Pepper Computer Modular Computers RS485 - Manual (Page 123)

SMART I/O User’s Manual Chapter 4 Digital Modules
©1996 PEP Modular Computers GmbH March 12, 1996 Page 4 - 35
4
The individual relays are low active which means that a digital ‘0’ delivered
by the system closes the relay and illuminates the LED on the front-panel
corresponding to the required channel. Conversely, a logical ‘1’ appearing
on the external VCC line suggests that this supply is connected and active.
The operational life of the relays is recorded in terms of operating cycles and
refers to mechanical failure. The contacts however could be damaged
through excessive load switching causing sparks to break down the contact
surface. This in turn could increase the resistance and lead to an MTBF that
is shorter than that quoted in the specifications.
256 bytes of serial EEPROM contain the module ID number and production
data although space has been allocated for future use.
Load
Com. Ext. Vcc
Com. Ext. Gnd
LED
Driver
Digital
Output
System
Interface
Relay 24V DC
4.3.5 Functional Description
Figure 4.3.5.1: SM-REL1 Schematic Diagram