Reading a Keyence FT-50AWP temperature sensor with NI-9208

[Dave_Thomson]

I'm trying to interface a Keyence FT-50AW to LabVIEW by reading its 4-20mA output with a 9208 on a cRIO. The Keyence manual shows that the output is a current source. E.g. you could drop the current over a reference resistor and measure it with an analog input module. But the current input module was already purchased, so I'd like to make this work. The Keyence schematic is attached below. The NI 9208 manual (screen shot also below) shows how to connect a 3 wire sensor. Since the Keyence has power and ground wires explicitly, this is the most obvious of the two possible connection choices.

However, I get no signal. The signal looks like its near ground, just bouncing around a little in the e-7 range.

Is it possible that the NI 9208 in three wire mode is not compatible with the FT-50AW?

[Dave_Thomson]

I posted the wrong schematic. Here is the device we're using.

[Sekine108]

You mentioned that this is a current output and that you'll be dropping this over a resistor? What value of resistor are you using? Are you doing any strange configuration with that resistor?

[Dave_Thomson]

I was only suggesting the resistor in an attempt to understand how the NI hardware works.

In any case, it is working now. The documentation was a bit lacking. There are six leads: Power, Ground, and four signal wires. Two of the four wires can be used as digital outputs. Two can be used as digital inputs. And two can be used as analog (current) outputs. But the documentation doesn't say which two of those three functions share wires. I assumed it was the digital wires. You would change them between being inputs and outputs. But no, it's the digital input wires that can be changed to be analog outputs! So I was just on the wrong wire!