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The 20 mA current level
must
be set to an H
2
S reading level before the 4-20 mA
connection can be used. This value can only be set at the 651, and cannot be set using
Jerome Monitor Software (JMS).
•
Select 4-20 MAX from the SAMPLE menu to assign the H
2
S concentration (in
ppm) for the 20 mA level.
After the 20 mA level has been set, the following equation can be used to determine the
H
2
S reading based on the level of current.
H
2
S concentration detected = (current in mA - 4) x (4-20 MAX value)/16
For example, if the 4-20 MAX value is set to 50 ppm, the equation becomes:
H
2
S = (current in mA - 4) x (50/16)
Thus, in this example using a 4-20 MAX value of 50 ppm, a 20 mA current corresponds
to an H
2
S concentration of 50 ppm, while a 12 mA current corresponds to an H
2
S
concentration of 25 ppm.
The 4-20 mA connection is passive and must be powered by an external 12 V DC
power supply. An example setup is shown below.
