Xylem XL Series H-522 - Plus - Manual (Page 100)

11-6 Analog Inputs / 5 Volt Excitation
XL™ Series
Example #2: Now look at an example were the minimum voltage does not go to 0.00 volts.
A temperature probe with a 1 to 5 Volt output for a temperature range of !50E to +50E Celsius
would have the following setup. The slope would be calculated as follows:
The Offset value would be calculated using the calculated slope value, a known temperature
value in the measurement range, and the known sensor output voltage for that temperature.
The Offset value was calculated using known values. At a temperature of 60E Celsius, the
temperature probe output will be 5 Volts. Also at a temperature of -40E Celsius, the temperature
probe output will be 0 Volts.
Notice here the minimum voltage is no longer 0.00 and the offset does not equal the minimum
sensor value as in the first example.
In both examples there were two temperature values that we also knew the corresponding
voltages. Knowing these values allows us to calculate the slope and offset based on what is often
called a two point calibration. The next section describes more in theory the two point
calibration process.