Step 3: The AD variables are converted into percent-of-range Signal Variables (SV1 to SV8).
Step 4: Gains and biases are then applied to obtain the Process Variables (PV1 to PV8) used by the control calculations.
Step 5: The signal variables are also independently scaled to obtain the Measured Variables (MV1 to MV8) displayed by the AUXil-iary readout’s Analog In Menu.
AD (%)
Analog-to-Digital Variables
The input circuitry converts the analog input signals into equivalent digital values for use by the CPU. Each signal is passed through a hardware filter to remove unwanted high frequency components, and a windowing filter that samples each signal several times per scan cycle and reports the resulting average.
Because these values are generated by an analog-to-digital con-verter, we refer to them as analog-to-digital variables (AD1 to AD8).
They are reported to the CPU as percentages of the analog signal’s full-scale value. For example, a 20 mA signal would be reported as 100 percent, while 4 mA would be reported as 20 percent.
Transmitter Testing
The controller tests each analog input against a user-defined range.
If any of them is outside of its range, the front-panel TranFail LED is lit, any Transmitter Failure (Tran) relays are energized and the Mod-bus Tran Fail discrete is set. You can use the Transmitter Status Test [MODE:D ANIN –] to identify the failed input.
This feature is configured by defining the Analog Input Low Alarm Limit [MODE:D ANIN # LOW] and Analog Input High Alarm Limit [MODE:D ANIN # HIGH] for each input, which are set as percent-ages of the full-scale analog-to-digital variables. For example, you would enter AN IN LOW as 15.0 percent to set the lower limit of a 4 to 20 mA signal to 3.0 mA.
Because an analog input can never be higher than 102.4 (A2.4) nor lower than 00.0, setting ANIN HIGH and LOW to these values has the effect of excluding that channel from the transmitter alarm fea-ture. Using these values for unused inputs prevents them from interfering with the proper operation of this feature.
Signal Variables
Each analog-to-digital variable is then converted to a percent-of-range signal variable according to whether or not the corresponding transmitter uses an offset zero (for example, 4 to 20 mA or 1 to 5 Vdc). Signals that are so offset are scaled as:Otherwise, the signal variable is set equal to the analog-to-digital variable (AD). In either case, the SV values are constrained to the range 00.0 to 100.0 percent. Higher values are changed to 100.0, lower values to 00.0. You can use the Signal Values Test [MODE TEST 4] to directly examine these signal variables from the Engi-neering Panel.
Any signal that has an offset zero (for example, a 4 to 20 mA input) must be identified by enabling the corresponding Offset Zero Input [MODE:D ANIN #]. Signals that are not offset are identified by dis-abling the corresponding parameter.
SV = 1.25⋅(AD–20 percent)
40 Chapter 3: Input/Output Features
Process Variables
The analog inputs for some control calculations must be converted to absolute values. For example, the pressure measurements used to compute a compression ratio must be scaled as percentages of the highest absolute pressure either of their sensors can measure.To this end, the controller converts its signal variables into process variables by applying appropriate gains and biases:
where:
Bias = (Offset · 100) / Maximum Gain = Range / Maximum
Maximum = absolute measurement corresponding to the highest possible transmitter signal. If there is more than one transmitter of a given type, this should be the largest such value for the group
Offset = absolute measurement corresponding to lowest possi-ble transmitter signal
PV = Process Variable, expressed as a percentage of abso-lute maximum
Range = span of the transmitter in question
The gain and bias for each process variable must be assigned to the corresponding Process Variable Gain [COND:D GAIN #] and Pro-cess Variable Bias [COND:D BIAS #]. For unused channels, set the gain to 1.000 (.A00) and the bias to 00.0.
Measured Variables
The AUXiliary Display’s Analog In menu is used to display the con-troller’s eight signal variables, scaled to appropriate ranges, along with descriptive labels of your choosing. For example, you might dis-play an inlet temperature signal as:
The available choices are set up by each input’s five Measured Vari-able [COND:D DISPLAY 0] parameters. For example, the DISPLAY 0 1 parameters govern the display of signal variable SV1:
• Each Measured Variable Display [COND:D DISPLAY 0 #]
parameter defines whether the corresponding variable can be viewed (SV1 can be displayed only if DISPLAY 0 1 is On).
• Each Measured Variable Label [COND:D DISPLAY 0 # –]
parameter defines the label that will precede the numeric value of the input. Each can be any combination of eight symbols from Table 3-1. The default labels [see page 5 of DS301/O], can be restored by entering the COND:D DISPLAY 0 0 key sequence.
PV = Gain SV⋅ +Bias
TempIn: 400
• Each signal variable’s Measured Variable Minimum [COND:D DISPLAY 0 # LOW] defines the digits shown when it is zero, its Measured Variable Maximum [COND:D DISPLAY 0 # HIGH]
defines the digits shown when it is 100 percent, and its Mea-sured Variable Decimal [COND:D DISPLAY 0 # •] defines the decimal point position. Mathematically, this can be stated as:
where nSV is the signal variable’s normalized value.
Because the decimal point is a character that requires one of the four display positions, only three digits can be displayed unless that parameter is disabled (Off). In other words, that parameter identifies the digit the decimal should replace (that and all less-significant dig-its are shifted one position to the right). A value of one corresponds to the right-most, least-significant digit, while four is the left-most, most-significant digit. Thus, if DISPLAY 0 1 HIGH is 3210, the five possible values of DISPLAY 0 1 • would yield the following displays when SV1 is 100 percent:
0: 3210 1: 321. 2: 32.1 3: 3.21 4: .321 To obtain the most precise possible readouts, you should always make the DISPLAY HIGH parameters as large as possible. For example, if you want to display three digit numbers from 0 to 600, set DISPLAY HIGH to 6000 and DISPLAY • to 1 (for a trailing deci-mal). This will give more precise readouts than you would get by setting DISPLAY HIGH to 0600 and DISPLAY • to 0.
If Auxiliary Display Reset [MODE:D LOCK 9] is disabled, Measured Variables will be displayed until another variable is selected. Other-wise, the operating state display is restored 60 seconds after the MENU or SCROLL key was last pressed.
Table 3-1 Available symbols for measured variable labels
MV = [Min+(nSV)⋅(Max–Min)]⁄10dec
Î Í Ì ± ¥ Ò
space! " # $
% & ' ( ) * + , - . /
0 1 2 3 4 5 6 7 8 9 : ; < = > ? @
A B C D E F G H I J K L M N O P
Q R S T U V W X Y Z [ \ ] ^ _ `
a b c d e f g h i j k l m n o p
q r s t u v w x y z
42 Chapter 3: Input/Output Features
Analog Outputs
The Antisurge Controller has two standard analog outputs, both of which are generated as both 4 to 20 mA and 0 to 5 Vdc signals (although only one of these signals can be used for each output):• Unless the control response is sent to a companion valve-shar-ing controller (see Valve Sharvalve-shar-ing on page 91), OUT1 is used to manipulate the compressor’s recycle or blowoff valve (see Actu-ator Control Signal on page 99).
• OUT 2 is generated as the equivalent of one of the variables listed in Table 3-2, as specified by the Second Output Assigned Variable [COND:D OUT 2]. It can be used to drive a readout or graphical display or be connected to a DCS analog input.
The Output Loopback Test can be used to compare the actual out-put signal to its intended value, while the Valve Position Test can be used to compare the measured and intended positions of the final control element.
Table 3-2 Functions for OUT2
Output Loopback Test
The controller can be configured to energize one or more discrete outputs to indicate an excessive deviation between the measured and intended values of the actuator control signal.
This feature is set up by connecting OUT1 to analog input CH8, as described in the Analog Output Installation section in Chapter 6 of IM300/H. Any discrete output assigned the output failure (OutF) function would then energize if SV8 differed from the intended actu-ator control signal by more than five percent, or if the value of CH8 was outside of its Transmitter Testing range.
Code Signal
Out Actuator Control Signal (see page 99) Flow Displayed Flow (see page 61)
S proximity to Surge Control Line (see page 72) UsrQ Displayed Net Flow (see page 62)
Valve Position Test
The controller can also be configured to energize one or more dis-crete outputs to indicate an excessive deviation of the measured and intended positions of the final control element.
This feature is set up by connecting a valve position signal to analog input CH7:
• For a signal-to-open control element, the position signal must increase as the control element opens.
• For a signal-to-close control element, the position signal must decrease as the control element opens.
Any discrete output assigned the position failure (PosF) function would then energize if SV7 differed from the intended actuator con-trol signal by more than the Position Failure Threshold [COND:D LVL 5] for at least the Position Failure Delay [COND:D CONST 5], or if the value of CH7 was outside of its Transmitter Testing range.
44 Chapter 3: Input/Output Features
Discrete Inputs
All Series 3 Plus Antisurge Controllers are equipped with seven discrete inputs (D1 to D7) that can be used to trigger the control fea-tures listed in Table 3-3. The threshold level above or below which these inputs are asserted or cleared is listed on the Series 3 Plus Compressor Controllers Hardware Specifications [DS300/H]:ESD Setting D2 will trigger an emergency shutdown, provided that fea-ture is enabled (see Operating State Request Signals on page 103).
Output Tracking Setting D4 will cause the actuator control signal to track a specified analog input, provided that feature is enabled (see Output Tracking on page 102).
Purge Setting D3 will fully close the recycle valve, provided that feature is enabled and the controller is operating in its Stop state (see Operat-ing State Request Signals on page 103).
Recall Setting D7 will recall the second alternate parameter set and clear-ing it will recall the first, provided that feature is enabled (see Alternate Parameter Sets on page 106).
Reset SO Setting D5 will reset the Cumulative Surge Count to zero (see Surge Counters on page 76).
Stop Setting D6 will select the Stop state and clearing it will select the Run state, provided that feature is enabled (see Operating State Request Signals on page 103).
Tracking Setting D1 will cause this controller to track the operation of a com-panion Antisurge Controller, provided that feature is enabled (see Redundant Control on page 36).
The states of these inputs can be displayed on the front-panel AUX readout by pressing the SCROLL key while the operating STATUS is displayed. “DGI= 1234567” is then displayed, where each digit appears only if that discrete input is set.
Table 3-3 Discrete input functions Input Function
D1 Redundant Tracking request
D2 Emergency Shutdown (ESD) request D3 Purge request
D4 Output Tracking request D5 Reset SO (Safety On) request D6 Normal Shutdown (Stop) request D7 Recall alternate parameter set
Discrete Outputs
The controller’s discrete outputs can be used to automatically trigger alternate control measures or to control External Alarms for a variety of process and controller conditions.
The operation of each relay is set by selecting one of the conditions from Table 3-4 as its Relay Assigned Function [MODE:D RA #].
Except for the Fault Relays, each can either energize or de-energize when that condition is detected:
• If its RA parameter has a positive value, the assigned condition energizes it.
• If that parameter is negative, that condition de-energizes it.
For example, if MODE:D RA 3 is assigned the value +Tran and is normally open, CR3 will be energized and its associated circuit will be closed whenever any analog input is outside the range of its transmitter testing limits. If it is given the value –Tran, that condition would cause CR3 to de-energize.
Whether energizing a relay opens or closes its circuit depends on the position of its NO/NC jumper, as described in the Discrete Out-put Jumpers section in Chapter 5 of IM300/H.
The states of these outputs can be displayed on the front-panel AUX readout by pressing the SCROLL key twice while the operating STATUS is displayed. “DGO= 12345” is then displayed, where each digit appears only if that discrete output is energized.
Fault Relays
Discrete output CR1 is hard-wired as a fault relay, but can also be given one additional function. CR2 can be set to de-energize when-ever CR1 does by setting a jumper on that assembly (its assigned function then affects only its Modbus DO State discrete bit).The operation of the controller’s fault relays and LED are described in the Fault Indicators section in Chapter 8 of IM300/H.
External Alarms
You can use the controller’s discrete outputs to control external indi-cators (lights, horns, etc.) for any of the conditions described below.However, setting up and interpreting such alarms can be confusing because three different factors affect whether they indicate that the assigned condition does or does not exist:
• If the assigned function is positive, any non-fault relay energizes when that condition occurs. Relays with negative functions will de-energize when those conditions occur.
• The relay circuits in the controller can be set for normally-open operation (energizing the relay completes the circuit) or nor-mally-closed operation (energizing the relay opens the circuit).
• The alarm device itself may light or sound when its control cir-cuit is completed, or when it is opened.
46 Chapter 3: Input/Output Features
Table 3-4 Discrete output functions
Unless otherwise noted, the following descriptions assume each alarm circuit is set up to indicate that its assigned condition exists:
Always Set Relays assigned the +On function de-energize only if the controller loses power, those with the -On function are always de-energized.
Fault Relays given the -On function never energize.
Automatic The Auto function indicates the controller is operating automatically.
Manual Override The MOR function indicates the antisurge control response is being manually controlled with no automatic surge protection (see Manual Override on page 33).
Never Set Relays assigned the +Off function are always de-energized, those with the -Off function de-energize only if the controller loses power.
Fault Relays are often given the -Off function.
Output Failure The OutF function indicates a failure of analog output OUT1 (see Output Loopback Test on page 42).
Position Failure The PosF function indicates an excessive deviation of the measured valve position from its intended value (see Valve Position Test on page 43).
Pressure Limit The Lim function indicates a pressure limiting control response is greater than zero (see Pressure Limiting on page 82).
Code Function
Auto Automatic operation Lim Pressure Limiting
MOR Manual Override (no automatic protection) Off Never Set
On Always Set
Open control Valve Open OutF analog Output Failure PosF valve Position Failure RT Recycle Trip condition Run Run State
SerC Serial Communication Error SO Safety On condition
Surg Surge Event Tran Transmitter Failure
Recycle Trip Relays assigned the RT function are asserted when the operating point moves to the left of the Recycle Trip Line (RTL). If the control-ler is operating manually, such indicators are not cleared until the Recycle Trip Response restores an adequate safety margin. If it is being manually operated, they are cleared as soon as the operating point moves back to the right of the RTL (see Recycle Trip Line on page 73 and Recycle Trip Response on page 80).
Run State The Run function indicates the controller is modulating the recycle valve to prevent surge (see Operating State on page 103).
Safety On Relays assigned the SO function are asserted when the controller detects a presumed surge and invokes the Safety On Response.
Such indicators are not cleared until the surge count is zeroed (see Safety On Response on page 75).
Serial Communication Error
The SerC function indicates the controller has failed to detect an expected transmission on its Port 1 or 2 communication network (see Serial Communication Errors on page 49).
Surge Event If the Surge Event Duration is not zero, relays assigned the Surg function are set when the event surge count reaches the Surge Event Threshold and remain set only until the event timer expires (see Surge Counters on page 76). Thus, such relays should be used to trip an edge-triggered response (such as an emergency shut-down) or device (such as a latched alarm).
If the Surge Event Duration is set to zero, relays given this function are set when the cumulative surge count reaches the Surge Event Threshold and remain set until that count is zeroed.
Transmitter Failure The Tran function indicates at least one analog input signal is not within its valid range (see Transmitter Testing on page 39).
Valve Open The Open function is asserted when the actuator control signal is greater than the low output clamp, thus indicating the control valve is open (see Output Clamps on page 100). It is particularly useful when that clamp is not zero, in which case it can be difficult to tell if the valve is open just by looking at the OUT readout.
48 Chapter 3: Input/Output Features
Figure 3-2 Communication with other controllers
Serial Ports
Series 3 Plus Controllers are equipped with four serial ports for com-municating not only with other Series 3 Plus Controllers, but also with host computers and supervisory control systems:• Port 1 is used for circulating information among the Series 3 Plus controllers regulating a single rotating equipment train.
Antisurge Controllers use it primarily for coordinating control with companion Antisurge and Performance Controllers. A max-imum of eight controllers may be connected to any one Port 1 network.
• Port 2 is used for communicating load-sharing and performance override control information.
• Port 3 is used for computer communication and control, using the Modicon Modbus RTU protocol.
• Port 3 is used for computer communication and control, using the Modicon Modbus RTU protocol.