Measurement Computing CIO-PDISO16 - Manual (Page 14)

13
Chapter 3
Functional Details
Form C relay outputs
The Form C relay has a common, normally open (NO) and normally closed (NC) contact. Figure 6 shows the
schematic for a Form C relay.
19
37
18
NORMALLY OPEN
COMMON
NORMALLY CLOSED
Figure 6. Form C Relay (0) contacts
 When 0 is written to the output, the common and NC are in contact.
 When 1 is written to the output, the common and NO are in contact.
Isolated inputs
The CIO-PDISO16 has sixteen isolated input channels. A schematic of a single channel is shown in Figure 7.
1.6 K
Isolated input
not polarized
Circuitry sharing
PC Ground
Filter switch
0.1 uF
47 K
+5 V
100 K
Figure 7. Isolated input schematic – simplified
The signals are routed through a bridge rectifier so that the inputs are not polarity sensitive. When a voltage is
present at the input than the "input high" threshold, a logical "1" will be sensed for that input.