T3-TB 4-20 input issues

Troubleshooting
1

Hi there,

I have been using some 4-20mA pressure transducers for quite a while on the T3E-886’s without issue.
I have swapped one of the T3E-886’s out for a T3-TB however the input isn’t reading right. The value when checked via a multimeter is 8.58mA, however when connected to the T3-TB the output is reading around 3.46mA occasionally peaking up to around 8.58mA where it should be. The LED on the input is also flickering from bright to dull sporadically.

The wiring configuration is as follows:
24v PSU (+) —> Transducer (+), T3-TB (+)
24v PSU (-) —> T3-TB (-)
Transducer (-) —> T3-TB (Input 1, top row).

Any help is appreciated, cheers.

Edit: I thought I would note, I have tested with two other types of pressure transducers, and one of those types worked fine. And for the moment I have put a 500ohm resistor across the input, and am reading it in as 0-10v which will get me out of trouble.

1 Like
2

Good troubleshooting there BG. The T3 controller uses a multiplexed input scheme to share several inputs with the A/D hardware. The 20ma current is dropped over a resistor on board our controller to generate the 0-3V signal which the A/D converter sees. The fact this resistor is muxed means that your transducer will only see current flowing for a few milliseconds each scan. Depending on your transducer it may take a while to settle down its output signal. It has taken your good troubleshooting to call us out on this, thanks for that.

I am guessing on the TB the signal must go straight in with no mux.

We managed to fix this on our own transducers by tweaking the firmware on the sensor side but in your case this is probably not an option. Which sensor are you using? We could possibly fix this with a firmware update on the T3 controllers.

1 Like
3

Thanks for the update.
Below are a list of the sensors used in testing.

Submersible Sensor - Not Working

Screw in type - Not Working

Submersible Sensor - Works

1 Like
4

We’ll round up some samples and test them out. Thanks again for the good troubleshooting there.

Update: I dropped the ball, we will get some samples here and report back shortly.

1 Like
5

I use myself the same kind of sensor, but 0-10V with a T3-TB since more than a year, without any flaw

Why did you choose 4-20mA instead of 0-10V (genuine question) ?

Submersible Sensor

image
image882×433 111 KB

6

Good point, the 0-10V range will work even with the muxed arrangement of our A/D hardware. It’s the 4-20ma current signal which will have trouble with the muxing because of the quickly varying impedance of the mux. I asked our team to round up a few samples of both the 20ma and 10V type, this is a good sensor for tank monitoring which I have been meaning to add to our lineup.

1 Like