SPX+ Introduction Manual - updated until firmware 4997
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Information on Dry Contact cables: The extension length of the Dry Contact twisted pairs is limited
only by the amount of electromagnetic noise in the area. So the lengths can be quite long, but long
cable lengths may create occasional false positives. These false positives can be eliminated with the
advanced filtering of the Dry Contact sensor on the system. You can define how long a sensor must
be in the error condition before changing state from Normal to Critical. You can also define how long
the sensor must remain in the Normal state before changing from Critical to Normal.
Isolated Dry Contact details
The standard Dry Contacts are as in Fig. 1: directly connected to the unit’s controller board.
In this setup, power is provided by the sensorProbe+ to the switches. With the sensorProbe+
providing the power, the switch has +5 Volts applied to pin 1 and GND applied to pin 2. When the
switch is open, the input senses +5. When the switch closes, the input senses GND. No additional
external power is needed.
Fig. 2 shows the optional opto-isolated Dry Contact mode. This provides complete electrical
separation between the sensorProbe+ and the dry contact. The sensorProbe+ is therefore protected
against possible large voltage spikes caused by lightning for example.
Note that the maximum voltage that can be applied to the dry contact inputs in opto-isolated mode is
30V DC. This will protect these inputs and the unit from high voltages and spikes.
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