FC 53 - Executive Block (COM)

 

The executive block for controller modules defines several

variables that affect module operations. The executive block

for controller modules has 15 outputs (blocks 240 through

254).

 

 

Outputs:

Blk

Type

Description

240

B

Start-up in progress: logic 1 for first 15 secs of module execute mode; then logic 0

241

B

Nonvolatile random access memory in initialize mode: logic 1 when switch is closed1

242

B

State of general purpose switch1

243

R

Last control cycle time (secs)

244

B

Valid time received from bus module2

245

R

Hours (0 to 23)

246

R

Minutes (0 to 59)

247

R

Seconds (0 to 59)

248

R

Calendar Year (0 to 99)

249

R

Calendar Month (1 to 12)

250

R

Calendar Day (1 to 31)

251

R

Calendar day of the week: Sunday = 1, Monday = 2, etc.

252

R

Revision level

253

R

Nonvolatile random access memory utilization (%)

254

R

Random access memory utilization (%)

 

NOTES:

  1. Refer to appropriate controller instruction.

  2. The time received from the bus module increments every second. If the BIM does not send the time to the controller, the block outputs reflect the time relative to the controller reset. Midnight (or module reset) equals: hours equals zero, minutes equals zero, and seconds equals zero.

 

Specifications:

Spec

Tune

Default

Type

Range

Description

S1

N

0

B

0 or 1

Exception reporting time units:

0 = seconds

1 = minutes

S2

N

4

I

0 - 255

Minimum exception report time (250 msec increments)

S3

N

240

I

0 - 255

Maximum exception report time (increments dependent upon S1)

S4

N

2.000

R

Full

Significant change parameter loop reports (% span)

S5

N

1.000

R

Full

Alarm deadband high and low reports (% span)

S6

N

1.000

R

Full

Alarm deadband deviation reports (% span)

S7

N

25

I

0 - 255

Computer watchdog time-out interval (2.56 sec increments)

S8

N

4

I

1 - 255

Module bus update time (same PCU 250 msec increments)

S9

Y

25

I

0 - 255

Minimum cycle time algorithms (10 msec increments)

S10

N

0

I

0 - 255

Block address of configuration lock:

0 = unlock

1 = lock

S11

Y

10.000

R

Full

Defines maximum derivative gain for PID

S12

N

0

I

0 or 1

External reset for PID function block:

0 = normal

1 = external reset

 

 

53.2  Explanation

 

Specifications:

 

S1 - TUNIT

(Time units) Specification S1 defines the time units for the

maximum exception report time (S3). When S1 equals zero,

the units are displayed in milliseconds. When S1 equals one,

the units are displayed in minutes.

 

S2 - MIN

(Minimum exception report time) Specification S2 defines

the minimum interval between updates of information sent

on the INFI-NET from executive report blocks. Exception

reports are not sent on the loop at each minimum exception

report interval unless a value has changed more than an

operator defined significant amount (S4) since the last exception

report. Exception report time can be set in 250 millisecond

increments with the default set to one report per second.

 

S3 - MAX

(Maximum exception report time) This specification defines

the maximum interval between updates of information sent

on the loop. If the value of a point does not exceed the significant

change (S4) over this (S3) period of time, a report of its

current value is sent on the INFI-NET after this time period.

Exception report time can be set in 250 millisecond increments

when S1 equals one, or one minute when S1 equals

zero. The default value is one report per minute.

 

S4 - SIGCHG

(Significant change) Specification S4 defines the percent of

span a point value must change to cause an exception report

to generate.

 

S5 - ALRMDB

(Alarm deadband high and low reports) Specification S5

defines the alarm deadband in percent of span for all the high

and low alarm reports on the module specified. Alarm deadbands

prevent excessive alarm reports when values are hovering

around the alarm limit.

 

S6 - DEVDB

(Alarm deadband for deviation reports) This specification

defines the alarm deadband in percent of span for all deviation

alarms. Deviation alarms apply to control station blocks

only (function codes 21, 22 and 23).

 

S7 - COMPWD

(Computer watchdog time-out interval) The computer

watchdog time-out interval is an interval used to time computer

communications when a station (i.e., control loop) is

under computer control. Timing starts with a computer OK

message and station variable settings. For example, when the

station switches from manual to computer control, the message

goes to the computer which generates an OK message

and initiates timing. If the elapsed time between OK messages

exceeds the value of S7, the timer times out. The value

of S15 (computer watchdog time-out option) determines the

control mode of the station. If the computer replies to a module

message before the interval is over, the timer resets itself

and begins timing with the next communication. The interval

is in 2.56 second increments with a default value of 64 seconds.

 

S8 - MBUPD

(Module bus update time) Specification S8 defines the execution

rate for all module bus inputs in the same PCU. Module

bus update time is selected in 250 millisecond increments

with a default value of one update per second. Inputs and

outputs to the field synchronize with the module execution

rate. Each time a module updates, it receives a new input

and transmits a new output to the field. Bus and loop traffic

are asynchronous with the module execution rate. Values

from the bus and loop are stored in buffer blocks (e.g., digital

input over the loop function code 42).

 

S9 - CYCTIM

(Minimum cycle time for control algorithms) Specification

S9 defines the minimum cycle time for control algorithm execution.

Minimum cycle time is selected in ten millisecond

increments with a default value of four execution cycles per

second. Minimum cycle time in controller modules is normally

set at a maximum of four cycles per second because of

the high noise rejection of the input filters in the analog input

circuitry. An IMQRC01 Quick Response Controller is available

for faster response. Quick response controllers can execute

control algorithms at a rate of ten cycles per second.

 

S10 - CBFLOK

(Configuration lock) This specification can lock the configuration

of the module. Once a configuration is locked it cannot

be unlocked. To change a locked configuration, the module

must be initialized and reconfigured. A block address of zero

is unlocked and a block address of one is locked. Any block

whose output is boolean may be used.

 

S11 - Kd

(Maximum derivative gain) Specification S11 is the maximum

derivative unit step response for all PID function blocks

in a module. The default value is 10.000.

 

S12 - XRES

(PID external reset option) This specification affects all

function code 18 (PID error input) and 19 (PID - PV and SP)

blocks in the module or in a segment of an IMCOM04 module.

When the external reset activates, the module does two

internal checks. It first checks to see whether control is proportional

and integral or only proportional. It then checks the

external reset option.

 

For proportional only control:

If S12 = 0, the internal memory will not track.

If S12 not 0, the internal memory tracks the input to the block.

 

For proportional and integral control:

If S12 = 0, the internal memory does not track.

If S12 = 1 and track input = current output, internal memory does not track.

If S12 = 1 and track input ยน current output, the internal memory tracks the track input despite the status of the track and release flag.

 

 

This function prevents reset windup of a controller. Reset windup can occur in any system. The most common occurrence of reset windup is in batch control systems where controllers may be monitoring control variables but not performing any control action during the current step. The controller receives the signal, takes corrective action but sees no result, so it tries to correct the error again. Since the controller receives no results from its control action, it continues to try to correct the error. When the controller does go to another step of the process, it winds up beyond the value of the controlled variable and loses control. The external reset option enables the controller to be reset (zeroed) while it is not being used for control functions.

 

 

 

Outputs:

 

240

(Start-up in progress signal) When start-up is in progress,

output block 240 is a logic 1 for the first 15 seconds the module

is in execute mode. When start-up is successful, output

block 240 is a logic 0 and remains logic 0 while the module is

in execute mode.

 

241

NVRAM mode indicator) Output block 241 is a logic 1 when

the nonvolatile random access memory (NVRAM) hardware

switch is closed. To initialize NVRAM, the hardware switch on

the module must be set to the open position, then returned to

the closed position after initialization.

There are two controller boards currently in use. The NVRAM

switch is in a different position on each board. Table 53-1

shows the board numbers and the NVRAM initialization

switch numbers. Check the part number on your board to

determine which board you have. Refer to the appropriate

instruction manual for switch locations on that board.

 

 

242

(State of general purpose switch) Output block 242 is a

logic signal that reflects the state of a general purpose hardware

switch on the module. A zero equals closed and a one

equals open.

 

243

(Last control cycle time; in seconds) Output block 243 displays

the length of the last completed control cycle. Control

cycle time consists of:

 

A/D conversion of all inputs (~3 milliseconds)     +

execution time of algorithm                                    +

D/A conversion of all output (~3 milliseconds)     +

wait time (if any)

 

244

(Valid time flag) Output block 244 is a flag (zero or one).

This output represents which mode of time is displayed by

output blocks 245 through 251.

0 = Beginning of time. When output block 244 equals

zero, the time blocks 245 through 251 represent the module runtime from the last reset, starting at

hours, minutes, and seconds equal zero.

1 = System time. When output block 244 equals one,

the time blocks 245 through 251 represent the system

time.

 

245

(Hours) Zero to 23.

 

246

(Minutes) Zero to 59.

 

247

(Seconds) Zero to 59.

 

NOTE: Firmware revisions before July 1986 do not support outputs 248 through 252.

 

248

(Calendar year) Zero to 99.

 

249

(Calendar month) One to 12.

 

250

(Calendar day) One to 31.

 

251

(Day of the week) One to seven.

Sunday = 1

Monday = 2

Tuesday = 3

Wednesday = 4

Thursday = 5

Friday = 6

Saturday = 7

 

252

(Hardware revision level)