Question: I have an analog motor controller that has a B10K potentiometer on it. I'd like to be able to swap out the analog potentiometer for a digital one, but I'm not exactly sure what voltage is being sent to the original potentiometer as I don't have the spec sheets for it.

My current specifications, which work as a prototype, are:

```
- Power supply: 48V 4A transformer, connected to...
- Variable speed DC PWM Motor Controller which controls...
- A 130V 1A max DC motor. 

```

I'm fine with the power and speed that 48V gives me, but do I need to specifically look for a digital potentiometer that can handle high voltages, or would a standard 10K digital pot work?

Answer: 
![schematic](https://i.stack.imgur.com/osUds.png)

[simulate this circuit](/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fosUds.png) – Schematic created using [CircuitLab](https://www.circuitlab.com/)

*Figure 1. (a) 2-wire 4 - 20 mA sensor and (b) 3-wire sensor configurations.*

One way out of the problem - but perhaps not easily achievable with the XTR115 chip - is to add a third wire. You now have a greatly increased power budget.

[![enter image description here](https://i.stack.imgur.com/AVeBc.gif)](https://i.stack.imgur.com/AVeBc.gif)

*Figure 2. Different arrangements for 2-wire and 3-wire transmitters. Source: [e2e.ti.com](https://e2e.ti.com/support/amplifiers/etc_amplifiers__other_linear/f/18/t/263177).*

2-wire 4-20mA Transmitter:

* Accepts loop-supply from 4-20mA receiver
* Sinks a return current between 4-20mA

3-wire 4-20mA Transmitter:

* Accepts power and GND from a local supply
* Sources an output current between 4-20mA

For the 3-wire transmitter you may be better using the [XTR111](http://www.ti.com/product/XTR111/technicaldocuments).

[![enter image description here](https://i.stack.imgur.com/EKiF7.png)](https://i.stack.imgur.com/EKiF7.png)

*Figure 3: XTR111 application note extract.*
You have a few options but it depends on how much current you require and how much burden voltage you can tolerate.

The obvious solution is to use a small DC-DC converter to step the incoming voltage down to a lower value. This will give you more current at the expense of increasing the minimum burden voltage.

Please modify your question stating exactly what your requirements are.