Troubleshooting Procedures
3.10 Erratic Feedback
PS2 Troubleshooting Guide
Service Manual, 03/2017, A5E36661550-AA
25
There are two settings for the PS2 deadband:
"Auto" or a fixed numerical value.
● When configuration parameter "DEBA" = "Auto", the deadband value is dynamic and
changes per the process conditions. In other words, the deadband value changes if
stiction or oscillation is detected. For example, the deadband value will increase when
mechanical issues are detected. Additionally, the PS2 will periodically decrease the
deadband value to try and achieve precise valve positioning. The deadband value
changes in 0.1 % increments.
● Thus, only a fixed deadband value can be too small.
● Too small a deadband can cause valve oscillation and indicate:
○ Too much stiction; see Stiction (Page 36).
○ Loose linkage; see Loose Linkage (Page 29).
● From AUT or MAN mode, press
button for 5 seconds. Now observe the parameter
name in the lower right corner.
● Continue to press the
button until "DEBA" parameter is reached.
● Use
and/or buttons to decrease deadband value or change to "Auto".
● To return to Automatic mode, press and hold the
button for 5 seconds.
● The unit will now be in Manual mode.
● Press the
button one time to return to Automatic mode.
The PS2 is providing a false and jumpy feedback signal, but the actual valve position is not
moving.
First, rule out field wiring and power supply:
Does the large number on the local display represent the jumpy and false signal read on the
4/20 mA feedback?
● Use an independent power source and current meter to isolate the field wiring by
powering up the feedback card locally.
– 24 V DC positive connected to terminal 61.
– Put meter in current mode and connect positive to terminal 62.
– Connect wire of current meter to 24 V DC negative, according to Wiring (Page 43).
● If erratic feedback is gone, then issue is with field wiring or original power source.
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