I'm working with an IDEC FC5A PLC that has an Analog input module (FC4A-J2A1). I'm running an ultrasonic level sensor to this input. I have checked the calibration of the sensor and verified its output is correct with a fairly accurate Fluke 87v. The input is set to scale 4-20 mA to a value of 0-84 and store that in a register.

If I have a value of 12mA for instance this should give me stored value 42, shouldn't it? I'm getting about half of that. So, I doubled the scale to be 0-168. That was much closer but still a bit low. I again changed the scale to 0-180 and now this seems to be pretty close.

I'm wondering if the IDEC Analog input module is just not reading accurately. I can't see what mA value it is reading. I can only see the scaled output value. Is there somewhere I can see the mA value the input is seeing?

If the module is just not accurate is there a calibration I can do?

Thank you.

 

Is the ultrasonic level sensor loop powered or externally powered? If the level sensor is externally powered, can you program it's 4-20mA output to be passively powered? What parameters do you have set up in the PLC card Configure Parameters dialog box?

 

1. Have you tried connecting multimeter in series with the transmitter and compared the value in the HMI or ladder program?

2. Have you tried simulating the transmitter while the multimeter is connected?

3. Have you checked all your parameters that everything is configured as 4-20mA and not something else?

4. How much voltage you are getting in the input channel?

5. Both scales (transmitter and program) are the same? I mean, your transmitter is scaled as 0-84 engineering units like your program as 0-84 engineering units? They should be the same.

 

Is the ultrasonic level sensor loop powered or externally powered? If the level sensor is externally powered, can you program it's 4-20mA output to be passively powered? What parameters do you have set up in the PLC card Configure Parameters dialog box?

The sensor is loop powered. I have very limited configuration for this in the PLC as seen in this image. I am on CH0 and I originally had this set to (Min = 0, Max = 84) but again that was way off. I reason for 84 is that I want it scaled to inches with the max being 7 feet. Because it was off, I had to set the max to 180 to get close, a bit of a poor man's calibration.

1. Have you tried connecting multimeter in series with the transmitter and compared the value in the HMI or ladder program?

2. Have you tried simulating the transmitter while the multimeter is connected?

3. Have you checked all your parameters that everything is configured as 4-20mA and not something else?

4. How much voltage you are getting in the input channel?

5. Both scales (transmitter and program) are the same? I mean, your transmitter is scaled as 0-84 engineering units like your program as 0-84 engineering units? They should be the same.

Yes, as mentioned I have confirmed that the output of the sensor in mA is accurate at the PLC. I did this with a Fluke 87v. I don't have a way to simulate the transmitter to the PLC input. As seen in the image above, I do have the signal set to 4-20 mA. On point 5 yest the transmitter is working great. Again, I have verified that the output of the transmitter to the PLC at the PLC is very accurate by measuring at the sensor with a tape measure the distance to the fluid and them over at the PLC i have my multimeter inline measuring the current. The current output to the PLC is correct for the fluid level. It just seems to me that the PLC is not accurate in its measurement of the current it sees at the input and is thus showing me an incorrect value. I can't verify what the PLC sees exactly as I only get to see the scaled value. On point 4 I have not measured it at the PLC but it's a 24v loop and it was right at 24v at the sensor, just a tad below, so I imagine it's not far off at the PLC. However, that's why we use 4-20 mA as not to deal with voltage drop on a 1-10v sensor.

 

Try different configurations in the PLC so you can do some more diagnosis, try Binary Data, 4mA should equal 0 and 20mA should equal 4095.

 

I don't have an IDEC I/O module or any software for it. But looks to me that something is wrong in the configuration. Try to explore and you might find something that is not appropriate. Check for codes in the diagnostics appearing when running online.

 

The analog input card turned out to be bad on ch0. Replaced the card and that issue went away.

 

Then that should be seen in the diagnostics. Thanks for the update..