What type of PID setup should I use?

[gusterminator]

Hi guys,
I am using a PID to control my brewery. Right now I have it controlling my Hot Liquor Tank. I have my TUN circulate threw a 50' coil that is submerged in the HLT. My temperature in the TUN is about 10 degrees lower than the HLT. If I use the TUN as PID input then it heats my HLT too much it's 30 gallons and takes a long time to come down. I'd like to use the HLT temp until it gets close and then switch to the tune.

any suggestions on what's the best way to control this system?

Thanks,

 

[seth350]

Hmmm...not quite sure if I am following you. Could you please explain more?
What is a TUN? What is it for? What is the 50' coil doing? How many temperature inputs do you have and where exactly is the sensor location? How are you heating the liquid? Is the heat on/off or proportional?
Your question really only makes sense to other brewers.
I don't brew, I just indulge....or used to. Lol

 

[gusterminator]

A Mash TUN is the pot that the grain is put in to. The Enzymes need the water or un finished beer to be held at different temperatures so the starches can be converted to fermentable sugars. I continually pump the liquid from the mash TUN threw a coil that is submerged in the Hot Liquor tank......which is just another bigger pot full of water to hold the desired temperature. By changing the temperature in the HLT it changes my Mash TUN temperature. During recirculation I have heat lose of around a 10 degree difference.
The coil is like a heat exchanger. I have a temp sensor in the HLT thermo well and one in the Mash TUN also a thermo well. I am heating the liquid in the HLT with an electric Boil coil around 6000 Watts. I have it hooked up to a 40A 4-20 solid state relay. I am controlling it with a Compact Logix 5434 processor programming with RSlogix 5000. I am using the PID instruction not the PIDE.
I was wondering if I would have closer control using Cascade or a ratio setup. I would like my mash temp to be dead on......right now I control the HLT temp. I am using P and I right now no Derivative.

Hope this helps.....and thanks for the reply.

 

[manex]

to gusterminator,


I also works in the brewery, try to specify first how big is your lauter TUN and how good is your pipe system, that is, is it well insulated? as per experience, you should have an 85 degrees HTL before you mash.

Do not rely on your PLC if you are mashing unless you already considered other factors like your rake, your false bottom, and your lauter tun itself. and always have a hand held temp meter because sometimes the temp that your sensor(s) readings is just the part where you installed, the other parts or area may or might not have the same temp even you raked them properly.

It is also worth to note that it is very hard to spot on your temp in the tun even with the help of PLC. If I may, try to have another pipe of De-aerrated water (cold as 20 deg) (injected with CO2) to compensate whenever your temp shoot rocket high. have a tee connection in the pipe where your hot water from HLT runs AND before your flow meter.

in terms of PID, it is hard to give you some example because it needs the details of the pipe system you are using. it also worth to note if your pipe systems are well-insulated because as per experience, even how great your PLC program is, but if you deliver that in real world, potential difference and all those stuffs will still give you a head ache. I have four temp reader in my tun and still I have a hand held temp meter during mashing. Though my PID works good (ml1100) but we still have to check them from time to time manually, until we spurge and transfer the wort to brewkettle.


"If the power of love overcomes
the love of power, the world will know PEACE"

 

[gusterminator]

Thanks for the input.....this is just a home system. I have made around 15 to 20 batches of beer that turned out great! I'm very happy with my system. I'm looking for information on how to set up ratio or cascade using the PID block in RSlogix 5000. Right now I control the HLT temp for my steps so I set the PID 10 degrees higher than the temp I want in my Mash Tun.....This is fine and works but I do get a 3 degree off set higher or lower In the TUN at times. I would like to use the HLT for initial temp target.....then when the Mash Tune gets within 3 degrees Id like it to switch and use the Mash TUN temp probe instead of the HLT temp probe......
This is just my idea......I'm looking for some suggestions.....on how I could attain this.

Thanks.

 

[seth350]

Thanks for explaining. So when you say you get a 3 degree offset in your TUN at times. Would you say that it is always 3 degrees out one way or the other or is it always spot on and only deviates at specific events during your process?

If the answer to the first question is yes then the PID is not tuned to your process.
If the answer to the second question is yes then your PID is tuned "properly" but could benefit from inserting a feedforward/bias. Almost always when implementing feedforward another sensor/attribute needs to be brought into the control model. That being another thermocouple, flow rate, heat input, be it field or calculated.

In the example of heat input for feedforward, I monitor the voltage and amperage of a DC Rectifier and calculate BTU input. That is then fed into a PID as feedforward that controls a proportional cooling valve to keep a 4,000gal tank at 70degF.

Basically, because the temperature is only monitored in one spot of the tank, the time constant is incredibly high. By the time the sensor detects a rise, the tank is already saturated with heat. At that point is when the PID responds to open the cooling valve.
By knowing when the rectifier is on and how much heat it is putting in the tank, I can give the PID a "head start".

That may not make sense. I'm not the best when explaining. Hopefully it brightens a light bulb for you.

 

[gusterminator]

My PID will hold my HLT pretty much with in 1 degree. I recirculate the water in the HLT continuous to keep the heat even thought the kettle so my temp reading is giving me an accurate reading.
I believe a feed forward method may help me. The second sensor would be my Mash TUN sensor. I'm looking for a Ladder Logic example of a feed forward system. I'm not sure how to implement this into my program. I have ideas! Would I send the out from the Master PID into the in of the second PID? This is where I need help. If I saw an example I could figure it out I think.

 

[g.mccormick]

You should use cascaded loop. The tun loop would send a temp set point to the hot loop. The tun loop output should be bounded so that the settings sent to the hot loop are requested tun set point +/- 5 degrees or so.