XTR111: XTR111 and XTR117

Purushottam Pawar

Part Number: XTR111
Other Parts Discussed in Thread: XTR117, XTR300

Hi,

Greetings!!

We are using XTR111 and XTR117 in 3 wire transmitter and loop power transmitter (2 wire).

As I understand 3 wire transmitters are working in current source configuration and loop power (2 wire) transmitter working in current sink configuration.

We are using PWM of microcontroller for generation required input voltage for both XTR111 and XTR 117. Please note we have 2 separate transmitters where we have used XTR111 and XTR117.

Now we would like to combine both current sink and current source in a single transmitter but at a time only one configuration is selected.

What is the possibility of implementing this or any other suggestions.

Regards,

Purushottam

9 months ago

+1 Clemens Ladisch 9 months ago

Guru 283290 points

XTR117 is not a sink; it can be placed anywhere in the loop. And it expects to be powered from the loop; how are you going to combine them? How is that single transmitter supplied?

0 Purushottam Pawar 9 months ago in reply to Clemens Ladisch

Prodigy 60 points

Hi Clemens

The transmitter is supplied with 24V.

As of now we have 2 seperate transmitter, one with XTR 111 (3 wire -24V,GND and 4-20mA) and another with XTR 117 (2 wire - 24V and 4-20mA over GND)

But there are some transmitters available which says both current source and sink option is available in one transmitter (with some hardware or software selection)

I am not sure how this can be done.. I have found XTR300 which application note says both sink and source is possible with it. But it requires bidirectional supplies..

In one of the thread on this forum it is suggested to use discrete op amp based design.

Is there any application note available on current sink and source with single ended supply 24V and GND.

Regards,

Purushottam

0 Clemens Ladisch 9 months ago in reply to Purushottam Pawar

Guru 283290 points

The XTR117 can be put anywhere in the loop, so you can use it like a sink.

But it is not possible to use two transmitters in the same loop, because each one would try to limit the loop current to its own value. You would need some kind of switch to disable one. How could this be done? Is there a control signal?

+1 Purushottam Pawar 9 months ago in reply to Clemens Ladisch

Prodigy 60 points

Yes..I agree that both XTR111 and XTR117 can not be used together.

We will have a selection switch,when it is to be used in source mode the voltage signal from MCU is applied to XTR111 and when it is to be used in sink mode,the same voltage signal is removed from XTR111 and will be applied to XTR117 .

e2e.ti.com/.../xtr111-2-wire-and-3-wire-current-transmitters-in-the-same-circuit-xtr111-and-xtr117

Will this logic work..

Thanks,

Purushottam

0 Clemens Ladisch 9 months ago in reply to Purushottam Pawar

Guru 283290 points

Switching the input voltages will work. But you still have the XTR117 ground problem mentioned in the linked answer; the IRET pin must be allowed to float (it wants to be a little bit above the negative loop terminal).

0 Luis Chioye 9 months ago in reply to Clemens Ladisch

TI__Guru 54556 points

HI Purushottam,

As Clemens has mentioned, on a 2-wire current transmitter, the IRET or local GND of the 2-wire current transmitter, needs to float with respect to the loop ground. The IRET (local ground) potential moves as a function of the current loop load resistance, and the output current of the transmitter. For every instance of a 2wire transmitter, the IRET must float independently according to the output current. On each 2-wire current transmitter, all the circuitry that drives the 2-wire current transmitter needs to referred to the specific floating IRET and not to the loop GND.

Below is a blog series on 2-wire current transmitters that you will find helpful.

2-Wire 4-20 mA Sensor Transmitters: Background and Compliance Voltage (Part 1)

2-Wire 4-20 mA Sensor Transmitters: Understanding the 2-wire Transmitter GND (Part 2)

On the 3-wire current transmitter, the ground is fixed and normally referred to the same loop ground.

Another important factor to consider on the 2-wire transmitter is the total current consumption. The total current consumption of the 2-wire current transmitter module, including the XTR117 and the driver circuitry (including the DAC ) must not exceed 4mA. In some cases this can be a limiting factor when using a microcontroller-DAC to drive the 2-wire current transmitter. Below is a blog providing a detailed discussion/explanation on the 2-wire current transmitter current consumption limitations and suggested solutions:

2-Wire 4-20mA Sensor Transmitters: Sensor and Transmitter Current Consumption Limitations (Part 3)

2-wire 4-20mA transmitters: Controlling 2-Wire Transmitter Outputs with Externally Powered Sources (Part 4)

2-wire 4-20mA sensor transmitters: Designing Input Isolated 2-Wire Sensor Transmitters (Part 5)

Because of the grounding differences, you may not be able to combine the 3-wire and 2-wire transmitter sharing the same ground potential or the same DAC circuit simultaneously as you have drawn on the diagram above, unless the ground connections, and driver devices are re-configured for each case. You will also need to be careful of the total current consumption on the 2-wire current transmitter.

Thank you and Regards,

Luis

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XTR111: XTR111 and XTR117