How do PIDs/SSRs work?

Pardon my noob-i-ness but I'm just trying to understand the relationship between PIDs and SSRs and how they function in a HERMS system. I'm not really sure how the SSR relates to the process and what it does. I've heard of running multiple SSRs for different functions, do you need seperate PIDs too?

Would someone be able to elaborate how these work and provide examples of them in a system?

PID is basically an intelligent controller that provides on/off switching with a lot of flexibility. The SSR takes the on/off signal from the PID and switches higher amperage loads. The electronics of the PID can't handle the high currents of heating elements. The Solid State part of SSR is what makes it able to switch on and off very quickly without being destroyed like a mechanical relay.

The PID is like your brain and the SSR is like a bicep muscle.

The SSR would be the switch for a heating element in your HLT. The PID would provide the control signal to the SSR based on temperature data from a probe in the HLT.

So the SSR has the ability to control the 'load' or 'amount of power' being sent to the heating element and the PID tells the SSR just how much power to send and when or just when? What I mean is, I've read that 50% on a 1 minute set interval would result in 30 seconds on and 30 seconds off, is that on at full power right or is it (does it have the ability for) limiting wattage (i.e. 50% of 5500 = 2750 watts)? Is it essentially just setting the timing of the power being sent?

Sorry if I confused this at all, this is all new to me!

It's always on or off, full power but it creates duty cycles to limit the effective power. I'm pretty sure that's how the power setting on a microwave works too.

The PID and SSR could also be used in a HERMS brewery to control the mash temperature by controlling a pump that recirculates your mash water through a coil in your HLT.

A pid controls a low voltage circuit(typically dc) like 5 volts, not enough to do anything. Except to switch something that can do something(the ssr) which you can get in all manner of capacities rated based on amps/voltage and control voltage(ac vs. dc). The ssr is what allows a low voltage control circuit to control and switch a high-voltage work-doing circuit.

So one can't work without the other(and do anything meaningful). You can also control multiple circuits with a single control voltage from a single pid(or in my case single out circuit from the bcs).

I think the bicep metaphor is speaking to the idea that the actual power that is being controlled is going through the ssr, but the PID tells the ssr when to let that power flow.

Sawdustguy said:

The PID and SSR could also be used in a HERMS brewery to control the mash temperature by controlling a pump that recirculates your mash water through a coil in your HLT.

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If you are using an SSR and PID in a HERMS, you will want it to control the temp of the HLT for the HEX. HERMS generally is a constant recirc., and in a HERMS you need temp. control on the HLT anyway so the PID/SSR is best used there.

I agree with pol. In fact, I recently found that whole "turn the pump on and off" thing in the WIKI as "the" way a HERMS works and felt compelled to do some editing. I feel like a fraud doing so since I have no temp control automation in my brewing as of yet. If anyone wants to clean it up, be my guest.

Bobby_M said:

I agree with pol. In fact, I recently found that whole "turn the pump on and off" thing in the WIKI as "the" way a HERMS works and felt compelled to do some editing. I feel like a fraud doing so since I have no temp control automation in my brewing as of yet. If anyone wants to clean it up, be my guest.

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ARE YOU SERIOUS, the WIKI sayes that HERMS runs based on turning the pump on and off? Wow... yeah bad idea. The pump will get hammered with on/off cycles.

You will not be controlling the mash temp very well becasue you will not be contantly recirculating it to keep it homogenous.

Not to mention the fact that you STILL need a temp. controller on the HLT, so why even mess with a controller on the pump?

The WIKI is wrong.

Well, I mean I did clean it up but someone should check my work at minimum. The other problem was that there was absolutely no mention of direct firing as a method of mash control. You'd think with the popularity of Brutus 10, it would have been mentioned in passing. Hey, no harm... it's a fluid document.

Guys, by the way, Chris Colby wrote an article in BYO a few years back (the ABCs of brewing systems issue) that described a HERMS as switching a valve that controlled wort flow. He said that the mash temperature was controlled by either recirculating the wort back to the mash tun, or recirculating it through the heat exchanger to the mash tun. He said that the temperature of the heat exchanger stayed constant, the recirculation was constant, and the only variable was whether the wort travelled through the heat exchanger. That seems like an odd approach to me, though. It seems like it would be easier to automate an electric heating element than a valve.

stoutaholic said:

Guys, by the way, Chris Colby wrote an article in BYO a few years back (the ABCs of brewing systems issue) that described a HERMS as switching a valve that controlled wort flow. He said that the mash temperature was controlled by either recirculating the wort back to the mash tun, or recirculating it through the heat exchanger to the mash tun. He said that the temperature of the heat exchanger stayed constant, the recirculation was constant, and the only variable was whether the wort travelled through the heat exchanger. That seems like an odd approach to me, though. It seems like it would be easier to automate an electric heating element than a valve.

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People are always making things MUCH more difficult than necessary.