905U Wireless I/O Module User Manual
105S Serial I/O Module
Page 18 © January 2011
2.3.5 24V Regulated Supply
Each module provides a 24V DC regulated supply for analog loop power, except for 905U-4/105S-4.
The supply is rated at 150mA, and should only be used for powering analog loops.
2.4 Input / Output
2.4.1 Digital Inputs (905-1, 905-2 and 905-4)
The ”-1” and ”-2” modules each provide four digital inputs with 5000 volt opto-isolation, and the ”-4”
provides 4 to 16 inputs with 3000 volt surge protection. All inputs are suitable for voltage free contacts
(such as mechanical switches) or NPN transistor devices (such as electronic proximity switches). PNP
transistor devices are not suitable. 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 ”-1” module provides four normally open voltage-free relay contacts, rated at AC 50V/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 across DC relays.
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