4-20ma to deg F

DCCCOLE said:

I have a type j thermocouple going into a 4-20mA transmitter. That is connected to and Allen Bradley 1762-IF8. The transmitter has a span of 0-300 deg F. How do I covert the 4-20mA signal into a deg F. in RS Logix 5000.

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I would use a CPT instruction. Take your input signal 4-20mA and divide that by the 20mA signal (32640) and then multiply that value by 300 (your high temp). This should give your reading.

Here's an example:

CPT

Compute
Dest Temp_Tag (Tag containing your temp)

Expression (Local...whatever point your device is)/(32640)*300

So...lets assume your local input point is giving us a reading of (16000). Take this reading and divide it by (32640 which equals 20mA which equals 300F). This gives you (0.49) or 49%. We take this 0.49 and multiply this by 300 which gives us 147F. The 147 vallue will show up in whatever tag you create in the Destination which I named "Temp_Tag".

I hope I explained this clearly.

This is how I scale my analog signals.

Good luck!

You need to determine how your AI card is configured. Sometimes the live zero (4 mA) is maintained by the data register, so that instead of 0-32000 as 0-300 F at 4-20 mA, for example, you may have a data range of 6400 to 32000 In that case, the 4 mA signal at 0 F will show up as 6400 in your AI register instead of 0 in the data register.

Tom Jenkins said:

You need to determine how your AI card is configured. Sometimes the live zero (4 mA) is maintained by the data register, so that instead of 0-32000 as 0-300 F at 4-20 mA, for example, you may have a data range of 6400 to 32000 In that case, the 4 mA signal at 0 F will show up as 6400 in your AI register instead of 0 in the data register.

Click to expand...

Good point

I was refering to 1769 analog cards. Just check out the PDF file for your particular module.

Hey DCCCOLE

Is the module a 1762 or 1769? I do not see a 1762-IF8 module on the rockwell site. I do see 1762-IF4 though. Just curious. The 1762 is a micrologix platform.

kandymann
Sorry it is a 1769-If8
I used our formula and got it to work.
thank you