Filter
Top Products
SDM-SW8A Switch Closure Input Module
forces a watchdog reset by addressing the Module and requesting sufficient
information to cause a minimum of 65 clock line transitions. Advantages to
the trapping routine are:
• The bombed processor is detected before erroneous values (-99999) are
included in subsequent processing.
• The processor may be reset sooner.
• The time of processor failure may be logged by the datalogger.
• Number of failures may be logged.
A trapping routine, as described above, is included in the example program in
the Appendix.
8. Measurement Applications
8.1 SPDT Switch Closure
Single-pole double-throw switches may be found on some flow or volume
sensors such as Watt-hour and water meters. The positive throw is connected
to the 5 V terminal located next to the input channel, providing a 5 V bias for
the SW8A to discriminate between throws. Similarly, the negative throw is
connected to a ground terminal (refer to Figure 2, SPDT wiring example).
When contact is made to the positive throw, SW8A circuitry holds a high state
(5 V). When contact is made with the ground throw, a low state is maintained
(0 V). Switch bounce may occur any number of times at a throw, but until
contact is made with the opposite throw, a change in state will not occur. The
pole must make contact with the throw for 3 ms for a state change to occur.
Figure 3 illustrates a raw SPDT signal in relation to the signal conditioned by
the SW8A.
FIGURE 3. SPDT Signal Conditioning by SDM-SW8A
The 5V output located next to each of the 8 input channels is for
biasing in the SPDT measurement. A 200 Ohm resistor is in
series to protect against accidental shorting to ground.
NOTE
10