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Author Topic: RTD Signal Conditioner  (Read 1556 times)

Offline hoptomation

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  • Posts: 18
  • NW Minnesota
RTD Signal Conditioner
« on: July 21, 2010, 03:24:57 pm »
I was wondering if anyone had some first hand experience with a RTD signal conditioner that they could recommend.  I am looking at doing some equipment automation utilizing a PLC and would like to land the RTD on a 4-20mA analog input rather than buy a separate RTD input card.

I can find plenty of signal conditioners to choose from but am looking for something more in the typical homebrewer's price range ;) ,  similar to the pricing of the automation gear that can be found at
Cheers - Luke

Offline abraxas

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Re: RTD Signal Conditioner
« Reply #1 on: July 21, 2010, 04:42:48 pm »
There isn't much in the hobby market for a RTD signal conditioner that I've ever come across.  I'd look for a used temperature controller with an auxiliary output, something most of the cheaper Chinese ones don't seem to have. 

Thanks for a new site though, might have to dig through it later tonight and see if there are any goodies. 

Offline dhacker

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Re: RTD Signal Conditioner
« Reply #2 on: July 21, 2010, 04:54:31 pm »
I haven't bought anything here yet, but the prices on PLCs and modules appear to be as good as I've seen.
Just brew it...

Offline wingnut

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  • Plainwell MI
Re: RTD Signal Conditioner
« Reply #3 on: August 02, 2010, 01:11:17 pm »

Building your own signal amplifier for an RTD is not very expensive, nor vary hard.  Essentially look up "Wheatstone Bridge" for the details, but 2-9V batteries and 50cents of resistors can create what you need.

The abstract is, an RTD is just a fancy resistor that changes resistive value based on temperature.  Using a voltage source, and three other known resistors (choosing the resistance value takes bit of thought), a proportional voltage change can be sensed on the RTD.  Based on how the resistors are selected, the sensitivity of the system can be changed. 

I set up something similar using a load cell (resistance varies with weight), so that I can measure how much water is in my kettle, and track boil off rates or monitor sparge water rates. 

I am just guessing, but if it is a 1kohm RTD, then you would put the two 9v batteries in series (giving you an 18V DC power source) and choose three 1kOhm resistors  for the other devices.   If your RTD was scaled 0-1000Ohms equals 0-300F then you are looking at a sensitivity of about .0165V/deg F.  By choosing a more sensitive RTD or varying the resistors, that can make things more sensitive.

Good luck!
-- Wingnut - Cheers!