FC 80 - Control Station

There are three types of stations, each controllable through a digital (NDCS03) or analog (IISAC01) control station and/or a human system interface (HSI). The types include basic, cascade and ratio stations.

 

A basic station generates a set point (SP) and provides manual/automatic transfers, control output adjustments in manual control mode, and set point adjustments in automatic control mode.

 

A cascade station provides the same functions as a basic station plus an additional mode that allows the set point to be controlled by external input signal <S2>.

 

A ratio station provides the same functions as a basic station, but differs from the cascade station in its method of set point generation while in the ratio mode. The wild variable <S2> multiplied by a ratio adjustment factor (ratio index) determines the set point output while in ratio mode. The initial ratio index value is calculated by the station to maintain the current set

point output value when the station is placed into the ratio mode. While in the ratio mode, the ratio index value is displayed in place of the set point value and can be adjusted (ramped up or down) by the operator to obtain the desired set point output.

 

Station control allows changing the mode, set point, ratio index and control output of a control station by manipulating a control station element.

 

The control output (CO) value during startup is configurable. If S16 defines a DCS station (S16 equals zero through seven) or SAC station (S16 equals zero through 63), then the control output during startup tracks the displayed control output on the DCS station or SAC station. If a communication failure exists for the station (or S16 equals 255), then the control output tracks the CO track signal <S4> during startup.

 

NOTE: Valid station addresses are zero through 63 and 100 through 163 for Harmony controllers at 40 kilobaud.

 

The associated analog output (AO) <S28> generates auto-bypass when the AO has bad quality and communicates this state to the control interface module analog output.

 

NOTES:

  1. The maximum ratio for the wild variable is ten when using a DCS station and 100 when using a SAC station. The minimum practical ratio is 0.05.

  2. The local SAC/DCS link communication baud rate is set by the hundreds digit S3 of the extended executive block (function code 90, block 20) for Harmony controllers. The remote SAC link located on CIO-100 Harmony I/O blocks is not affected by the S3 specification setting.

 

 

 

 

Outputs:

 

Blk

Type

Description

N

R

Control output (0% to 100%)

N+1

R

Set point

N+2

B

Automatic mode flag:

0 = manual

1 = automatic

N+3

B

Level flag:

0 = local

1 = computer

N+4

B

Cascade/ratio mode flag:

0 = basic

1 = cascade/ratio

N+5

B

Computer status flag:

0 = computer OK

1 = computer failed

 

 

 

Specifications:

Spec

Tune

Default

Type

Range

Description

S1

N

5

I

Note 1

Block address of input to be displayed on the PV

scale of a station (can be used for SP track S30)

S2

N

5

I

Note 1

Block address of SP track signal (S29 SP track

switch)

S3

N

5

I

Note 1

Block address of auto signal

S4

N

5

I

Note 1

Block address of control output track signal (TR)

S5

N

0

I

Note 1

Block address of control output track switch (TS):

0 = no track

1 = track

S6

N

5

I

1, 2, 3, 5, 6, 7 or 8

Initial mode of station after startup:

1 = computer, manual

2 = computer, auto

3 = computer, cascade/ratio

5 = local, manual

6 = local, auto

7 = local, cascade/ratio

8 = previous mode

S7

Y2

9.2E18

R

Full

PV high alarm point in engineering units

S8

Y2

-9.2E18

R

Full

PV low alarm point in engineering units

S9

Y2

9.2E18

R

Full

PV-SP deviation alarm point in engineering units

(for console only)

S10

N

100.000

R

Full

Signal span of PV in engineering units

S11

N

0.000

R

Full

Zero value of PV in engineering units

S12

N

0

I

Full

PV engineering units identifier (for console only)

S13

N

-5.000

R

Full

Signal span of SP in engineering units

S14

N

0.000

R

Full

Zero value of SP in engineering units

S15

N

0

I

Full

SP engineering units identifier (for OIS console only)

S16

N

255

I

Full

Control station address:

254 = passive station

255 = no station

S17

N

0

I

0 - 7

Mode of system default if the computer fails while

the loop is under computer control:

0 = computer (auto/manual mode unchanged)

1 = computer, manual

2 = computer, auto

3 = computer, cascade/ratio

4 = local (auto/manual mode unchanged)

5 = local, manual

6 = local, auto

7 = local, cascade/ratio

S18

N

0

I

Note 1

Block address of the transfer to manual signal:

0 = no transfer

1 = transfer to manual and hold

S19

N

0

I

Note 1

Block address of the transfer to auto signal:

0 = no transfer

1 = transfer to auto and hold

S20

N

0

I

Note 1

Block address of the transfer to cascade/ratio signal:

0 = no transfer

1 = transfer to cascade/ratio and hold

S21

N

0

I

Note 1

Block address of the transfer to local signal:

0 = no transfer

1 = transfer to local and hold

S22

N

0

I

Note 1

Block address of the transfer to computer signal:

0 = no transfer

1 = transfer to computer and hold

S23

N

0

I

0 - 4

Station type:

0 = basic with set point

1 = basic without set point

2 = basic with bias

3 = ratio

4 = cascade

S24

N

0

I

Note 1

Block address of external high absolute alarm flag:

0 = no alarm

1 = high absolute alarm

S25

N

0

I

Note 1

Block address of external low absolute alarm flag:

0 = no alarm

1 = low absolute alarm

S26

N

0

I

Note 1

Block address of external high deviation alarm flag:

0 = no alarm

1 = high deviation alarm

S27

N

0

I

Note 1

Block address of external low deviation alarm flag:

0 = no alarm

1 = low deviation alarm

S28

N

2

I

Note 1

Block address of analog output associated with this

station

S29

N

0

I

Note 1

Block address of switch to have SP track <S2>:

0 = no track

1 = track <S2>

S30

N

0

I

Note 1

Block address of switch to have SP track <S1> (PV):

0 = no track

1 = track <S1>

S31

N

60.000

R

Full

Computer watchdog time period (in secs)

 

 

80.1 Explanation

 

80.1.1 Outputs

 

N

Control output expressed in percent. The station mode and the control output auto <S3> input determine the control output.

 

N+1

Set point expressed in engineering units. The input to <S2> and the station mode determine the set point output.

 

N+2

Mode indicator.

0 = manual

1 = automatic

 

N+3

Level indicator.

0 = local

1 = computer

 

N+4

Station mode indicator.

0 = basic

1 = cascade/ratio

 

N+5

Computer status flag.

0 = computer OK

1 = computer failed, station mode dependent on S17

 

 

 

80.1.2 Specifications

 

S1 - PV

Block address of the input to be displayed on the PV scale of a station (can be used for SP track S30). This input drives the control station process variable indicator (in engineering units).

 

S2 - SPT

Set point track signal. For stations in basic mode, S2 is an external set point track signal. For stations in the cascade mode, <S2> is the cascade input. For stations in ratio mode, <S2> is the uncontrolled or wild variable. Table 80-1 shows the trackbehavior of the station block.

 

NOTE: For stations in ratio mode, the wild variable must be limited to positive numbers, and the set point range must be a positive number. Low limits on either signal must not be less than zero.

 

Table 80-3 Track Behavior of the Station Block

Station Mode

Manual

Auto

Cascade

Ratio

Basic

A

A

--------

-------

Cascade

A

A

B

-------

Ratio

A

A

--------

C

 

 

NOTE:

A = When the station tracks and what it tracks depends on <S29> and <S30>. Specification S29 indicates when <S2> should be tracked, and <S30> indicates when <S1> should be tracked. If both indicate tracking, <S29> takes precedence.

B = Specification S2 is tracked unconditionally and the station displays <S2>.

C = Specification S2 multiplied by the ratio index (displayed in digital set point display), is tracked unconditionally and the product of <S2> and the ratio index displays on the station Bar graph.

 

S3 - CO AUTO

Block number whose output value is the control output when the station is in automatic mode (usually the output of a PID block).

 

S4 - CO TRACK

Block number whose output is the control output when the station is tracking (<S5> equals one). Specification S4 also provides a reference for the station control output when the  module completes its startup mode, if an active hard station is not present.

 

S5 - CO SWITCH

Block number whose output value determines whether the control output is to track <S4>.

0 = no tracking

1 = track

 

NOTE: Both the MAN and AUTO lights on the digital control station (NDCS01) light when the module is in the control output override mode (tracking). For the NDCS03 station, just the track light is displayed. The manual/auto status flag does not change when in override state. The actual operating state is saved and will be restored when the track flag goes to zero (normal). This note is not applicable to the analog control station (IISAC01).

 

S6 - SMODE

Initial mode of the station after startup. For the configurable startup period after power up/reset/switch to execute mode, the station will be in local manual mode. After the startup period expires, the mode is as indicated by S6 unless overridden by <S18> to <S22>. Specifications <S18> through <S22> change the station mode and control level through logic. Any of

these specifications override S6. When adding a station block with S6 set to previous mode (eight), the actual mode will be local manual until modified by the operator or logic. When selecting computer or local cascade ratio, cascade or ratio control will be implemented depending on S23 (station type).

1 = computer manual

2 = computer auto

3 = computer cascade/ratio

5 = local manual

6 = local auto

7 = local cascade/ratio

8 = previous mode

 

S7 - PVH

Sets the engineering units value of the process variable that a high alarm generates and displays on the Human System Interface (HSI).

 

S8 - PVL

Sets the engineering units value of the process variable that a low alarm generates and displays on the control station or HSI.

 

S9 - PVDEV

Engineering units value of allowed deviation between the process variable and set point. A high deviation alarm generates when the process variable is greater than the set point and the value of the difference between the two is greater than or equal to S9. A low deviation alarm generates when the process variable is less than the set point and the value of the difference between the two is greater than or equal to S9. These alarm conditions report to the HSI.

 

S10 - PVSPAN

Sets the signal span of the process variable in engineering units.

 

S11 - PVZERO

Zero value of the process variable in engineering units.

 

S12 - PVEU

Process variable engineering units identifier, used by the HSI.

 

S13 - SPSPAN

Sets the signal span of set point in engineering units. When left at default, set point span equals span defined by S10. The default setting for S13 is -5.000. It should be noted that HSIs will display the PV span (S10) for the set point span (S13). The Harmony controllers use the PVSPAN (S10) and PVEU (S12) for both the process variable and set point as long as the set point span is set to the default value.

 

NOTE: Some DCS stations will not function correctly using the -5.000 default value. If a problem exists, set S13 and S14 the same as S10 and S11.

 

S14 - SPZERO

Zero value of set point in engineering units.

 

S15 - SPEU

Set point engineering units identifier, used by the HSI.

 

S16 - DCSADR

Set S16 to the control station address (254 equals passive station and 255 equals no station). Valid station addresses are zero through seven and 100 through 107 for DCS stations, and zero through 63 and 100 through 163 for SAC stations. Addresses 100 through 163 represent actual station addresses of zero to 63. If selecting addresses 100 through 163, the

Harmony controllers will not report the status of the control station in the module status or module problem reports. In all other respects, station operation remains unchanged. This specification must be set to 254 when a passive station interface (function code 139) S1 points to this function code.

 

NOTE: Valid station addresses are zero through 63 and 100 through 163 for the Harmony I/O CIO-100 and for Harmony controllers at 40 kilobaud.

 

S17 - CFAIL

Defines the mode the station will default to in the event of a computer failure while it is under computer control. When selecting computer or local cascade/ratio, the station assumes cascade or ratio control depending on S23.

 

0 = computer manual/auto mode unchanged

1 = computer manual

2 = computer auto

3 = computer cascade/ratio

4 = local manual/auto mode unchanged

5 = local manual

6 = local auto

7 = local cascade/ratio

 

S18 through S22

Block addresses that change the station mode and control level through logic. If more than one (<S18> through <S22>) are set, <S18> takes precedence over <S19>, which takes precedence over <S20>, etc. If the station is in manual mode, <S20> places the station in automatic and cascade/ratio mode simultaneously. When both <S21> and <S22> are set,

<S21> overrides <S22>.

 

NOTE: When one or more inputs to <S18> through <S22> equal one, the station displays the interlock state. The station is locked in a particular mode. The output cannot be changed by the operator unless S18 equals one. Inputs <S18> through <S22> are typically driven by fault logic that places the control loop in a known condition when a failure is detected. Removing an interlock state leaves the current mode unchanged, but allows the operator to change the mode.

 

S18 - MANXFR

Block address of the transfer to manual signal.

0 = no transfer

1 = transfer to manual

 

S19 - AUTOXFR

Block address of the transfer to auto signal.

0 = no transfer

1 = transfer to auto

 

S20 - CSRXFR

Block address of the transfer to cascade/ratio signal. This specification transfers to cascade or ratio control depending on

the type of station selected with S23.

0 = no transfer

1 = transfer to cascade/ratio

 

S21 - LOCLXFR

Block address of the transfer to local signal.

0 = no transfer

1 = transfer to local

 

S22 - CMPXFR

Block address of the transfer to computer signal.

0 = no transfer

1 = transfer to computer

 

S23 - STNTYP

Provides a choice between several station types for normal operation. The definition of <S2> depends on S23. The value of

S23 also determines whether cascade or ratio control is adopted when S6, S17 and <S20> are set to cascade/ratio (refer to

S6). This specification will not be fully operational until the HSI display strategies are modified. Until that time, only zero,

three and four are valid type specifications.

0 = basic with set point

1 = basic without set point (presently not implemented)

2 = basic with bias (presently not implemented)

3 = ratio

4 = cascade

 

S24 through S27

Block addresses that provide a mechanism for external absolute and deviation alarming. Specifications S24 and S25 can

be used for end of travel alarms. Specifications S24 through S27 are logical ORed with their respective internal alarms,

defined by S7 through S9, to determine the alarm states presented to the operator.

 

S24 - EHALRM

Sets the external high absolute alarm flag.

0 = no alarm

1 = high absolute alarm

 

S25 - ELALRM

Sets the external low absolute alarm flag.

0 = no alarm

1 = low absolute alarm

 

S26 - EHDALRM

Sets the external high deviation alarm flag.

0 = no alarm

1 = high deviation alarm

 

S27 - ELDALRM

Sets the external low deviation alarm flag.

0 = no alarm

1 = low deviation alarm

 

S28 - AOBLK

Analog output block number associated with the station. Use this specification for proper operation of bypass logic. When S28 equals zero or two, it is not used. Any setting other than zero or two must be a block number of the control interface module (CIS) function code 79, the analog output/slave (ASO) function code 149, the analog output/channel (AO/CH) function code 223, or the device definition (DD) function code 221.

 

NOTES:

  1. Only the physical AO from function code 79 is referenced to check the quality of the AO for auto bypass when the quality is bad. When using function code 79, S28 should reference output block N+4 or N+5, not output block N.

  2. When specification S28 is connected to block output number four of a device definition (function code 221) function block, the bypass logic of the control station (function code 80) function block operates in the same manner as when specification S28 is set to zero or two. The operational difference between referencing the device definition function block and setting specification S28 to zero or two is that when specification S28 references the device definition function block, the control station function block interfaces to a SAC station attached to a control I/O (CIO) block.

  3. When specification S28 is connected to the block output of an analog output/channel (function code 223) function block and specification S16 specifies a valid SAC address, the control station function block interfaces to a SAC station attached to a control I/O block.

  4. When an analog out/channel (function code 223) function block is placed into simulation (specification S15 of function code 223 set to 1) its associated control station function block will place its SAC station (auto-bypass enabled) into bypass operation with its demand output set to the last non-simulated control output value and function code 223 will not set the suspect bit. The auto-bypass SAC station will remain in bypass operation until the simulation option is disabled and the current control output value is set to match the control output value that was in effect prior to the simulation.

  5. The IISAC01 analog control station bypass function takes a higher precedence in the control of the analog output field element it shares in common with the CIO 100 block. This means that the bypass functionality takes precedence over function code 223 undefined, override, simulation, and normal modes of operation. It also takes precedence over function code 79 undefined and normal modes of operation.

  6. Specification S28 may be connected to an analog output channel (function code 223) that is associated with an AOT analog output channel. In this application an IISAC01 is not used and S16 is set to 254 or 255. The station (function code 80) function block will transfer to manual only if both redundant AOT Harmony I/O blocks experience failures on that particular channel.

 

Specification S28 provides a way to automatically monitor the CIO block/CIS module or AOT block/ASO module output channel. Should the CIO block/CIS module or AOT block/ASO module detect a fault on the current output, the station transfers to manual. If using a control station with a CIO block/CIS module, selecting auto-bypass on the station causes it to transfer to bypass when the output faults.

 

NOTE: The HSI does not indicate that the station is in bypass or locked in manual (as it does if S18 equals one).

 

 

 

S29 - SPTRCK

Block address of the analog output set point track signal. This determines the track behavior of the set point in conjunction with <S30>. Specification S29 indicates when <S2> should be tracked, and <S30> indicates when <S1> should be tracked. If both indicate tracking, <S29> overrides <S30>. If this specification equals one, it will cause the set point to track <S2> whether the station is in manual or automatic mode. This specification is not applicable when the station is in cascade mode because the cascade input uses none of the internal station logic for control.

0 = no track

1 = track <S2>

 

S30 - PVTRCK

Block address of the process variable track signal. It determines the track behavior of the set point in conjunction with <S29>. Specification <S29> indicates <S2> should be tracked, and <S30> indicates <S1> should be tracked. If both indicate tracking, <S29> overrides <S30>. When <S30> equals one, it causes the set point to track <S1> whether the station is in automatic or manual mode. This specification is not applicable when the station is in cascade mode because the cascade input uses none of the internal station logic for set point control.

0 = no track

1 = track <S1>

 

S31 - CMPWDG

Computer watchdog time-out interval times computer communications when a station is under computer control. Timing starts when a computer OK message goes from the network interface to the module, signifying that the computer received all information transmitted from the module. The timer is reset by each subsequent OK message from the network interface and station variable settings.

 

For example, if the station is switched from manual to computer control, a message will be sent to the network interface, which will generate an OK message and initiate timing. If the elapsed time between OK messages exceeds the value of S31, the timer times out. The control mode is then determined by the value of S17 (computer watchdog time-out option) in

the station. If the computer replies to a module message before the time interval is over, the timer resets itself and begins timing again with the next communication. The interval is selected in seconds, with a default value of 60 seconds. An interval value of 0.0 disables the computer watchdog time-out feature.

 

80.2 Applications

 

Figure 80-1 illustrates a single input, single output control loop run by a control station in basic mode (function code 79). This configuration uses a PID block for error correction. The process variable and the control output interface with the field devices through a control interface module block. If station parameters such as process variable, set point, and control

output are to be trended, an AO/L block is not necessary because the current values are obtained from the station exception report. The exception reports are on the loop without an AO/L block. Only a trend block (function code 66 or 179) is necessary.

 

Figure 80-2 shows how an auto bypass capable hard station is configured to operate on the remote SAC link of a CIO block using function code 221, function code 223, and function code 80 function blocks interfaced to CIO/SAC01 hardware.

 

Figure 80-3 shows how an indicating only hardstation is configured to operate on the remote SAC link of a CIO block using function code 221, function code 223, and function code 80 function blocks interfaced to CIO/SAC01 hardware.