Specifications

Halogen Gas Monitor – Multi Zone
Instruction 3015-5074 7
Functional Overview
General Description
Refrigerant monitors are specified to support compliance to federal, state and local safety codes governing
refrigerant emissions. Avoiding significant refrigerant loss reduces equipment replacement costs, maintains
equipment efficiency, promotes safety, and protects the environment.
The Bacharach HGM-MZ provides continuous monitoring of refrigerant gas levels in up to 16 separate test
zones. The instrument is easily programmed to monitor a variety of gasses and independent leak (small),
spill (medium), and evacuation (large) levels may be designated for each zone. The instrument also retains a
log of previous readings that can be easily accessed for analysis.
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 4-20mA current loop board for connection to remote monitoring equipment.
The HGM-MZ 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.
Communication Options
The HGM-MZ features full two-way communications via an RS-485 interface. MODBUS RTU is the
communication 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 HGM-MZ to be setup from a
personal computer.
Please refer to the Appendix for a more complete discussion of communication protocols.
Understanding Monitoring Levels
Effective use of this instrument requires an understanding of what constitutes reasonable alarm set points for
the types of gasses monitored. Refrigerant 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
levels based on compliance to ANSI/BSR ASHRAE 15-1994 and ASHRAE Safety Code 34-1992. These
reference levels are listed in the Appendix.
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.
Response to the Presence of Multiple Refrigerants
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.
Suggested Location of Sampling Points
At the point of a refrigerant leak the gas is nearly pure. As the refrigerant is dispersed into the air, the gas
molecules diffuse, causing a dilution of the original concentration. The HGM-MZ measures the refrigerant
concentration at the sample collection point. Therefore, if the termination of the collection line is not at the
exact point of the refrigerant leak, the unit will read a diluted mixture of the refrigerant gas and air.