MSA 47K Series User Manual

GB
MSA DESCRIPTION
Series 47K Gas Detector [SIL 2] 9
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.
2.3. Technical Specification
The Series 47K combustible gas sensors are designed to meet the rigorous
requirements of ATEX Directive 2014/34/EU for fixed gas detection installations.
Sensor
Power consumption 1 Watt, typically
Linear dynamic range Standard & PRP & HT-Sensor: 0–100% LEL
Response time t
50
≤10 sec for propane + methane
t
90
≤20 sec for propane + methane
For other gases or vapours the response time
may be longer.
Typical sensitivity PRP- sensor methane: 12 mV/vol%;
propane: 16 mV/vol%;
HT-PRP- sensor methane: 12 mV/vol%;
propane: 16 mV/vol%;
Operating configuration Wheatstone Bridge circuit
Operating mode Constant current
Sensor current 310 mA for 47K-PRP,
280 mA for 47K-HT-PRP
V
max
10 V
Operating life time 3 Years, in clean air, typically
Storage life time 5 Years, in MSA container, typically
Storage temperature range -20 °C to +40 °C**

MSA 47K Series Specifications

General

Brand	MSA
Model	47K Series
Category	Gas Detectors
Language	English