Pinnacle Systems MG - Manual (Page 9)

The Microguard is the latest in infrared safety curtain
technology. Contained in the main housing (Controller
Module) is a diverse redundant architecture that is
designed to detect internal failures in the Emitter
pylon(s), Receiver pylon(s), and the Controller Module
which will immediately send a “STOP” command to
the machine, thus being “FAIL-SAFE.” Failures are
immediately reported on the diagnostic message display
for immediate evaluation.
Diverse redundancy means that there are at least two
ways to detect a system failure, two ways to shut it down,
and that the two methods of detection and shut down
use different techniques. This eliminates the chance
an inherent fault in one circuit will effect the other. For
example: The stop circuit output contacts run through
two relays and both are monitored for correct position
through a second set of contacts on each relay. A special
circuit monitors those contacts, but a different circuit (a
test circuit) monitors the first circuit to make sure that it
is functioning correctly. Two different microprocessors
isolated from one another each monitor the same signals
and monitor each other. Either microprocessor can turn
off the output relays, but it requires both to turn them on.
Special watchdog circuits on the microprocessors and
on the output relay circuits prevent an unsafe condition
by turning off both outputs relays should either or both
microprocessors become erratic.
With the aid of advanced microprocessor technology, the
MicroGuard can not only detect a fault in the light curtain
but spell out the exact problem. This advancement is
a great help during alignment, use, and servicing of the
light curtain. It not only can detect shorted and open
infrared emitters, but indicate which emitters have failed,
allowing the faulty board to be replaced.
Built into the MicroGuard is an optically coupled external
relay check which can detect open or short circuits,
a Cincinnati Interface, provision for auxiliary output
contacts, and external voltage check input. The power
supply is designed to accommodate most voltage
requirements, from DC to AC (see Specifications).
As the MicroGuard is a single function device, that of
sensing an unauthorized intrusion into a guarded area
while simultaneously determining that it is capable of
sensing such an intrusion, any internal malfunction will
manifest itself with a RED condition shut down.
Theory of Operation. The MicroGuard guards an area
by projecting a curtain of infrared light across it. It forms
a curtain by utilizing infrared emitters in line very close
together on .5” or 1” centers. This close spacing makes
it impossible to place a body part through the curtain
without detection. For every infrared emitter there is an
infrared detector directly opposite. When an obstruction
is placed between them, the beam is broken and the
absence of a beam is observed by the Controller Module
which de-energizes the output relays and opens the
circuit it is connected to.
The System. The MicroGuard employs infrared
technology in a small sealed NEMA 4 aluminum housing
which provides harmless invisible protection and an
unobstructed view of the guarded area. The Microguard
consists of three parts: an Emitter pylon(s), Receiver
pylon(s), and Controller Module. The Emitter pylon(s)
contains infrared light emitting diodes spaced .5” or 1”
apart down the entire length of the pylon. The Receiver
pylon(s) contains an equal number of infrared detector’s
and transistor receivers also spaced .5” or 1” apart.
The Controller Module contains diverse redundant
technology that includes two different microprocessors,
self-checking circuitry, power supply, safety output
contacts, and a diagnostics display.
System Safety. The MicroGuard employs diverse
redundant technology that provides a backup for every
system that could cause an unsafe condition. Upon
power up, all systems are checked before activating
the output relays. Once the unit passes the initial
tests and activates the system it is then tested by both
microprocessors and other circuits once per scan of
the light curtain. All signals are presented to both
microprocessors, but are isolated from one another
to prevent a failure of one microprocessor should the
other crash. Other circuits detect short circuits, open
circuits, proper voltage, proper oscillation, etc. The
use of special dual force guided safety relays assure
that if one fails, the other can safely shut down the unit.
Additionally, watchdog circuits on the relays prevent an
unsafe condition even if both microprocessors failed.
All the standard and optional features that run on the
MicroGuard are designed with safety in mind:
The Floating Blank option allows only one object to be
placed into the light curtains field of view. Even if the
object is smaller than the allowed size, a second object
will cause the unit to go RED.
The Auto Blank option programs in the exact size and
location of an object automatically and thus can detect
any movement in the object and shut down the light
curtain, which must be reset with a key.
The External Relay Check can detect both an open or
a short in the external relay or its wiring. The standard
Cincinnati Interface provides a means to assure that
the light curtain can open up its output relays
between press cycles.
Introduction
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