Open-Loop Detection - National Instruments FP-AO-200 Operating Instructions Manual

Using an external COM connection may be more convenient in
your application than using the COM and C terminals on the
terminal base or connector block. Figure 5 shows how to connect
to two channels using an external COM connection.
V
[c]FP-AO-200
Figure 5. Connecting to Two Channels Using an External COM Connection
Output Ranges
You can configure each channel independently for an output range
of either 0–20 mA or 4–20 mA. The default power-up setting for
each channel is 0–20 mA, with the output set to 0 mA. The
[c]FP-AO-200 has overranging of 0.5 mA in each of these ranges,
so that the actual full-scale ranges available are 0–20.5 mA and
3.5–20.5 mA. Overranging enables the [c]FP-AO-200 to
compensate for span and offset errors in field devices.

Open-Loop Detection

Each channel has a monitoring circuit that compares the actual
output current to the specified output current. If the [c]FP-AO-200
cannot source the specified output current for one or more
channels, the monitoring circuits turn on a red STATUS LED for
each affected channel and report the error condition to the network
module. Generally, the error condition is caused by an open current
loop—either the load device or the loop supply is disconnected.
However, the monitoring circuit also detects errors caused by load
impedances that are too high and by loop supply voltages that are
too low.
If the output of a [c]FP-AO-200 channel is set to 0 mA, the
monitoring circuit does not register an error condition because the
FP-AO-200 and cFP-AO-200
C
I
out
COM
I
out
COM
Load
Load
6
+
Loop
Supply
–
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