Specifications

Multi-Zone Gas Monitors
4 P/N: 3015-5074 Rev 13
An audible alarm and front panel indicators are provided to signal alarm and fault conditions, and relay
contacts are provided that can be used to trigger external alarm devices in the event of a system fault, or if a
leak (small), spill (medium), or evacuation (large) level of gas is detected. The system also may be fitted
with and optional two-channel 4-20 mA current loop board for connection to remote monitoring equipment.
The multi-zone monitor requires only minor periodic maintenance such as the occasional replacement of
filters. The monitor incorporates active diagnostics that continuously check the system for proper operation.
A front panel indicator is provided to alert an operator of system malfunctions, and fault codes are generated
that enable the user to identify the cause of the fault.
1.5.2. Communications Options
The multi-zone monitor features full two-way communications via an RS-485 interface. MODBUS RTU is
the communications protocol standard. The instrument can be connected directly to a Building
Management System or it may be operated as a stand-alone system.
An RS-232C port is also provided for connection to a PC. This enables the monitor to be setup from a
personal computer. Refer to Appendix B for more information on communications protocols.
1.5.3. Understanding Monitoring Levels
Effective use of this instrument requires an understanding of what constitutes reasonable alarm set points
for the types of gas being monitored. Manufacturers define allowable exposure levels and threshold limit
values in units of parts per million (ppm). In a good “tight” installation these background levels will be
acceptably low and often do not require corrective action. You can reduce nuisance alarms and needless
service calls if the alarm levels are set at practical limits. Bacharach has developed recommended
monitoring refrigerant gas levels based on compliance to ANSI/BSR ASHRAE 15-2007 and ASHRAE
Safety Code 34-2007. These reference levels are listed in Appendix A.
Setting the monitor at these recommended alarm levels will satisfy the needs of most users. However, the
ppm levels generated by system leaks into the environment are greatly influenced by the volume of air in the
sampling area, air circulation, size of the leak, distance to the monitoring point, and a host of other variables.
In some cases the set points may need to be adjusted either up or down to achieve effective monitoring.
1.5.4. Response to the Presence of Multiple Refrigerants (HGM Only)
The HGM-MZ is a refrigerant level monitor, not a gas analyzer. You must program the monitor to test for a
specific refrigerant, and it will only return accurate concentration readings for that particular refrigerant. If
a leak occurs of another refrigerant gas type, the monitor may return incorrect readings.
Most applications only require detection of a single refrigerant and the problems that are associated with
monitoring multiple gases are rarely an issue. If there is a possibility of multiple refrigerants leaking in the
same sampling zone, then you should carefully consider which refrigerant compound you program the
unit to monitor.
1.5.5. Suggested Location of Sampling Points
At the point of a leak the gas is nearly pure. As the gas is dispersed into the air, the gas molecules diffuse,
causing a dilution of the original concentration. The monitor measures the concentration at the sample
collection point. Therefore, if the termination of the collection line is not at the exact point of the leak, the
unit will read a diluted mixture of the gas and air.
Gases of interest may be heavier or lighter than air and may collect above or below the point of the leak.
Therefore sampling point placement is critical and must take into account properties of the target gas and air
flow within the space. In general, sampling points should be located as close as possible to the sources of
potential leaks. If this is impractical, then alarm set points for that zone should be adjusted to compensate
for the dilution of the gas. General placement guidelines are shown below, but air-flow dynamics should also
be considered (e.g., consider the effects of exhaust fans which tend to draw target gas from the space).
• HGM-MZ Halogen Mount sampling points 6-18 inches above floor
• AGM-MZ NH
3
(Ammonia) Mount sampling points 1-2 feet below ceiling
• CO
2
-MZ CO
2
(Carbon Dioxide) Mount sampling points 4-6 feet above floor (breathing zone)