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How to calculate and configure the Zero and Full scale value for a PM8000 Analog Input

Issue
Configuring the analog input on a PM8000.

Product Line
PM8000 series

Environment
Meter Configuration

Cause
Unlike other ION devices, the PM8000 analog input is only rated for 4-20mA rather than 0-20mA. 

Resolution
Per the ION Reference, the Zero Scale can be calculated as follow:

Zero Scale = FullScale - (FullScale - X)(Af - Ax)/(Af - Aa)

where
Aa is the analog hardware output minimum range value. (For the PM8000, Aa is equal to 4 mA.)
Af is the analog hardware output maximum range value. (For the PM8000, Af is equal to 20 mA.)
Ax is the analog hardware output minimum value. (For the PM8000, Ax is equal to 4 mA.)
X is the scaled equivalent of Aa. (This is determined by the device sending the Analog signal.)

The previous equation can be simplified to:

Zero Scale = FullScale - (FullScale - X)*(Af - Ax)/(Af - Aa)
Zero Scale = FullScale - (FullScale - X)*(20 mA - 4mA)/(20 mA - 4mA)
Zero Scale = FullScale - (FullScale - X)
Zero Scale = X

Therefore, the Zero Scale should correspond with the 4mA value.

For example, if a PM8000 meter is monitoring a 0 to 120 kW system and receiving the power information via a 4 - 20 mA analog signal, the PM8000 would need to be configured to have a Zero Scale of 0 and a Full Scale value of 120.

For instructions on programming the Zero Scale and Full Scale values, please consult page 110 of the PM8000 User's Manual.
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