SMA SC 200 - Manual (Page 50)

Analog Inputs SMA Solar Technology AG
50 SC-BEN100262 User Manual
9.2 Calculating Gain and Offset
Calculating gain and offset using the example of "ExtSolIrr".
1. Detecting external sensors as described in Section 9.1 ”Detecting External Sensors” (page 49).
2. Set "ctrl ExtSolIrr" to "on" to activate the analog
input for the sensor.
3. Select a measurement range for the analog sensor ,
e.g. "+/-10V".
The displayed value is calculated by means of the
following:
– the value measured by the sensor
– the value indicated for gain
– the value indicated for offset
4. Calculate the gain factor and the offset.
The gain factor is obtained by dividing the display range by the measured range.
Gain factor = display range / measured range
The offset is calculated by subtracting the product of gain factor x lower limit of measured range
from the lower limit of the display range.
Offset = lower limit of display range - (gain factor x lower limit of measured range)
Formulae
M is a value measured in a range between Ml and Mu.
D is the value to be displayed in a range between Dl and Du.
Explanation of the abbreviations used
Gain: G = (Du - Dl) / (Mu - Ml)
Offset: O = Dl - (G x Ml)
Display on the Sunny Central Control: D = (G x M) + O
M measured value Mu upper limit of measured range
Ml lower limit of measured range O Offset
G Gain D Display value
Du upper limit of display range Dl lower limit of display range