Measurement Computing PC104-PDISO8 - Manual (Page 14)

4.2 FORM A RELAY OUTPUTS
Shown here is the schematic for a form A
relay, used at OP5 through OP7.
The form A relay has a COMMON and a
normally open (NO) contact.
When a 0 is written to the output, the
common and NO are NOT in contact. When
a 1 is written to the output the common and
NO are in contact.
Figure 4-4 Form A Relay
The form A and form C relays are actually the same part number. Only the
connections to the relay poles differ.
The Pin numbers shown in Figure 4-4 correspond to the 37 pin connector when using
an adapter such as the BP40-37 or the C40-37F-2 cable for relay #5.
4.3 ISOLATED INPUTS
There are eight optically-isolated input channels. The schematic of a single channel is
shown in Figure 4-4.
Figure 4-4. Input Circuit - Simplified
Input signals are fed to a bridge rectifier so that the inputs are not polarity-sensitive.
10
Optical
Isolator
455 Ohm