Connecting 24v and 3.3v sensors to Particle Boron

[boron]

I am looking to monitor surface and water temperatures using a Particle Boron, Type E thermocouple wire + Adafruit MAX31856 (3.3v), and a 24vDC 4-20mA infrared sensor.

1. Is it possible to use the 24v sensor powered externally, grounded with resistors to the Boron? Will the 0-3.3v be compatible?

2. If it is possible, can the two sensors be used simultaneously? I know there is only one ground, so I am thinking that the two would need to share a ground.

3. There are also IR sensors that output via Type K thermocouple. Using one of those, the 24v sensor would be entirely ignorant of the Boron’s existence. Just have two thermocouple amplifiers, one reading the Type K output from the sensor and the other reading normal thermocouple water temp.

I have attached a crude wiring diagram. I am certain something here is wrong, any ideas are greatly appreciated. Thanks!

[peekay123]

@boron, yes, you will need a common ground. However, the 4-20ma sensor produces current, and I see you have a “low side” (after the sensor) resistor on your diagram. Typically, the resistor is on the high side with the sensor returning to GND. As you have it, there is little protection from over-current or over-voltage at the Boron ADC inputs, which is only 3.3v tolerant. You may want to look at the Particle Tracker 4-20ma interface app notes for inspiration. In your case, the 24v supply would be external from what I understand.

Tracker 4-20mA sensor | Hardware