Only on-off output with PID?

[Action22]

Hi,

 V700 with  V200-18-E3XB

Is it possible to have a PID only output at 0% or 100% and nothing in between? 

I am trying to do this to prevent a hardware component from chattering when it is not ran at 100%

 

I see in Visilogic function block software manual it says the following 

 

I have set the proportional band to 0 but i still notice that i am getting values in between 0 and 100 .

I've attached the project, any advice appreciated. 

52.vlp

[kratmel]

44 minutes ago, Action22 said:

Is it possible to have a PID only output at 0% or 100% and nothing in between? 

It is SLOW PWM output for PID.

Please use in FB's menu section PWM--> SCAN.

You can find in HELP how to operate PWM (0-1000 PID output=0-1000 PWM). Then your 0-100% PID output can operate ON-OFF controlled heater.

Duty Cycle for SLOW PWM must be set approx 2-40s ( for example Duty Cycle  in steps of 0.25ms  (400=1sec)) .

[kratmel]

If you do not need PID control,

Deadband Example.vlp sample code can be used for deadband control.

 

[Flex727]

17 hours ago, kratmel said:

If you do not need PID control,

Deadband Example.vlp sample code can be used for deadband control.

This is probably the best answer - a basic thermostat with hysteresis. Easy to implement and 100% reliable.

[Action22]

Great I will give this a try, appreciate the feedback!

[Action22]

I did make the change, however I notices that the temp fluctuates .4 c below and .7c above the setpoint. I tried change where my deadland was set but the range would not tighten. Any advice appreciated. 

[Joe Tauser]

By definition, Deadband Control is fully on or fully off.  There's no in-between, and you said in your initial post that you wanted to prevent hardware chattering.

That small of a fluctuation is really quite good for deadband control.  The range from deadband control can vary from +/- 1 degree to +/- 50 degrees depending on the thermal characteristics of the system.

You can't have it both ways.  If you want more accurate control  you'll need something that can utilize a PID loop properly and apply energy to the system in an analog fashion - somewhere between 0% and 100% with a one second or faster loop update.  This is what we use solid state relays for in a heating application.

Joe T.