User's Manual

Chapter Two Installation
man_905_2.0.doc Page 17
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 (905-1)
The 905-1 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.
Digital outputs may be configured to individually turn off if no command message is received to that