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Old 01-10-2014, 03:58 PM   #1
wuttheheeck
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Default PID reading wrong temperature

I am on the final stages of my herms system, the only thing holding me back is these dam temperature sensors.

I am using a mypin Ta4 style PID controller with a 2 wire PT-100.

Using this diagram I have jumped the terminals from 7-10 and 8-9


My PID is registering a temp more than 100* off form actual temperature.

Is there any way to calibrate a PID and tell it what 32* or boiling is?

Running out of ideas here,
Thanks

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Old 01-10-2014, 04:07 PM   #2
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I can only tell you that there is another thread here somewhere breaking down the exact wiring configuration for a two wire pt-100....once its right you'll find there's no calibrating necessary....
I can across the other thread while searching "my pin and pt-100" together.

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Old 01-10-2014, 04:10 PM   #3
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http://www.homebrewtalk.com/f170/myp...sensor-409045/
This might help....
You did set the pid thermocouple settings to the pt-100 right? They are set up for a thermocouple and not an rtd sensor out of the box... directions to change it are on the instruction sheet... at least that's were I found them.
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Old 01-10-2014, 04:46 PM   #4
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Should I use PT mode in my pid or use a RTD mode. From what i read on other forms, most PT-100 use 3 wires to account for line resistance.

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Old 01-10-2014, 05:05 PM   #5
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Quote:
Originally Posted by wuttheheeck View Post
Should I use PT mode in my pid or use a RTD mode. From what i read on other forms, most PT-100 use 3 wires to account for line resistance.
Rtd if thats what you have.... my rtd sensors are three wire pt-100's
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Old 01-10-2014, 07:07 PM   #6
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Update

i am within +/- 5 degrees when i am using the K setting for input and only using terminals 7 and 8

about to run a boil test, more updates to follow

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Old 01-10-2014, 07:55 PM   #7
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Quote:
Originally Posted by wuttheheeck View Post
Update

i am within +/- 5 degrees when i am using the K setting for input and only using terminals 7 and 8

about to run a boil test, more updates to follow
That's odd...I thought K was for thermo couples not rtd sensors?
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Old 01-10-2014, 10:37 PM   #8
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you're right. No luck with it on K setting. I've tried jumping the additional terminals like many forums suggest and that doesn't give me any help.

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Old 01-11-2014, 12:18 AM   #9
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If your sensor was wired to pins 7 and 8 then your wiring was indeed correct.

Can I ask where you got your sensor? 2 wire RTD probes (pt100 is a type of RTD) are not all that common, typically 3 wire for hobbyist level gear, and if you bought it from a chinese source on ebay there's a chance it might actually be a type K thermocouple!

When you say no luck with the K setting you had a value from it though? These can be very out at boil, I recently did a calibration on my PID setup in work and it was 8C (14F) out at boiling temperatures...

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Old 01-11-2014, 12:44 AM   #10
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Quote:
Originally Posted by big_len View Post
If your sensor was wired to pins 7 and 8 then your wiring was indeed correct.

Can I ask where you got your sensor? 2 wire RTD probes (pt100 is a type of RTD) are not all that common, typically 3 wire for hobbyist level gear, and if you bought it from a chinese source on ebay there's a chance it might actually be a type K thermocouple!

When you say no luck with the K setting you had a value from it though? These can be very out at boil, I recently did a calibration on my PID setup in work and it was 8C (14F) out at boiling temperatures...
I was getting a positive reading while only on the 7-8 pin and set as a K. I did buy it exactly how you said, it was cheap (lesson learned). I am considering to just invest on something off auber or an RTD off amazon.

I was reading ~145* at garage temperature
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