24V 4-20mA industrial temp sensor, how to connect/read?

[Grimmie]

Apologies, not sure where these “font” HTML codes came from, I didn’t put them there…

[Grimmie]

To be complete, this is the code I use:

/*

ReadAnalogVoltage

Reads an analog input on pin 0, converts it to voltage, and prints the result to the Serial Monitor.

Graphical representation is available using Serial Plotter (Tools > Serial Plotter menu).

Attach the center pin of a potentiometer to pin A0, and the outside pins to +5V and ground.

This example code is in the public domain.

http://www.arduino.cc/en/Tutorial/ReadAnalogVoltage

*/

// the setup routine runs once when you press reset:

void setup() {

// initialize serial communication at 9600 bits per second:

Serial.begin(9600);

}

// the loop routine runs over and over again forever:

void loop() {

// read the input on analog pin 0:

int sensorValue = analogRead(A0);

// print out the value you read:

Serial.println(sensorValue);

}

[Azkom]

Do you have an OpenPLC example for the same test environment?

[Grimmie]

Was hoping for at least some replies…

• This reply was modified 4 years ago by  Grimmie.

[Friedl]

Did you take into account (see datasheet of sensor):

Minimum Sensor Voltage
8 V DC (all other models)

Therefore you’d be better off if you’d be using a MAXI Automation (0-10V input) and a 500 Ohm resistor.

• This reply was modified 4 years ago by  Friedl. Reason: typo fixed

[Grimmie]

Hi Friedl,

Thank you for your reply.

I must admit that I did see minimum supply voltage @8v for the sensor. I ignored that for convenience sake. Because the readings did change with the temperature I asumed the sensor still worked, furthermore @100C the voltage would have been well over 8v, but the reading did not change significantly.

That being said, you might be right this is an issue. I do however not see how using the Maxi Automation in 0-10v with 500ohm resistor would help my situation, am I missing something?

The more I think about it I start to see this sensor simply isn’t suited for 4-20mA to 0-10v conversion. Because of it’s two wire construction, the power supply and signal share the same wires.

Perhaps I should try again with a 3 wire sensor, where power and signal are separated.

[Friedl]

You need to give the sensor “space to breath” (=enough voltage left), otherwise it just won’t work.

If you take this setup (from the product page):
https://www.calex.co.uk/site/wp-content/uploads/2020/01/pyromini-oem-connections-4-20-ma-1024×411.png
and add the 500 Ohm resistor across the +/- of the instrument shown in the picture, which would then be your Controllino, we can conclude:

1. 0,020 A * 500 Ohm = 10V
2. 0,004 A * 500 Ohm = 2V
3. 24V – 10V = 14V > 8V ! (24V power supply assumed)

And BTW (see datasheet):

Max. Loop Impedance
900 Ω (4-20 mA output)

Put aside your Controllino, only leave the resistor, take a digital multimeter and verify your setup first. When you know what voltages are to be measured, verifying what you measure with the ADC is much easier.

• This reply was modified 4 years ago by  Friedl. Reason: Stray DIV tags from the editor again. (PLEASE FIX THIS)

[Friedl]

When you successfully verified the sensors output voltage, you can even
replace the sensor and the resistor with a lab power supply. This makes verifying your code much easier.

[Grimmie]

Thanks for the tips, I will certainly give it a go!