4-20mA current loop

[chronowerxs]

Hi!

Can this raspberry pi hat be used to read out 4-20mA current loop sensor devices?

Best regards,

Robert

[Daniel-R-B]

Hi @chronowerxs , it is a bit late but i hope, i can help you or some one else a bit. I am using this hat since 2 Months.

I think it is not possible to messure the 4-20mA directly. But, it is possible to messure it indirectly. You only have to take a burden and messure the Voltage over it.

I hope the following sketch helps:

              Input Voltage
 |+                                    A-
 V                                      |
Sensor --4-20mA -> ----|Resitance|--- -> 
                      |            |
                    AD0         AinCom 
                     Waveshare Hat ADC

For my System i used a 250Ohms resitance with 4-20mA.

U = R*A
U_max = 5V (Waveshare ADC)

=> 5V = R*A 

A_max = 20mA

=> 5V = R * 20mA
switch to R
=> R = 5V / 20mA = 250Ohms

greetings, Daniel