Rockwell-automation T8019 Trusted Process Control Algorithm Software P User Manual download pdf (Page 24)

Trusted

Process Control Algorithms T8019

Issue 8 Sep 07 PD-T8019 24

2.12. Analogue Value Slew

SLEW

OUT

RATE

The analogue value slew function limits the rate of change of the output value (OUT) to the maximum

specified by the RATE input. On initialisation, OUT is set to PV. Changes in the input (PV) will be

tracked by the output with the maximum rate of change. If the rate of change of PV is less than the

maximum rate, the output will immediately follow the input. PV is assumed to be in units, RATE is then

in units per second.

OUT

i.e.:

if PV > OUT

then

()







































×+= RATE,

OUTPVABS

MinTTOUTOUT

t1t1

2 else

()







































×= RATE,

OUTPVABS

MinTTOUTOUT

end if

Where:

is the current time (seconds)

is the time the algorithm was previously executed (seconds)

PV is the current input value

OUT

is the output value the time the algorithm was previously executed

RATE is the current RATE input value

All input parameters (PV and RATE) must be finite, i.e. not ±infinities or NaNs. Behaviour is not

defined for any other values. If RATE is negative, its ABS value will be used and the “param” error

counter incremented.

If an overflow condition occurs during the execution of the function, the function is to set OUT to its

previous value and increment the “overflow” error counter. If underflow occurs, the function is to set

OUT to its previous value and increment the “underflow” error counter.

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Rockwell-automation T8019 Trusted Process Control Algorithm Software P User Manual Page 24

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