Multi-Tech Systems 7500 - Manual (Page 229)

ION 7500 / ION 7600 User’s Guide Setting Analog Zero and Full Scale Values
Digital and Analog I/O Technical Note Page 229
Determining the Zero Scale setting for output ranges below zero
To determine the Zero Scale setting for any range of output (e.g. -1000 W to 1000 W)
use the Zero Scale multiplier to calculate the portion of the entire range that falls
below the lowest expected value. When you subtract this portion of the range from
the lowest expected value the result is entered as the Zero Scale setting:
For example, assume the output type is 0 to 20 mA, the desired range is 4 to 20 mA,
and the minimum and maximum expected values are -1000 W and 1000 W:
Enter -1500 in the Zero Scale register. When the value drops to its lowest expected
value of -1000 W the current output is 4 mA as illustrated below:
ZeroScaleValue MinimumValue ZeroScaleMultiplier Maximum Minimum – ( ) – =
1500 – 1000W – 0.25 1000W 1000W – ( ) – ( ) – =
-1500 W 0mA
-1000 W 4mA
1000 W 20mA