A SIPOS 5 Professional actuator ran with no alarms, accepting a 4-20 mA command signal, yet behaved bizarrely: the command had to change by about 15% before it would move, and then it moved only about 5% and stopped, with a large deviation between command and feedback. For this kind of extreme sluggishness, the discussion narrowed the suspects down to five — and the first one proved to be the root cause.
An engineer who had commissioned many SIPOS Professional units delivered the decisive experience: once after commissioning, the LCD showed "ready" but the actuator could only travel 10% of its stroke. After a long hunt, they found the feedback potentiometer had been disturbed by the construction crew during their commissioning. The SIPOS manual clearly requires that, before commissioning, the feedback gear be brought to the specified position — at which point the resistance between potentiometer taps 1/2 and 2/3 should be equal. If the deviation is large, exactly this kind of fault appears. Restoring the feedback gear and re-commissioning cured it.
This root cause matches the present symptoms (sluggish response, moves a little then stops, large feedback deviation) perfectly, and deserves to be the first check.
If the feedback potentiometer checks out, continue in order:
1. Dead band setting: the SIPOS configuration/commissioning menu contains a dead-band item — verify it has not been set excessively large; a large dead band naturally ignores small deviations;
2. Remote-control mode parameter: verify the remote control type is correct (it should be PosCntr CurrInp, i.e., position controller with current input) — with the wrong mode the command is interpreted incorrectly;
3. Signal interference: is the command cable shielded? Is the shield grounded at one end (control-room side)? Try grounding the signal negative locally and observe; another trick is shorting terminals 15 and 18 to unify signal ground with actuator ground, eliminating bias from ground-potential differences;
4. Signal board fault: after eliminating the above, suspect the signal board. Board replacement has a rule: before swapping, upload the actuator's parameters to a laptop via the communication port with the dedicated software; after fitting the new board, download the file back, then run the ADJUST setting — otherwise all parameters are lost and everything must be set from scratch.
The triad "sluggish, moves a little then stops, large feedback deviation" points first at the feedback path: the feedback gear position and a tampered feedback potentiometer are the classic trap on SIPOS-class actuators. After the feedback path, work through dead band → mode → interference → board swap. One reminder earned through painful experience: with intelligent actuators, always upload and save the parameters before changing any board.
