User's Manual

Radio/Serial Telemetry Module User Manual
Page 14 © March 2000
The -1 and -2 modules each provide four digital inputs with 5000 volt opto-isolation, suitable for
voltage free contacts (such as mechanical switches) or NPN transistor devices (such as electronic
proximity switches). Contact wetting current of approximately 5mA is provided to maintain reliable
operation of driving relays.
Each digital input is connected between the appropriate "DI" terminal and common "COM". Each
digital input circuit includes a LED indicator which is lit when the digital input is active, that is, when
the input circuit is closed. Provided the resistance of the switching device is less than 200 ohms, the
device will be able to activate the digital input.
For pulse inputs, refer to Section 2.4.6.
2.4.2 Digital Outputs (-1)
The -1 module provides four normally open voltage-free relay contacts, rated at AC3 250V/2A,
120V/5A ; AC1 - 250V/5A ; DC - 30V/2A, 20V/5A. These outputs may be used to directly
control low-powered equipment, or to power larger relays for higher powered equipment. When
driving inductive loads such as AC relays, good installation should include capacitors (e.g. 10nf
250V) across the external circuit to prevent arcing across the relay contacts. For DC inductive
loads, flyback diodes should be used to drive DC relays.