4-20mA Pressure Transducer, 4-20mA voltage converter (?), and NodeMCU help?

ESPHome
1

I am struggling to understand how to make this 4-20mA 2-wire Liquid Level Transducer work with my NodeMCU. I had started working on this for-learning-purposes project at the start of this year but life got busy, and I’m only now able to dive back in.

Initially I tried not using the voltage converter, and just using a 150ohm resistor, but things didn’t seem to be working correctly. I purchased a 4-20mA current to voltage converter.

As I’m starting back into this project, I wanted to start back at where I left off. As of now, I am wired up without the voltage converter. When I measure across the power supply side I see 12.2v, when I measure across the sensor side I get 11.59v. This measurement is the same if the sensor is submerged in water or if it is out in open air.

I have tried searching for wiring diagrams and how-tos in order to get this set-up working, but I am just not having any luck and I am finding myself increasingly frustrated. I have zero formal education on this stuff and am just trying to learn a bit as I work on some projects that interest me around our home.

Do I need the voltage converter with my NodeMCU? Can anyone point me towards any documentation that might help? I’m sorry if this seems erratic, but that’s how it feels in my brain right now.

2

Photo and even possible link to where you bought it might get a response. There are many different types; unfortunately the ones I have are voltage ….

3

A precision 150R resistor should be all that is required, assuming you have no earth loops to other devices on the current loop. With that 4-20mA → 0.6-3.0V.

By precision I mean 0.1% or better tolerance, but really this is not important. The ESP ADC needs calibration anyway (it is quite non-linear at its extremes) so you could even get away with a 5% resistor as long as you use a calibrate linear filter.

4

This is the pressure transducer I purchased

5

It’s a current transducer, not a voltage transducer. Measure the output voltage with the 150R load resistor connected.

1 Like
6

@jcbennett There are some really good reviews on the link you posted on practical installation and wiring. Note carefully the atmospheric tube and how noisy the data can be. A good moving average or filter out movements less than a delta threshold.

1 Like