National Instruments Isolated Current Output Module SCC-CO20 - Manual (Page 9)

© National Instruments Corporation 9 SCC-CO20 Isolated Current Output Module User Guide
Note Normally you would adjust to 0
μA in order to calibrate the offset, but because
the SCC-CO20 cannot source current, it is impossible to know when you have adjusted
past 0
μA.
Using the SCC-CO20
The SCC-CO20 is a 0 to 20 mA programmable current sink. The current
output is controlled by AO (X), a 0 to 10 V unipolar DAC output channel
of an E/M Series DAQ device. The relationship between the AO (X)
voltage level and the current output of the SCC-CO20 is linear and is
described by the following equation:
where
V
AO (X)
is the AO (X) voltage level.
I
CO20
is the SCC-CO20 current output in amperes.
The current sink is an N-channel power MOSFET sink to an isolated
ground reference. You can use the SCC-CO20 with industry-standard
0 to 20 or 4 to 20 mA current loops.
Note The current sink does not source current. If the input voltage is 0 V or less,
the module sinks 0 mA.
Isolated Ground Reference
Each SCC-CO20 module is referenced to its own isolated ground. Each
isolated ground can have up to 60 VDC of common-mode voltage between
itself and any other channel ground or chassis ground. Refer to the
Connecting the SCC-CO20 to a Load section for different ways to use
the isolated ground in signal connections.
V
AO X ( )
500
---------------- I
CO20
=