4 channel 4-20 mA Transmitter problem

Hardware
1

Hi,

I am trying to use your 4 channel 4-20 mA Transmitter and I observe this behavior:

  • When I connect a single channel (any of 4 1-4 channels) using a DC external supply + a load on CTO1, every thing works fine
  • When I am trying to connect/use a second channel using a second load but sharing the same DC supply on CTO2, I observe a major impact on CTO1 reading value!

I made test with several different supplies with same result
The only way where I got a good result was:

  • Using 2 different supply for CT01 and CTO2
  • Using to mA meter to observe the current

Do you have an idea of the problem?
Do you have a typical wiring example?

Thanks

Danny

2

Hi,
You cant use same power supply for multiple channels. the reason is this
lets say you connect a power supply to channel one and control the 4-20mA output, it will work fine. now lets say you use the same power supply with 2 channels and change the 4-20mA output of channel 2, it will also change the power supply current on channel one, because it will create a close loop for ch1 as well as ch2.

How many channels do you want to use with signal power supply ?

Thanks

3

We want to use 4 channels per supply

4

You can use 4 of these


with a I2C mux

this setup will let you use one power supply with all 4 channels.

Thanks

5

Hi Bhaskar,
I want to be sure that you understand my setup, as described in picture attachment, my supply is connected in parallel so I am not sure to understand why ch1 and ch2 are not totally independant even sharing same supply:

2018-04-02%2012_52_40-scanner_20180402_124946
2018-04-02 12_52_40-scanner_20180402_124946.jpg2528×1101 612 KB

Thanks
Danny

6

4-20mA_Forum
4-20mA_Forum.jpg2555×1122 189 KB

when loop one is active it will feed signal in the ch2 and this will cause false readings on the ch2.

7

4-20mA_Forum
4-20mA_Forum.jpg2567×1117 180 KB

You can try adding diodes and see if that separates the 2 loops. i never tried it but there is no harm in trying.

8

Hi Bhaskar,

I have tried diodes and solution doesn’t work
I bought 6 modules (4 channels) to do my job but it is not woking…

Is it possible to have some credit for the quad module since it is not usable and I gave to replace each of them with 4 single channel?

Thanks

9

please contact at orders@ncd.io.

(We are a custom manufacture and generally dont accept return of more then 5pcs of same board, but in this case we can workout something for you.)