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page 38 Model 2002
8.2 Operation
The 4-20 mA output option board provides dual channel current output linearly proportional to
the HPM 2002’s pressure reading. The first channel corresponds to the higher pressure range (0-
1024 Torr). The second channel corresponds to the lower pressure range (0-1000mTorr). The
equations below give the output currents for a given pressure:
Note that for both channels, the output is always between 4mA and 20mA. Specifically, when the
pressure is below 1 Torr, channel 1 current will be approaching 4mA. Also, when the pressure is
above 1 Torr channel 2 current will be saturated at 20mA.
3
8
7
Channel 1Channel 2
Internal loop
power out
Loop in
Internal loop
power out
Loop in
Figure 8.2
16mA
1000 mTorr
I(Channel 2) = 4 mA + (P(mTorr))* ( )
16mA
1024 Torr
I(Channel 1) = 4 mA + (P(Torr))*
( )
1