PID control combined with SSR

Discuss tuning PID coefficients to maximize system efficiency.
Post Reply
bergerrings
Posts: 41
Joined: Wed Feb 08, 2012 9:48 pm
Bot?: No

PID control combined with SSR

Post by bergerrings » Sun Aug 12, 2012 10:59 pm

This may be an obvious question but I can't seem to make sense of it.

I wish to control two pumps for circulating cooling and heating fluids amongst a few fermenters that I have been building. I will be using the BCS for this purpose and I have the pumps connected via SSRs.
My question is, how is it possible for the BCS to implement proper PID control (varied output signal, ie varied voltage ) when the output signal must go through an SSR which can only be on or off…?
Does this just mean that the ‘PID’ cycles between on and off within a specified time range? So as the target is approached the PID cycles closer and closer to the minimum cycling period?

Thanks in advance for your help!

bergerrings
Posts: 41
Joined: Wed Feb 08, 2012 9:48 pm
Bot?: No

Re: PID control combined with SSR

Post by bergerrings » Wed Sep 05, 2012 11:07 pm

Any thoughts anyone....?

User avatar
JonW
Site Admin
Posts: 1622
Joined: Sun Jul 18, 2010 7:51 am
Bot?: No
Location: Huntington Beach, CA
Contact:

Re: PID control combined with SSR

Post by JonW » Thu Sep 06, 2012 8:12 am

There's a huge difference in the performance of mechanical relays and solid state relays. Your thoughts about "on" or "off" are really only applicable to mechanical relays, because of how slow they switch. Alternatively, the SSR can switch on and off in micro seconds. Because of this, a very fast switching of on and off (pwm) has the basic effect of cutting the total current output. Cutting the current is equivalent to turning the temperature down on the heating element.

Post Reply

Who is online

Users browsing this forum: No registered users and 0 guests