using a 4-20mA sensor with a FP-AI-C420

[Paul in STL]

Just got a FP-1601 with a FP-TB-10 and a FP-AI-C420. Want to use an Omega 0-30 HG" sensor that outputs a 4-20mA signal. Connected the +24 to the sensor and output from sensor to 1a terminal. Then connected the 1b terminal to 24 Common. Getting no signal (out of range). Meassured the voltage drops accross sensor at about 3 VDC and with about 21 accross 1a to 1b. This appears to be an indication that the impedance of the AI module it to high. All documents shows that the impedance should be 133 ohms. I then took a current reading of the loop and I am showing about .06mA. Using ohms law, I get about 355K ohms impedance of the AI module. What gives? Anyone can lend me a hand with this problem? TIA Paul

[tst]

hellow Paul
I use FP-AI-C420, and measure 147 ohms accross 1a to 1b. May your FP-AI-C420 is not inserted correctly, or you have a bad one.
Try insert it again until it klicks to both sides, or replac it.
Helps ?
Shimon

[Paul N STL]

tst, Thanks. I was getting to the point where I could see the tree. But could not see the forset any more. I took my ohm meter and checked right on the 1a and 1b terminals. Low and behold I had 400K ohms. So checked 2a and 2b and it was as you stated about 130 ohms. Have second module installed as both read 130 ohms. Swapped modules and still the first 1a and 1b terminals where at 400K ohms. Offset the modules to the 2nd and 3rd openings and all is well. So looks like the TB-10 has a bad slot in the first location from the left.

Thanks for giving me something to think about and check out.

[JaredA]

Hello Paul,

It does indeed sound like you have a bad slot in your TB-10. But there is one more thing that you should make sure. With the TB-10 and dual channel modules it is very important to ensure both sides of the dual channel module get pushed in all of the way. Sometimes you can even hear the two clicks and the module not be seated all of the way. At the discussion thread linked here, you can find a picture showing what the Dual Channel modules should NOT look like when connected up to the TB-10. If this doesn't seem to be an issue for you, then it's most likely a d
amaged slot as you suggested.

Jared A

[Paul in STL]

Hi Jared, thanks for the addictional information. But this is not my problem. I did notice that the modules do take a bit more attention while FULLY seating them into the TB-10. With 400K ohms across the 1a to 1b terminals, it appears that there might be a cold soldier joint either at the screw terminals or the socket that the module plugs into.

Thanks for the suggestion.

Paul