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Hi everybody!

I'm trying to configure a 4-20mA current loop to read the output of a sensor but I keep receiving constant values. The sensor should be working, so I guess the problem comes from the configuration I'm using:

where R=250 ohms resistor. The blue+ cable goes to pin #9 whereas the black- goes to #6, as suggested in the documentation: https://wiki.teltonika.lt/view/Current_measurement_with_RUT955_analog_input

What am I missing? Any tips are welcome :) Thank you very much in advance!


Hey, sorry for the necro thread but I was looking for info to jog my memory on 4-20mA into RUT955 and found this post. I wanted to let you know if you hadn't figured it out two things I've found. I think both issues depend on the firmware version on the RUT. If you're still playing with this: 

  1. I've seen behaviour where in the GUI nothing displayed (0 / no value) for the analog input unless you have an input rule created for current/voltage.
  2. Most recently (different firmware) I'm seeing 0 / no value in the GUI at all but using the CLI like cat /sys/class/hwmon/hwmon0/device/in0_input as described here will show fluctuating values in millivolts. There used to be an older command listed in the wiki there that became obsolete at some firmware but looks like the page has been updated with correct info.

Current FW RUT9XX_R_00.06.07.7

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Hello. As I can see you are trying to power up the Sensor via tha same current output line of the sensor.

Maybe the Specific model of sensor is designed to work in that way (Maybe not). But in any case, the example we published in the page is for a sensor with power lines separated from Current Output lines.

Can you post the specific model and brand of sensor you are using?
Best answer

Hi there! 

The sensor is a radar for water level measurement: https://www.vega.com/en/products/product-catalog/level/radar/vegapuls-wl-61

I have seen several similar setups on the internet, like this one:

but I guess I'm missing something.



Even tho that the debug of the Radar sensor is beyond our scope, I can make a few comments.

in page 26 of the Operational document I can see that the device performs a series of steps before sending any measurements to the curre


Also the 250 ohm resistor is set for a 0-5 Volts input and this input can go to up to 30V. This is just for you to keep in mind when you make the corresponding calibration.

To debug the RUT955 device you should feed the input with 2 or 3 different voltages (for example 5, 12, 24V) and see if there is variation. (It will be better if you have a variable output powersupply so you can see the variation)

Also you will need to supply the resistor values you are using for the circuit, in order for the interface to output the right current values according to the Voltage Input



Remember that the device checks the analog voltage every 3 seconds by default.