6-ch temp control

UA-ChIEF

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Join Date
Nov 2013
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AZ
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1
All experts,

This is my first time to use PLC (EZPLC from EZAUTOMATION.NET) to make a 6-ch temp controller using pt1000 RTD. The RTD I/O module I bought from them does not work (admitted by exautomation.net). I use a current source going thru the pt1000 to generate a voltage. Then I use the anolog voltage input I/O module to input to the PLC box. The goal is to use the temp sensor to control a heater and a LN2 (liquid nitrogen) solenoid switch to regulate the chamber temperature. However, I never worked on PLC before. Please advise how to start this and any example program (of any application) would be very helpful to me to get it started. Any your expert comments would be very much appreciated. Thanks a million in advance.
 
I am not familiar with EZPLCs so can't help with programming.

I would be vary careful with applying a current to your RTD as typical excitation currents from RTD modules are in the .25ma to 1.0ma range.RTDs are not very big ( wiring size). With that amount of current you are not going to get lot of voltage. Poor resolution. Also your response is not going to be linear without a RTD module.
 
Last edited:
the excitation of a Pt1000 is max 0.1 milliAmp giving 100 millivolt is 0.1 Volt
as the span of a Voltage input is 10 volt you will not see anything moving maybe 1 digit.
You will need a specialized input (i looked at the specs of their RTD input, and yes the text suggests it has Pt1000 but i think it only has Pt100 Ni100 and lower like Cu10 etc.
the excitation is 0.5 milliAmp, way too much for a Pt1000
some workarounds:
1. connect a 100 ohm resistor in parallel and check if it is working (not correct but it will give some input.
now take a ice box and check the value and do same in a hotwater boiler (to make tea and just hang the Pt1000 in.
you will get values however the resolution is only 1 degree instead of 0.1.
2.find yourself Pt100 sensors they do work.
3. get 10x Pt1000 and put them all parallel this way you have a correct input.
4. use a converter IC to translate from Pt1000 to 4/20 mA like the XTR102.
 

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