EKO INSTRUMENTS CO., LTD. 4-20mA Signal Converter MC-11 Instruction Manual V1
Pg. 11
5-3. Measurement
1. Calculation of Solar Irradiance from Current Output
Current conversion
Only for pre-set solar sensitivity values (4-20 mA = 0 – 1600 W/m
2
).
To convert the mA output signal into the measurement unit [W/m
2
] the following formula has to be used:
I = (Iout – 4mA) x 100
Where:
I
= Solar Irradiance [W/m
2
]
Iout
= Measured Current [mA]
Voltage conversion
Only for pre-set solar sensitivity values (4-20 mA = 0 – 1600 W/m
2
).
Measure the voltage across the precision shunt resistor, which is connected in series with the 4-20mA output
cable. To convert the V output signal into the measurement unit [W/m
2
] the following formula has to be used:
I = (V / R * 1000 – 4mA) x 100
Where:
I
= Solar Irradiance [W/m
2
]
V
= Measured Voltage [V]
R
= Precision Shunt Resistance [
Ω
]
Example:
a) When 50
Ω
resistance is used, the voltage at the both ends of the shunt resistance would be 200mV
to 1V, and it is equivalent to 0 to 1600W/m
2
b) When 500
Ω
resistance is used, the voltage at the both ends of the shunt resistance would be 2V to
10V, and it is equivalent to 0 to 1600W/m
2