105 Radio/Serial Telemetry Module
User Manual
Page
16
©
January 2004
2.4
Input / Output
2.4.1
Digital Inputs (105-1, 105-2 and 105-4)
The 105-1 and 105-2 modules each provide four digital inputs with 5000 volt opto-isolation, and the
105-4 provides 4 – 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 (105-1)
The 105-1 module provides four normally open voltage-free relay contacts, rated at AC3 50V/2A, ;
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.
Digital outputs may be configured to individually turn off if no command message is received to
that output for a certain period. This feature provides an intelligent watch dog for each output, so
that a communications failure at a transmitting site causes the output to revert to a known state. See
section 4.4 Changing User Options
for further details.
_
+
DO 1
DO 2
105U
Max 50VAC
5A
AC
Load
DC
Load
Max 30VDC
2A
+
_
DI 1
DI 4
COM
105U
Voltage-free
contact input
Transistor
input
V
+
V
-
