1769-IR6/A RTD reading

Hello all,

I am fairly new to the PLC world and doing some self learning to pick up the nuances. Your help is highly appreciated.

Question: I have a 1769-IR6/A RTD module in the field and have my configuration sensor type set to 100 ohm pt 385 type. When I connect a 20 ohm direct resistance across SENSE and RTD (EXC and SENSE are shorted), I get a value of -1950 on my ChData.
Is this value my temperature ? If so, what is the formula behind it ? I know this sensor type would read 0C at 100 ohms.

Many Thanks !

What you are seeing is probaly the Raw Analog Value and you will need to scale this to your temp range.
Much the same way you would need to scale a regular analog input.

It will depend on how you have your module configured as to how you will scale this.

Page 50 - 53 of the attached document describes configuring the module.

Page 54 shows you the Data Formats.

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1769-um005_-en-p.pdf

BCS

Hello Bering, thanks for the prompt response ! I had already looked at that document and the pages you suggested. Below are the details of my configuration file:
Data Format - Engineering Unit X1
Sensor Type - 100 ohm Pt 385
Units - C
Open Circuit Response - Upscale
Excitation Current - 1.0 mA
Filter - 60 Hz

Could you now tell me what that value -1950 means ? I am still unable to figure out the math.

Thanks !

20 ohms would be about -197 deg C.

Your read is with an implied decimal point of one place.

See pdf below.


http://www.omega.com/temperature/Z/pdf/z252-254.pdf