Time Proportional Control Example?

[brooksware2000]

Time Proportional Control is pretty much a slower version of PWM where the duty cycle is varied by on and off time. For example, if the time span is 10 seconds and I want 90% on time then, that converts to 9 seconds on and 1 second off.

So, the output of the PID routine would span between 0 and 10 seconds for on vs. off time. To accomplish this, I need a way to make a guess as to whether the SSR should be on or off based on the output of the PID loop.

See this link, this link, and this link for the Arduino example.

Thanks for the help,
Curtis

[Jerson]

Hello Curtis

Welcome to the forum.

Your problem can be broken down into 2 parts
1 - caluclate the value of output power via your PI routine
2 - convert this power to a time value

From your question, I guess, you have no issues with point 1

Assume you have power going from 0 to 100% corresponding from full off to full on. This can be converted to time thus

If the cycle time Tcyc you specified for your controller is - let us say - 10 seconds

On time will be
Ton = (Tcyc * Power) / 100

With this, you will get a Ton ranging from 0 - 10 seconds

Now, to control the duty cycle of your heater using this value, you can do this
Tvar var word

Tvar is a variable that runs from 0 to 10 seconds.


Tvar = Tvar + 1
if Tvar >= 10 then Tvar = 0 ' roll over

if Tvar < Ton then
gosub HeaterOn
else
gosub HeaterOff
endif

I hope this will help you


Oh, I forgot to add that you need to have the code above run at a fixed 1 second rate to get correct results

[brooksware2000]

Hello Curtis

Welcome to the forum.

Your problem can be broken down into 2 parts
1 - caluclate the value of output power via your PI routine
2 - convert this power to a time value

From your question, I guess, you have no issues with point 1

Assume you have power going from 0 to 100% corresponding from full off to full on. This can be converted to time thus

If the cycle time Tcyc you specified for your controller is - let us say - 10 seconds

On time will be
Ton = (Tcyc * Power) / 100

With this, you will get a Ton ranging from 0 - 10 seconds

Now, to control the duty cycle of your heater using this value, you can do this
Tvar var word

Tvar is a variable that runs from 0 to 10 seconds.


Tvar = Tvar + 1
if Tvar >= 10 then Tvar = 0 ' roll over

if Tvar < Ton then
gosub HeaterOn
else
gosub HeaterOff
endif

I hope this will help you


Oh, I forgot to add that you need to have the code above run at a fixed 1 second rate to get correct results

Very good! You made it look so simple. I'll be sure to post the code once it is all worked out.

Thanks,
Curtis

[cncmachineguy]

Yup, as I said, my lack of understanding. Thank you for the links Curtis. It may just be time for me to start playing with PID. Good luck with your project