4-20 mA Unit with wemos S2 mini ESP32

obstbauer

@felmue Hello,
thank you very much, it works !
I added

cr.begin(&Wire, MODULE_4_20MA_ADDR, 33, 18, 100000UL);

to void setup

obstbauer

it seems that I still have a problem....
I have a current reading but the value is wrong,
I get soemthing around 7.2 mA instead of 4 mA.
I can measure the 4 mA with a multimeter in the circuit and the sensor should send 4 mA, so this is ok, but the M5Stack unit shows 7.2 mA and I don't understand why ? Any ideas ?
My sensor is passive, I connected 24 V to the 4-20mA unit and all three jumpers are installed
What is the meaning of the function "getCalCurrent" ? It is neessary for the current measurement ? It is necessary to set a "ref current" ?

Thank you!

robski

@obstbauer try calibration function based on what you see with multimeter

obstbauer

@robski thanks for the answer

so you mean if I measure with multimter 4.0 mA (which is true for the sensor) and the unit shows me 7.2 mA I should set the calibrated value to 4.0 ?

Because this is not mentioned anywhere in a readme file or manual or in the description of the device, and it is not made in the example file at github
but I am a beginner....

robski

@obstbauer thats what i did with mine initially, calibrate with known current value

obstbauer

@robski ok I think I found it:

thank you I will try tomorrow

robski

@obstbauer yeah thats the registers table, I used Uiflow2 with calibration block but you are using not M5Stack controller I see

obstbauer

@robski what value do you take for "index" in the function

void MODULE_4_20MA::setCalCurrent(uint8_t index, uint16_t value)

robski

@obstbauer haven't used index value

in uiflow2 ..ain4_20ma_0.set_cal_current(10) to set 10mA
ain4_20ma_0.set_cal_current(20) to set 20mA

obstbauer

@robski yes maybe in uiflow2 but the function for the c program asks for an index and a value

obstbauer

I see really strange behaviour and I don't know the reason and I get no answers from the support.....
The example code from M5Stack say that the currentvalue should be divided by 100:

canvas.printf("Current:%.2fmA", (float)(meter.getCurrentValue(0)) / 100.0);

The values I get I have to divide by 10 to get the right current in mA.... and the other issue is that I can only use half of the measurement range, at 12.5 mA the ADC sends 65520...

maybe someone has an idea ?

obstbauer

change to a raspberry PI4 seems to be no solution too.....
it woud be nice if there would be a better documentation for people who want to use the units outside the m5stack universum....

robski

@obstbauer this is uiflow example with raw value and float too