2 Description
2.1 General
The MSA Gas Detector Series 47K is designed to continuously monitor the atmosphere for the presence of potentially
explosive gas or vapour in air in the range 0 to 100% LEL.
It is designed for use as an integral part of an MSA fixed gas detection system for the protection of industrial plant and
workers.
• Typical areas where the MSA Series 47K Gas Detector can be used include:
• The chemical and petrochemical industry
• The paint and solvent-processing industry
• The gas-processing industry
• The steel-processing industry
• Municipal areas
• The Production, Warehousing, Distribution, Shipping and processing of gases and vapours
The MSA Series 47K Gas Detector consists of the Series 47K catalytic sensor and the junction box that contains the
terminal board.
There are two versions of the junction box available:
• Flameproof [Ex d] with ¾” NPT cable gland thread
• Increased safety [Ex e] with metric M25 cable gland thread
The following Sensor Versions are available:
• Series 47K-PRP: Poison Resistant Pellistor [100% LEL]
• Series 47K-HT-PRP: High Temperature Poison Resistant Pellistor [100 % UEG]
All versions are available in Stainless Steel 316.
Four accessories are available to allow easy calibration and to adapt the gas detector to various applications:
• Calibration cap
• Flow through adapter
• Duct mount flange
• Weather protection cap with remote calibration capability
2.2 Principle of Operation
The MSA 47K series of sensors operate on the principle of catalytic combustion. The sensing element consists of a pair
of filaments [“pellistors”] connected to a pair of precision resistors to form a Wheatstone bridge.
One of the filaments, the detector, is coated with a catalyst, whilst the other, the compensator is used as a reference to
achieve the best stability.
The gas or vapour diffuses through a porous Stainless Steel sintered disc, which acts as a flashback arrestor. When gas
comes into contact with the surface of the detector filament, it is oxidised. The heat generated by the reaction increases
the temperature of the detector, which results in a change of the detector electrical resistance, and hence an unbalance
of the Wheatstone bridge. The result is an output signal directly proportional to the concentration of the flammable gas or
vapour. The signal is processed by an MSA controller designed to display the gas concentration, actuate alarms and
provide a suitable output signal to activate subordinated external measurement data acquisition systems.
7 Series 47K GB
2 Description
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