4-20 mA sensor read

Hi

I have made a setup like this to read the milliamps from my 4-20 mA pressure transducer. Do you think it will work or I will gonna be in trouble? (I am not very good with electronics, I just passed some course in highschool 15 years ago :slight_smile:

Best regards

Zeedo

IMG_1404.JPG

First please provide a link to your pressure transducer. Without that, it's a shot in the dark.

Hi Power_Broker

It is this item:

the specific model number is : 692902007141 which gives this spec:

0 ... 0.2 bar max. 1.2 bar Sealing material FPM Fluoro elastomer Adjustment Factory

Important: Output / power supply 4 ... 20 mA 11 ... 33 VDC

Connector 3) DIN EN 175301-803-A

Screw fitting CuZn nickel plated for pipe outside ± 6 mm

Looks good to me. Have fun and good luck!

Have a look at the rugged Arduino or industrino web sites - they show over voltage protection circuitry to protect analog inputs against faults , you might want to consider that.

You would usually put the sense resistor on the other side of the sensor, so the Arduino ground is connected to the 24V ground. The sensor ground is then always within 5V of the ‘real’ ground.

There’s no protection in this circuit if the 24V supply is connected backwards or connected to 110V. Depending on where you are using this and the skillful inventiveness of the people using it, you should consider adding more protection.

Thank you all for your great answers,

Yap, it is better if I put the resistor after the transducer.

What can be used for protection? A diode? A fuse?

The MAX14626 is a good protection chip, if you feel you need that level of protection. Like I said, it depends on the inventiveness of the users. Often that's just me and then I do need to protect against stupid things.

Hey Guys sorry to dig up an old thread but i hope someone can help me, I have an application that i need to measure 4-20ma signal from a transducer but the difference is that the current loop is switched on and off with a photofet. im not sure how to wire the device since the arduino and actual current loop is powered of the same battery.

Attached is a wiring diagram

What's connected to pins 1 & 2?

the positive and negative of the sensor.

That looks bad. Consider what happens when the photoFET is off. There is no current flowing through the sensor and the sense resistors. But one end of that is connected to 12V. With zero current, there is zero voltage drop so everything is now at 12V, including your Arduino pin A0. That will destroy the Arduino.

Put the photoFET in the 12V line, before pin 1 of the sensor.

Also consider what might happen if the sensor wires get accidentally slammed in a door or cut with big pliers. That will put 12V directly onto your sense resistor R12. How much current will flow? Is that within the power rating of that resistor? How much current will flow to the Arduino 5V pin when the other end of R16 is at 12V? Is that current small enough that the protection diodes on the Arduino will survive? You want to keep this fault current from 12V to 5V around 1-2mA.

Rustie0125 already had an answer here.

Leo..