Serial Watchdog
4
0 Introduction
This document describes the installation and the principle of operation
of a watchdog monitored computer system consisting of the GBS-
Elektronik Serial Watchdog, an industrial PC and an optional UPS. Such
an arrangement is required for autonomously working unattended
measurement systems. The UPS buffers a short main power loss and is
able to clearly shut down the computer if the main power does not
return. During normal operation the Serial Watchdog monitors the
computer via the RS232 interface. If the computer hangs because of a
software crash or a hardware trouble, the watchdog does not receive
the ping signal any longer and tries to restart the computer: First by
initiating a Windows Software restart and, if this doesn’t work, by
breaking its power supply for a short time. A small program runs
permanently on the computer in the background and sends periodically
the ping signal over the serial port as long as everything works perfectly.
The system state is always indicated by several LED's at the watchdog's
front and by an external lamp.
The great advantage of the Serial Watchdog is its hardware
independence. It is suitable for almost all computers which are equipped
with a serial RS232 interface. Other watchdog monitored computer
systems require a special computer hard- and software. These systems
are often expensive and inflexible.
1 Installation
The Serial Watchdog is usable in different situations. It works with 230V
AC computers and with 24V DC systems, too. The two most important
installation variants are described in this chapter. The watchdog design
allows a maximum of flexibility. Dependent on the situation it is possible
to modify one of the standard systems.
Mechanical installation of the watchdog unit is easily possible by
mounting it on a DIN-Rail. If no DIN-Rail is available or there is not
enough space in the facility, the watchdog has to be fastened in any
other way dependent on the situation. The open side of the
communication cable must be connected to the watchdog as described
on the SUB-D9 connector (RxD with RxD...) and the SUB-D9 connector
has to be connected to the computer which should be monitored.