Change In Tuning Parameters - Siemens SIPART PS2 Service Manual

Troubleshooting Procedures

3.7 Change in Tuning Parameters

3.7 Change in Tuning Parameters
The SIPART PS2 uses a control method called "pulse width modulation". This is a true
digital control method, where piezo valves, similar to very small solenoid valves, are used to
control loading and exhausting air, to and from the positioner. As such, tuning parameters
listed below are based upon this control method.
Note
Adversely Affected Valve Performance
The need to customize tuning parameters is likely compensating for another valve related
issue. Therefore it is recommended to resolve the root-cause valve issue instead.
Additionally, improper tuning values can severely affect valve performance, and thus
adversely affect the process.
It is recommended to make small tuning changes to prevent process upsets.
Adjustable Tuning Parameters Descriptions:
● [IMPUP] & [IMPDN]: Impulse Length UP and DOWN
– These tuning parameters are similar to gain. They represent the minimum time the
● [SSUP] & [SSDN]: Short Step Zone
– These tuning parameters are similar to integral action. Essentially there are two
● [PRUP] & [PRDN]: Prediction Up and Down
– These tuning parameters are similar to derivative. This predicts the movement of the
Note
Adjusting tuning parameters will overwrite the initialization values. To undo customized
tuning values, run initialization. See Initialization Procedure (Page 50).
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piezo valves will cycle; units are in milli seconds- ms. For example; if the value is
10 ms, the fastest the piezo valves will cycle is 10 ms, not any faster. Therefore, an
increase in these values will increase the gain response. Range is: 2.0 to 160 ms.
actions of the piezo valves- long pulses and quick/short pulses. The values are in
percent of total stroke. When the position of the valve is within this Short Step Zone of
the setpoint value, the positioner will begin the short pulses of the piezo valves. For
example, if the current short step zone is 10 % and the positioner is given a step
change from 0 to 50 %, the piezo valves are held wide open (long pulse) until the
valve gets to within 10 % of setpoint. Therefore, once the valve is at 40 %, the piezo
valves will produce short/quick pulses, to prevent overshoots. The smaller the value,
the faster the response.
valve. The smaller the number, the less prediction is used, thus faster response.
Range is 1 to 40.
PS2 Troubleshooting Guide
Service Manual, 03/2017, A5E36661550-AA