QUESTION: How can I setup a 4-20mA sensor with EasyLogGSM ?

ANSWER: With a precision resistor to convert the current loop output into analog voltage output using these simple instructions:

1. Connect the sensor (Ex: Hukseflux SR20 D2 pyranometer) to an analog input wire terminal (Ex: A9 logger input) together with a 100 Ohm resistor whose other end is connected to Ground.

2. In the EasyLog setup software, enter the proper analog multiplier polynomial coefficients (A0, A1, A2, A3) to match the sensor’s measurement range (Ex: 0 - 1600W/m^2) and the corresponding electrical output range (Ex: 4-20mA).

3. Since the sensor is linear, on the A0 = offset and A1 = slope coefficients will be used.

4. Calculate the scaling factor as in the following Excel spreadsheet calculator and instructions:

Simply make a table, of minimum and maximum values if inputs and outputs and use the below Excel calculator:

Pyranometer range 0 W/m2 1600 W/m2
Sensor output 4 mA 20 mA
Voltage drop @ 100R 400 mV 2000 mV

Result:

A0 = -400 mV
A1 = 1 mV
A2 = 0
A3 = 0

Check:

• 0 W/m2 --> 400 mV
  Calculation with polynomial: -400 + 1 * 400 = 0 W/m2

• 1600 W/m2 --> 2000 mV
  Calculation with polynomial: -400 + 1 * 2000 = 1600 W/m2

EasyLogGSM Meteorological Data Logger Setup Photos and Diagrams

4-20mA sensors may only be connected to AIN9 - AIN12 EasyLogGSM inputs