ATR244 control impulses too short for 3p valve

IvarsB · Post by **IvarsB** » 17/08/2021, 13:27

Hello,

We are using Pixsys ATR244 controller to control a valve for cooling - servo motor type control - Relay Q2 open, Relay Q3 close. The problem is that the control impulses from the controller sometime are too short and the valve does not react. The result is that the valve regulates OK for a while, but when the process starts to stabilize, the controller gives out short impulses and continues to do so even when there is a large difference between the SP and process. This happens until the SP for the valve is either 0 or 100%, then the valve starts to move to one end and then the problem starts from the beginning.

I do not see any specific setting for controlling the minimum impulse length. We tried increasing the valve move time (p_47) - actual is about 40 seconds, the setting was increased up to 150 - this did not help much. I also tried setting a negative Command delay (P_45) but that did not seem to create any change.

Are there any recommendation on how this could be fixed?

Post by **Pixsys tecnico 6** » 23/08/2021, 9:47

Good morning,
Have you tried using proportional band in parameter 75?
is used for valve modulation so that it is no longer ON/OFF.
You can try to set it to "10" (P.75) and set the parameter 79 in "Enab".
Doing so will have a modulation band +/- 5 from the setpoint set.

Best Regards,

IvarsB · Post by **IvarsB** » 23/08/2021, 13:34

Thank you for your reply.

Yes we are using PID regulation/proportional band. Maybe I did not explain the problem well enough:
When the regulation starts there is a big difference between process and setpoint, the regulator calculates that the valve position should be for example 50%, so it moves it from 0% to 50% and the impulse is long and this works well. And while the process is unstable, the controller calculates a large move for the valve and so the impulse is long and there are no problems.
The problems start when the valve position needs to move for example from 50% to 49% opening. The controller gives the move command, but the valve doesn't react because the impulse is too short. The next impulse is as short as the one before because the controller thinks the valve is at 49% and tries to move it to 48%, although the valve is actually at 50%. The valve is stuck until the controller thinks the valve should be 0%, because all the impulses are this short. Then the close command is activated permanently, the valve starts to move to close. At this point everything starts from the beginning.

Could you elaborate on parameter 79 Proportional Band Centered and how it could help the situation? I cannot find a clear description of it in the instruction.

Post by **Pixsys tecnico 6** » 23/08/2021, 14:33

The centered band simply centers the value entered in the parameter 75 "proportional band".
es:
Setpoint: 100°C
P.b.1: 10°C
the modulation band will be from 95°C to 105°C. without the centered band, modulation will be from 90°C to 100°C.

The parameter that might be appropriate for you is 78 [d.b.1]. Setting for example "1°C", you will have a +1/-1 band from the set point, where the controller will not execute any commands.

IvarsB · Post by **IvarsB** » 23/08/2021, 15:07

I tried setting the deadband P_78 but it does not help.
The regulator indeed does not try to regulate the output within the deadband range, but when it is outside of it the impulses are still very short.

Post by **Pixsys tecnico 6** » 23/08/2021, 15:19

You can try to raise the minimum percentage of power in par.87 [L.L.P.1], so as to extend the duration of the pulses. The higher the percentage, the longer the pulses.

IvarsB · Post by **IvarsB** » 23/08/2021, 15:32

I tried changing the parameter 87 but it does not seem to affect the impulse length but rather the minimum valve opening. If I set this value higher, the initial opening is larger, but when it starts to regulate the impulses are still short.

Post by **Pixsys tecnico 6** » 24/08/2021, 12:13

What is best to do is to return the controller to the factory data so as to set only the correct parameters to solve your problem.
Unfortunately, the parameter to set the minimum pulse length is not yet available in the ATR244. This is aviable in the DRR460.
link of product: https://www.pixsys.net/en/products/pid- ... ers/drr460
the following are the parameters to be set:

Group A [A.in.1]
- PAr.1 [SEn.1] > Analogue input configuration / sensor AI1 selection

Group C [cMd.1]
- Par.35 [c.ou.1] > "c.VAL."(Q1 and Q2) or "c.VAL.c." (Q2 and Q3)
- Par.47 [vA.t.1] > Valve time related to command 1 (declared by the manufacturer of the valve)

Group E [rEG.1]
- Par.73 [tun.1] > "diSAb"
- Par.75 [p.b.1] > 35% of the set Setpoint
- Par.78 [d.b.1] > 2% of the set setpoint
- Par.79 [p.b.c.1] > "ENAb"

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