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CHAPTER 1. DESCRIPTION
1.1 ZoneGuard
capabilities
The ZoneGuard is a microprocessor based fixed gas
detection system designed to accept the input from a single
oxygen, combustible gas or toxic sensor. ZoneGuard
systems are designed to provide continuous round-the-clock
monitoring for a variety of common atmospheric hazards
including oxygen deficiency and/or enrichment, combustible
gases and vapors, and specific toxic contaminants such as
carbon monoxide (CO), hydrogen sulfide (H
2
S), sulfur
dioxide (SO
2
), chlorine (Cl
2
), chlorine dioxide (ClO
2
),
phosphine (PH
3
), and nitrogen dioxide (NO
2
). Sensors may
be integrally mounted to the ZoneGuard controller housing,
or located up to 50 feet away from the controller. Remote
detector assemblies are available in explosion-proof or non-
explosion-proof versions. (Combustible sensors may only
be mounted in explosion-proof sensor housings.) The unit is
designed for operation via 120VAC 60 Hz. external power
source.
Standard features include two independently adjustable
alarm setpoints, built-in loud audible alarm (85 dB at 3-feet),
easily-read, backlit LCD display, and bright LED alarm light
indicators for OK / power on (green), low alarm (amber) and
high alarm (red) conditions. Standard features also include
DPDT relay contacts (rated 5A at 250V non-inductive load)
for low and high alarm conditions. Optional accessories
include externally mounted high intensity strobe lights and
high intensity horn.
The ZoneGuard offers a choice of two modes of operation,
Text Only (“OK”), and Basic (numeric readings) to provide
the right amount of information for users with different skill
levels and monitoring requirements. Biosystems’ “One
Button” operating logic allows all procedures necessary for
normal day-to-day operation, including fully automatic
calibration adjustment, to be made through the use of the
single On/Off “Mode” button.
ZoneGuard sensors which are installed in explosion-proof
remote detector housings are classified by Underwriters
Laboratories, Inc. and the Canadian Standards Association
as Explosion-Proof for use in Class I, Division 1, Groups A,
B, C, D, E, F and G hazardous locations.
Each ZoneGuard system includes the controller with all
standard alarms, relays and electronics installed in a NEMA
4X fiberglass housing; sensor, mounting ears, calibration
adaptor, Reference Manual, Quick Reference Card, and
other standard accessories. Remote detector assemblies
include the remote sensor housing, the appropriate amplifier
board (installed in the remote detector housing), and sensor.
Note: Conduit, wire and other components necessary
to connect the remote detector assembly with the
instrument controller are not included and must be
ordered separately.
The ZoneGuard design includes many user selectable
features and is designed to be easily customized to meet
specific customer requirements. This chapter discusses
some of these special features as well as basic capabilities
used on a day-to-day basis.
1.2
Method of sampling
Once it has been connected to a power source and placed
in normal operation, the ZoneGuard system continuously
monitors for the hazard the sensor is designed to detect.
ZoneGuard sensors may be either integrally mounted to the
controller housing, or remotely located up to 50 feet away
from the controller. The atmosphere being measured
reaches the sensor by diffusing through a protective filter
into the sensor. Normal air movements are enough to carry
the sample to the sensor. The sensor reacts to changes in
the concentration of the hazard being measured. Values
are constantly updated and displayed on the ZoneGuard
controller LCD.
1.2.1 Wiring
recommendations
For oxygen remote detectors use (minimum) 22 gauge
AWG, 6 conductor twisted-pair shielded with drain. For toxic
remote detectors use (minimum) 22 gauge AWG, 4
conductor twisted-pair shielded with drain. For combustible
remote detectors use 18 gauge AWG, 4 conductor twisted-
pair shielded with drain.
The maximum distance a ZoneGuard remote detector may
be located from the controller is 50 feet.
1.3 Sensor
options
ZoneGuard systems can be configured to monitor for a
number of different atmospheric hazards. The hazard the
system is configured to detect is determined by the type of
sensor installed. The types of sensors currently available
include a galvanic oxygen (O
2
) sensor, a catalytic-bead
pellistor for LEL combustible gas, and substance-specific
electrochemical sensors for carbon monoxide (CO),
hydrogen sulfide (H
2
S), sulfur dioxide (SO
2
), chlorine (Cl
2
),
chlorine dioxide (ClO
2
), phosphine (PH
3
), and nitrogen
dioxide (NO
2
). Oxygen readings are given in percent-by-
volume, combustible gas readings in percent LEL, and toxic
gas readings in PPM (parts per million) or 0.1 PPM
concentrations.
1.4 Calibration
ZoneGuard systems have been designed for easy
verification of accuracy.
The accuracy of the Zoneguard
should be checked periodically with known
concentration calibration gas. Failure to check
accuracy can lead to inaccurate and potentially
dangerous readings.
1.4.1 One Button Auto Calibration
Biosystems’ “One Button” logic means that all normal day-
to-day operating procedures, including automatic calibration
adjustment, may be made through the use of the single
On/Off Mode button.
Calibration procedures are discussed in detail in
Chapter 3.
