SLC 500 RTD Module readings


Thread Starter

Brian Seal

I am using a AB SLC5\04 processor with a 1746-NR4
RTD module and a omron 100 ohm platinum RTD.
The channel is configured for engineering units, degrees Celsius and a excitation current of 2mA.
It is giving a reading of about 60 when it should be about 5.
any ideas?
_IF_ I remember correctly the SLC module is not a 4-wire measuring device. When reading an RTD you are just using a fancy ohmmeter, ie forcing a known current thru the device and measuring the voltage drop. Since the RTD changes very little w/ tempr, it sounds like you may be measuring the voltage drop in the connecting cable. Check that all connections are VERY solid (no splices allowed) and that the distance is not more than a few tens of feet. One way to check things is determine if tempr CHANGES are about right. If so, then it's probably the cabling. If not, then you may have a ground loop or may be exceeding the voltage-to-ground rating of the SLC module.