Solution for 4-20 mA control of 7 devices using Arduino?

Hi all,

I am currently preparing an industrial test setup where we will control 7 EC fans independently using 4-20 mA control signals. I would like to base the solution on using an Arduino as MCU, as this is what my experience is limited to.

I believe NCD provides a good solution for achieving this. However, I would appreciate if somebody could review my intended shopping list below and evaluate if this would be suitable for me to achieve the intended control.

Proposed items:
2 x PR33-27 - Isolated AD5696 4-Channel 4-20mA 16-Bit Current Loop Transmitter with IoT Interface
(2 x PR37-3 - I2C to IoT Interface Adapter - included in PR33-27 as far as I understand)
(2 x PRacc-1 - I2C Cable for nodeLynk Devices and Sensors - included in PR33-27 I understand)

I do not expect an Arduino IoT Interface Adapter is strictly necessary as I would just intend on connecting the Arduino using one of the I2C nodeLynk cables (PRacc-1). Is this understanding correct?

Otherwise, my main concern is whether the two 4-channel transmitters can be connected directly in a nodeLynk loop or if an I2C multiplexer is required?

I hope somebody will be able to support me as my knowledge on the topic is basic to say the least.

Finally, thank you for taking the time to read my post and have a nice day!

With best regards,
Rasmus

Hi Rasmus,
Your setup looks great.
you can daisy chain two PR33-27 no need of any i2c mux.

Thanks

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Thanks for the support, Bhaskar. I am happy to read that!

A few follow-up questions regarding the 4-channel transmitter:

  1. “The On-board XTR1115 4-20mA Current Loop Transmitter has a wide Loop supply range from 7.5V to 36V”.
  • Looking at the wiring diagram, I see two options for 12 V input. I suppose these inputs then support a 7.5-36 V range. Is that understood correctly?
  1. “Separate and Independently Isolated Power Supply Required for Each Output Pair.”
  • Can you comment on this? I suppose there is only a single power input on the PR33-27 (the 12 V input mentioned above). What is the risk of using the same input power supply for both PR33-27s?
  1. correct. that’s the range of loop supply.
  2. correct. we use 12V as example
  3. you can use same supply to power both boards, but will need a unique supply ofr each loop.

If you want to use only one power supply for all then you will need

  1. 1pc
    https://store.ncd.io/product/pca9547-8-channel-i2c-bus-multiplexer-with-reset-with-i2c-interface/
  2. 7 pc
    https://store.ncd.io/product/1-channel-4-20ma-current-loop-transmitter-i2c-mini-module/

This will let you use one supply to power everything.

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Thanks again, Bhaskhar! I really appreciate your guidance.

I am sorry, but I am still a bit confused regarding Point 3. I have indicated to board and loop power supplies as I understand it on the wiring diagram at the bottom of this reply.

If this is correct, then I would expect the board to function as follows:

The 4-20 mA output channels do not function as a current source, but instead control the loop impedance to achieve a 4-20 mA current draw from the loop power supply.

Is this correct?

Finally, just to understand, what could go wrong using a single power source for all boards and loops?

like your wiring diagram you will need individual power supplies for each channel.
the transmitter board will control the current. if same power supply is used it will change on other channels as well.

Thank you, Bhaskar. I will submit an order shortly.

Just a few questions about the 8-channel I2C multiplexer as I prepare the code and circuit:

  1. Do the current loop transmitter mini modules automatically get assigned addresses in the range from 0x70-0x77 (of course depending on which port they are connected)? Or do I need to do something manually?
  2. What relevance does the start address have?
  3. On the multiplexer wiring diagram there are indicated 12 V board input voltage ports. Does it have to be 12 V or what board input voltage range is allowed?

Thanks again. Looking forward to receiving the parts!

  1. address will need be assigned in the software, checkout mux datasheet
  2. all device should have unique address
  3. the board can work form 9-24V.
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Thanks again Bhaskar.

Finally (for now), is there any Arduino sketch example available from you? Or can I use any sketches found in Arduino PCA9547 tutorials from other sources directly with your board?

you can use any code… its fairly straight forward code… basically it will be only one line of code.
You will define i2c address, reg location and what u want to write ( in this case it will be port number)

1 Like

Thanks. Hopefully this will be the last time I need to ask for support.

Hi again Bhaskar,

I just had a talk with a colleague who was sceptic of using the same power supply for multiple PR33-26 (passive) current transmitters.

He expected that an active transmitter such as the PR33-49 would be the correct mini module to be used instead for a single power source setup:

Could you clarify this?

I have received the PR33-26 transmitters but am hesitant to unpack them in case they are not compatible with single power supply use after all.

Thanks for your continued support.

PR33-26 can be used with single power supply.
PR33-49 eliminates need of a power supply because it has on board power supply.

1 ) So all seven PR33-26 loops can be the powered by the same supply simultaneously?
One loop will not affect the other loops if using the same supply? That is all I am trying to ensure.

EDIT:
2 ) It seems that the PR33-26 and PR-49’s difference to the 4-channel PR33-27 is the four channel digital isolator. Is this the reason that the same power source can be used for multiple PR33-26 loops?

EDIT 2:
3 ) The PR33-26 has an on-board R1SE isolated DC-DC converter, however it still requires external loop power supply according to the wiring diagram. Why is that? Does the on-board DC-DC converter not supply the loop current?

Yes you can use same external power supply for all.
Only pr33_49 will supply power to the loop . In this case you wont need power supply all together