Analogue value slew, Deviation alarm – Rockwell Automation T8019 Trusted Process Control Algorithm Software Package User Manual
Page 24
Trusted
TM
Process Control Algorithms T8019
Issue 8 Sep 07
PD-T8019
24
2.12. Analogue Value Slew
SLEW
OUT
PV
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
PV
i.e.:
if PV > OUT
t1
then
(
)
(
) (
)
×
+
=
RATE
,
T
T
OUT
PV
ABS
Min
T
T
OUT
OUT
t1
2
t1
t1
t1
2
else
(
)
(
) (
)
×
=
RATE
,
T
T
OUT
PV
ABS
Min
T
T
OUT
OUT
t1
2
t1
t1
2
t1
end if
Where:
T
2
is the current time (seconds)
T
t1
is the time the algorithm was previously executed (seconds)
PV is the current input value
OUT
t1
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.