ENMET ISA-44-RAL-OD - Manual (Page 5)

ISA-44RAL-OD / ISA-44RAH-OD ENMET Corporation
1
1.0 Introduction 1.0 Introduction
Sandblasting, welding and spray painting are examples of activities that create potentially hazardous environments.
Such environments contain toxic gases, dust and fumes. An air compressor system with hoods or masks supplies clean
breathing air to workers and minimizes the risk of injury or death; however, carbon monoxide (CO) can contaminate
the air in a compressor system. Carbon monoxide contamination can occur either when the intake air itself is
contaminated, or when the compressor breaks down and overheats. Because of this hazard, Federal OSHA regulations
(Sec. 1910.34) require monitoring of CO in compressed air systems. In addition, the Compressed Gas Associations
has set up guidelines governing maximum tolerable levels of CO and other contaminants (Spec. G-7.1) to ensure the
health and safety of persons who use respiratory air lines.
The ENMET ISA-44RAL-OD monitors the carbon monoxide and oxygen levels in compressed air used for human
breathing. If the CO concentration exceeds any predetermined levels, the ISA-44RAL-OD will trigger audio-visual
alarms and activate any associated equipment to alert personnel in potential danger. In addition, if the oxygen
concentration falls below a predetermined level, the instrument will again alarm in the same manner.
This instrument is designed to operate continuously; there is no on/off switch. Therefore, the ISA-44RAL-OD should
be left on 24 hours a day. The instrument should not be unplugged at night or at the end of a workshift. In addition,
air must flow over the sensors continuously whenever the unit is in operation.
1.1 Operating Principle
The ISA-44RAL-OD is an all solid-state electronic gas-detecting instrument designed to continuously monitor the
carbon monoxide and oxygen levels in compressed air. The CO sensing element is a gas-sensitive metallic oxide
semiconductor (MOS sensor). A regulator humidifier assembly collects and humidifies a small air sample from the
respiratory air line and passes it over the sensor. If the level of CO in the air passing over the sensor increases to
preset value, the ISA-44RAL-OD alarms with audio (audio alarm) and/or visual (light) signals.
The sensor for the oxygen channel is a micro-fuel cell. It employs a galvanic reaction to emit a steady current. This
current indicates the presence of oxygen to the circuitry. If the oxygen level drops, the current emitted also drops
proportionally. When the current from the cell falls below a predetermined safe level, the alarm circuitry triggers.
The sensing elements of the ISA-44RAL-OD are sensitive to large scale temperature changes. Although this is usually
not a problem with compressed air lines, if the air sample which passes over the sensors is subject to large temperature
changes, the ISA-44RAL-OD may go into false alarms.
The percent oxygen (% oxygen) meter is a linear device. All regions of the meter scale represent approximate
concentrations. It differs from the ppm carbon monoxide (ppm CO) meter, which is not linear.
The ISA-44RAL-OD operates from single-phase 115Vac and/or 12Vdc power and is equipped with relay contacts to
provide additional alarm signals. Operation on single-phase 220 Vac requires several circuitry changes. Contact
ENMET or your distributor for this information.