PR33-7 1 Channel 4-20ma, supply resistor getting hot-HELP

Here is the wiring diagram for the meter I am trying to use. Please note that it is a 24volt DC. So I have a resistor installed in the second picture attached. It calls for a 249 Ohm resistor but all I had was a 270 so I had to use that.

The problem I am having is when I plug in the PR33-7 the relay on my breadboard gets super hot, like fry an egg hot. Ugh.

I have the pull-up resistors in place on the PR33-7

Should I have bought the PR33-26 instead so I can eliminate the need for the resistor?

the board already comes with on board power and all other parts.
All you will need to do is plug the 2 wire sensor into the 4-20mA current loop board and it will power up the sensor as well as read it.

External power will damage the receiver.

PR33-26 is transmitter not receiver.

If you want to use an external power you will need to get this controller


Thats what I am trying to do. I have it wire just like the picture above shows. From “MA-” to “dislpay-” I am not trying to power the sensor. If I read the jumpers I am showing a voltage range of 1.08V - 5.4V going to the PR33. Now if I plug in the particle and measure voltage coming out of the PR33 it reads 12 volts.

  1. disconnect all the external wires from the 4-20mA board
  2. connect 4-20mA board to the particle i2c shield using an i2c cable
  3. power up the particle using a usb port
  4. the power led on the 4-20mA board should light up
  5. measure the voltage on the 2 screw terminals on the 4-20mA board ( it should be 16V)
    let me know what you find out

Correct, I show 16.6 volts on the fluke meter.

what the part number of the sensor you want to interface with this receiver ?


Its an air flow meter model 5200. it is not listed in any of the popular forums as it is used more in industrial settings. The image I posted was from them on how to wire to a 4-20ma data logger.

You can connect this sensor directly to the 4-20mA board. You wont need the 249Ohm resistor and external power. the 4-20mA board will take care of everything.


Thank you so much. Just to confirm that I can connect this sensor, that is powered by 24volts DC to the PR33-7 board. I want to make sure I don’t fry anything. Lol.

You dont need to power up the sensor using 24V, the 4-20mA will power the sensor.
feel free to post a picture of you setup/wiring before powering it up.


I wired like you said. I tried measuring the mA with the meter but the meter is showing 0 when put on the leads coming out of the flow meter, regardless of the flow change in the meter. It is also showing 0 in the particle console.

If I measure the voltage without the PR33 attached it measures 0.01, When I attach the PR33 I get 16.24 volts.

you will need to remove the wire jumper between mA+ and DC+. if you dont do that the flow meter will supply power to the 4-20mA Board and will damage the 4-20mA board.
connect the 4-20mA board wires between mA+ and mA-.


Thank you, I had removed it right after I took this picture. I am still not getting a reading. Is there a procedure for testing the board to confirm if it is still working and that I did not grenade it? :slight_smile:

Never mind the last question. I downloaded the mac serial tool and found my I2C channel was 0x49 instead of 0x48 which is listed in the ads1115.h file. The serial tool showed me that I did not blow up the amazing parts that I bought from your company. Thank you for all the help. Now I just need to figure out how to convert the mA readings into CFM. lol. You all are the best. Thank you again for helping this noob out. I really appreciate the support.