26
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Operation Theorem
4.2
Isolated Digital Input
The PCI-7256 contains 16 opto-isolated digital input channels. The circuit
diagram of the isolated input channel is shown below.
Figure 4.2 Photo Coupler
The digital input is first routed through a photo-coupler (PC3H4), so that the
connection are not polarity sensitive whether useing positive or negative
voltage.
In addition, a first order-filter with time constant about 1.5ms is provided to
filter high frequency noise. The normal input voltage range for high state is 5
to 24V.
The PCI-7256 provides an is5V power for dry contact input. When
the external circuit has no voltage source(e.g. a switch), users can use the
on board +5V to respond the change of external circuit. The maximum output
current of the on board isolated power is 170mA (@40
?
). Please pay
attention to the current consumption of the external circuit not exceeding the
limit. The dry contact architecture is shown in Figure 4.3.
Figure 4.3 Dry contact
