Sensor compatibility 1-Channel 4-20mA current loop receiver

Hardware
1

I am seeing an issue with the module reporting 4mA and 0mA. I have 3 devices in the field.

One has been working fine, one has been intermittent, and the 3rd has been stuck at 4 or 0 mA.

Has anyone seen this before?

I am questioning the load resistance.

Using 16V gives me 181 Ohms in the equation below…

Let me know if there are any questions.

Here are the power supply specs from the sensor manufacturer.
Operating voltage 11.6 … 35 V DC

Reverse voltage protection Integrated

Permissible residual ripple

  • for 12 V < UN < 14 V ≤ 0.7 Veff (16 … 400 Hz)
  • for 18 V < UN < 35 V ≤ 1 Veff (16 … 400 Hz)

Load resistor

  • Calculation (UB - Umin)/0.022 A
  • Example - Non-Ex instrument with UB= 24 V DC
    (24 V - 12 V)/0.022 A = 545 Ω
2

Hi Mike,
It looks like an under power situation.
I believe it works fine if you are using with 2 devices ?

Thanks

3

@Bhaskar

As always thanks for the quick response!

I am not sure if I follow you though.
The voltage range of the sensor is 12-35 VDC.
It is a 2-wire loop powered unit.

Here is the sensor I am using.

Do you see any problems with the sensor?

4

sorry … i thought you are using 3 channel board. In your setup you have a one channel 4-20mA current loop and one level sensor ?

can you use a meter to read the current change ?

are you connecting the shielding wire to ground ?

5

Correct There is a one channel current loop receiver PR33-7 connected to one sensor.

I can try to measure asap the one that is at my office is one of the intermittent ones and is currently reading ok. Would you still like me to measure the current?

I have been leaving the shield disconnected.

6

if you dont mind sharing can you share the output log of the one which sometime works sometime doesn’t ?

I think it will be good idea to measure the current using a meter and keep a log of it for analysis.
I would like to see if the meter reads correct when the board doesnt

7

I will try to gather that data asap!

Would tying the shield to ground help?

8

I will recommend shielding. it will help in noise reduction.

9

What might cause the voltage booster to output less than 16V DC?

Here is the past week of readings. 26.7 = ~4mA & 0 = ~20mA.

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Today I cycled power to the mcu, level shifter and loop reciever and it started reading correctly but I believe there were ~ 12V DC across the terminals. Before I cycled power there was a little over 8V DC.

  • I am not using your i2c level shifter…
10

How are you powering up the 4-20mA input board ?

generally voltage could go down if too much power pulled from the power supply.