USER’S MANUAL

PID Steady State Test [388]
In application situations where the feedback can
become independent of the motor speed, this PID
Steady Test function can be used to overrule the PID
operation and force the VSD to go in sleep mode i.e.
the VSD automatically reduces the output speed while
at the same time ensures the process value.
Example: pressure controlled pump systems with low/
no flow operation and where the process pressure has
become independent of the pump speed, e.g. due to
slowly closed valves. By going into Sleep mode, heating
of the pump and motor will be avoided and no
energy is spilled.
PID Steady state test delay.
NOTE: It is important that the system has reached a
stable situation before the Steady State Test is initiated.
Default:
Range:
Off
Off, 0.01–3600 s
Communication information
Modbus Instance no/DeviceNet no: 43373
Profibus slot/index 170/22
Fieldbus format
Modbus format
388 PID Stdy Tst
StpA
Off
Long, 1=0.01 s
EInt
During the steady state test the PID operation is overruled
and the VSD is decreasing the speed as long as
the PID error is within the steady state margin. If the
PID error goes outside the steady state margin the test
failed and normal PID operation continues, see example.
Default: 0
Range:
0–10000 in process unit
Communication information
Modbus Instance no/DeviceNet no: 43374
Profibus slot/index 170/23
Fieldbus format
Modbus format
389 PID Stdy Mar
Stp 0
A
Long, 1=0.01 s
EInt
Example: The PID Steady Test starts when the process
value [711] is within the margin and Steady State
Test Wait Delay has expired. The PID output will
decrease speed with a step value which corresponds
to the margin as long as the Process value [711] stays
within steady state margin. When Min Speed [341] is
reached the steady state test was successful and
stop/sleep is commanded if PID sleep function [386]
and [387] is activated. If the Process value [711] goes
outside the set steady state margins then the test
failed and normal PID operation will continue, see Fig.
69.
PID Steady State Margin [389]
PID steady state margin defines a margin band around
the reference that defines “steady state operation”.
[711] Process Value
[310] Process Ref
[389]
[389]
[387]
[388]
time
[712] Speed
Start steady
state test
Stop steady
state test
Normal PID
Normal PID
Steady state
test
Stop/Sleep
[341] Min Speed [386] PID