Section 1
ZGARD S & DS Gas Sensors
General Information and Applications
The ZGARD S Sensors are designed to detect the presence of Carbon Monoxide, Nitrogen Dioxide, Refrigerants or
Ammonia in air. The EC type employs electrochemical plug-in cells. The solid-state (SS) type employs Metal Oxide
Semiconductor (MOS) sensing technology. Each sensor generates a representative output signal proportional to the
calibrated operating range.
The ZGARD DS is a Dual Sensor in one enclosure and both sensors employ Electrochemical (EC) plug-in cells. The ZGARD
DS sensor is designed to detect the presence of Carbon Monoxide and Nitrogen Dioxide in air.
The ZGARD S & DS sensors are available with two output versions, a 4-20mA analogue output or an addressable RS485
digital signal. The ZGARD S & DS, RS485 version is specifically designed to operate with any MSA ZGARD C 485
Controllers, operating as a system. The ZGARD S & DS with 4-20mA output can be installed as a stand-alone sensor
typically integrated with common commercial equipment including PLC, DCS or Building Environmental Automation
Systems.
The table below provides the distinctive features of the ZGARD S & DS Sensors. This is a quick guide for
determining the operating features of each sensor.
ZGARD S & DS
SENSORS
CARBON
MONOXIDE (SS)
CARBON
MONOXIDE (EC)
NITROGEN
DIOXIDE (EC)
REFRIGERANTS
(SS)
AMMONIA (SS)
Principal of
Operation
MOS, Metal Oxide
Semiconductor
Electrochemical Electrochemical
Metal Oxide
Semiconductor
Metal Oxide
Semiconductor
Operating Range
0-100ppm
OR
0-200ppm
0-100ppm
OR
0-200ppm
0-10ppm
0-1,000ppm 0-500ppm
On-Board Test
50 & 100% Full
Scale Output Test
jumper
0 & 100% Full Scale
Output Test jumper
0 & 100% Full Scale
Output Test jumper
50 & 100% 0Full
Scale Output Test
jumper
50 & 100% Full
Scale Output Test
jumper
Output
4-20mA
OR
RS485 Network
4-20mA
OR
RS485 Network
4-20mA
OR
RS485 Network
4-20mA
OR
RS485 Network
4-20mA
OR
RS485 Network
Calibration
Zero and Span
Potentiometers
Zero and Span
Potentiometers
Zero and Span
Potentiometers
Zero and Span
Potentiometers
Zero and Span
Potentiometers
Cut-Off Feature 17ppm NONE NONE 65ppm 50ppm
Periodic inspections and calibration: This unit requires calibration. The calibration frequency will be a function of the operating conditions,
including operating under extreme temperatures, exposure to contaminants or gas concentrations greater than the lower explosive limits. A
calibration inspection must be included as part of a routine maintenance to ensure proper operation of the gas detection unit. If unit span or
zero cannot be adjusted, the sensor may be approaching its end-of-life or has been contaminated and must be replaced.
The performance of any ZGARD S & DS Sensor is dependent on the appropriate and strategic placement within a guarded
area. The remote gas sensors should be strategically placed closest to the areas where the target gases or vapors might
occur in the atmosphere. Follow the recommended guidelines listed below.
Determination of number of sensors: The number of transmitters required is determined by a unit’s operational radius of
surveillance. Using table below, the number of units required can be easily evaluated.
Gas Detected
Radius of Surveillance Guarded Area
CO Carbon Monoxide, NO2 Nitrogen Dioxide 50 feet (15 meters) 7,854 square feet (707 square meters)
Refrigerants, Ammonia 23 feet (7 meters) 1,662 square feet (154 square meters)
Surface-mount installation: Installation of the sensor simply requires the physical mounting of the enclosure and
connection of the power and output lines.
Target Gas
Relative Density (air = 1) Recommended Height
CO Carbon Monoxide 0.968 3 - 5 feet (1 - 1.5 m ) from floor
* NO2 Nitrogen Dioxide 1.58 (cold) 1- 3 feet (30 cm to 1 m) from ceiling
R11 Refrigerant 5.04 1 foot (30 cm) from floor
R12 Refrigerant 4.20 1 foot (30 cm) from floor
R22 Refrigerant 3.11 1 foot (30 cm) from floor
R134a Refrigerant 3.52 1 foot (30 cm) from floor
NH3 Ammonia 0.59 1 foot (30 cm) from ceiling
* May differ in certain applications. Hot NO2 from exhaust systems is lighter than ambient air.
1.0
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