Ametek 303B

Overview | 1-13
The mathematics to map a specific range into another range are listed
below. This technique assumes that gain and offset are at their default
values, 1.0 and 0.0.
Actual ppm Values = Act_low and Act_high
Mapped Into Values = Map_low and Map_high
(Map_high – Map_low)
Gain = -------------------------------
(Act_high – Act_low)
Offset = (Gain • Act_low) – Map_low
In the first example the calculations are:
Actual ppm Values = 50 ppm and 100 ppm
Mapped into Values = 0 ppm and 100 ppm
(Map_high – Map_low)
Gain = --------------------------------
(Act_high – Act_low)
Gain = (100 – 0) / (100 – 50)
= (100) / (50)
= 2.0
Offset = (Gain • Act_low) – Map_low
= (2.0 • 50) – 0
= 100.0
Since the goal is to get 50 to 100 ppm to be 0 to 100 percent on the 4 to
20-mA output, the above example could have been mapped into the 0 to
10-ppm range. The following shows the calculations for mapping 50 to
100 ppm into the 0 to 10-ppm range.
(Map_high – Map_low)
Gain = --------------------------------
(Act_high – Act_low)
Gain = (10 – 0) / (100 – 50)
= (100) / (50)
= 0.2
Offset = (Gain • Act_low) – Map_low
= (0.2 • 50) – 0
= 10.0