Deadband Too Small - Siemens SIPART PS2 Service Manual

Troubleshooting Procedures

3.9 Deadband Too Small

● If deadband value is too large for the application, the PS2 is compensating to prevent
valve oscillations. These valve oscillations could be:
– Too much stiction; see Stiction (Page 36).
– Too many step changes from process controller. This is a process control loop issue.
– Loose linkage, see Loose Linkage (Page 29).
Change Deadband Setting:
● From AUT or MAN mode, press
name in the lower right corner.
● Continue to press the
● Use
● To return to Automatic mode, press and hold the
● The unit will now be in Manual mode.
● Press the
3.9 Deadband Too Small
The deadband of the PS2 is the area around setpoint when the PS2 stops working to get
closer to setpoint. For example, if the deadband value is 0.1 %, and the setpoint is 70 %, the
PS2 will work the piezo valves to get within the following position range: 69.9 % to 70.1 %.
Thus, the PS2 will continuously work to get within this deadband range. However, if the
mechanics of the actuator and/or valve cannot achieve this precise position, the PS2 will
continuously hunt or oscillate around the setpoint position.
24
Discuss issue with operator and/or plant process engineer.
NOTICE
Valve Oscillations
Too small a fixed deadband value can cause valve oscillations, see Dead Band Too
Small (Page 24).
and/or buttons to decrease deadband value.
button one time to return to Automatic mode.
button for 5 seconds. Now observe the parameter
button until "DEBA" parameter is reached.
button for 5 seconds.
PS2 Troubleshooting Guide
Service Manual, 03/2017, A5E36661550-AA