PID or differential gap

Dunnsept

I am going to make a temperature controller for a chest freezer (for lagering beer)
I will build it with an SX protoboard. my question is more of a generic one for your process control guys,
should I try to go for PID on it.· most of the commercial (cheaper) controllers have a band of about 3.5
degrees. the expensive ones are 1 degree. 3 or 4 degrees either way isn't going to matter much.
I guess I could go with something like P or I, or P and I instead of the full PID. The chest freezer is
obviously well insulated, but will sit in an un-insulated (as of now) barn
suggestions and/or tips appreciated. pics to come once it's finished..· oh.. and I'll be using a 10A SSR
for this too

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stand back! I have a slide rule and I know how to use it!

sam_sam_sam

Dunnsept·


The chest freezer is obviously well insulated, but will sit in an un-insulated (as of now) barn

I Am a A/C Tech For Many Years

One think to think about is that if the barn dose not have good air flow you will have problem with your· Chest Freezer· The compresor will have work VERY hard to Get Rid of All of the Heat·that in the Chest and the Heat From the Compressor and the heat in the·barn·Meaning that it will RUN ALL THE TIME And not meet The temp iin side of the chest freezer box will not be meet and so it will run all of the time
The life of your compressor·will be·shorten

One more thing to think about is that you DO NOT want the Compressor to Run and Shut OFF and then ReStart for at LEAST FIVE MINUTES
Or longer that depends on the compressor and how long it take for the compressor to want to start again·most are at least five minutes
You also want this if the power gose out and then come right back·ON you will·want this delay
·If you do·not·follow this·the life of your compressor·will be·shorten

This not a bad ··to have a the Temp controled with a·SX ProtoBoard

·Most of the commercial (cheaper) controllers have a band of about 3.5 degrees. the expensive ones are 1 degree. 3 or 4 degrees either way isn't going to matter much ...............They also have a Five minutes delay ....................

If·I where builting this controler

This is how i would go about it

One

When the Basic Stamp frist power up wait Five Minutes

Then start if temp has not been·meet then

Check temp when the temp has been meet·· Let say at·35 *F

·Then Turn OFF

Check Temp when temp has gone to 36 *F

Has Five minutes past

If so Then restart

If not wait for Five Minutes

Two

I would have an alarm that would sound if the box Temp has gone to let say 40·*F

Three

I would also have an alarm to sound if your Barn Temp is any higher than 90*F

This is Just Some· ·s of What Can Be Done


·Please let me how this project come along i would like to see what you come up with

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··Thanks for any··that you may have and all of your time finding them

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Sam

Post Edited (sam_sam_sam) : 4/25/2007 3:11:11 AM GMT

Dunnsept

thanks Sam.. that's great info. I had not thought about a delay or an alarm

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stand back! I have a slide rule and I know how to use it!