Measurement Computing PCI-PDISO8 - Manual (Page 11)

PCI-PDISO8 User's Guide Functional Details
11
Isolated inputs
The PCI-PDISO8 has eight isolated input channels. A schematic of a single channel is shown in Figure 8. The
signals are routed through a bridge rectifier so that the inputs are not polarity sensitive.
Figure 8. Isolated input schematic - simplified
Extending the input range
To extend the input range beyond the 5 V to 28 V specified, add an external resistor. Figure 9 shows the resistor
and the equations used to calculate resistor values for a given V
in
.
Figure 9. Input range-extending resistor
For more information on digital signal connections
For more information on digital signal connections and digital I/O techniques, refer to the Guide to Signal
Connections. This document is available on our web site at available on our web site at
www.mccdaq.com/signals/signals.pdf ).
AC input filter
The inputs are eight individual, optically isolated (500 V) inputs that can be read back as a single byte. The
inputs are not polarity sensitive and may be driven by either AC (50 Hz to 1000 Hz) or DC.
Each input has a software enabled/disabled low-pass filter with a time constant of 5 ms (200 Hz). You enable or
disable each input with InstaCal. The filter is required for AC inputs, and should be used for almost all DC
inputs. Unless you have reason to turn off a filter, you should enable it.