©
National Instruments Corp.
9
FP-DI-330 and cFP-DI-330
Figure 10 shows the input circuitry for a single channel.
Figure 10.
[c]FP-DI-330 Input Circuit
Sensing DC Voltages
When an external device applies a positive or negative DC voltage
with a magnitude of at least 4 V across the IN
a
and IN
b
terminals,
the [c]FP-DI-330 registers an ON condition. The [c]FP-DI-330
limits the current drawn by the input circuit to approximately
1.5 mA for voltages up to 250 V.
When an external device applies a voltage with a magnitude of less
than 1 V to the IN
a
and IN
b
terminals, the [c]FP-DI-330 registers
an OFF condition. When the external device applies a voltage
between –4 and –1 V or between 1 and 4 V, the [c]FP-DI-330 may
or may not register an ON condition.
Ensure that the devices you connect to the [c]FP-DI-330 have
OFF-state leakage currents lower than 350
µ
A. Higher leakage
currents can cause false ON readings.
The filter on the [c]FP-DI-330 inputs cause a delay of
approximately 1.2 ms between the time a voltage changes from the
ON state to the OFF state and the time the [c]FP-DI-330 recognizes
the change. The delay for a transition from an OFF to an ON state
is approximately 0.2
µ
s.
Sensing AC Voltages
The [c]FP-DI-330 senses a wide range of AC signals. The
minimum ON-state voltage for an AC signal depends on the
frequency of the signal. When an external device applies a voltage
between 1 V and the minimum ON-state voltage across the input
terminals, the channel may or may not register an ON condition.
IN
a
V
SUP
COM
IN
b
V
C
Status
Indicators
Optical
Isolation
[c]FP-DI-330
Current
Limiter
AC Smoothing
Filter
