TM172 ThreePointActuator control

[lionginas_elekt]

Hello.

In a HVAC project I use 3 point actuator control with PID and ThreePointActuator blocks.

ThreePointActuator block takes from PID difference of PV_current_value and PV_set_point and

generate Close or Open pulses. I wander why those pulses are very short by lenght. It results

that PID saturated to 100 % but the valve is open too little. I inserted TON timers to extend close

and open pulses, but I am not sure is it right way to use.

Appreciate any comments,

Best regards.

[Bastian_Schmitz]

Hi,

Normally you could directly connect the Digital Outputs for the actuator directly on the block. If the time puls is to short, then the value of uiMaxRuntime could be the problem. The Resolution of this value is 0.1s and not 1s. If you have a actuator which has a travel time from open to close with 90s you need to enter the value 900.

[lionginas_elekt]

Thanks for reply. uiMaxRuntime is correct. To figure out where is problem I did simulation with PID and ThreePointActuator. The first I did XCalibration = true, xClose go TRUE for 30 seconds (uiMaxRuntime = 300).

Then I set rPV and rSetp difference and wait for uiControlSignal for saturation to 1000. xOpen generated series of shot pulses. I am right if at this point I go to xManualMode = 1 (rManualValue = 0) xClose need to be

go TRUE the same time 30 s. But I see there only 5-6 sec. 

[Bastian_Schmitz]

Did you use the AFB in a Timed or in a Background Task? I did not double check it, but I expect that the block should be run in a timed task. 

[Bastian_Schmitz]

The input uiControlSignal expect a value between 0...10000 (0,01%). That is a little bit strange because the PID gives as output 0....1000. I think that is the main case of your problem. I need also several time to read correctly this point in the documentation ?!?

[lionginas_elekt]

In my case they are equal. The first one is PID output ranged 0...1000 and scaled 0.1% and the

second one is ThreePointActuator input ranged 0.....10000 and scaled 0.01%. Do you think it is problem.