User Manual PolyGard
®
2 Sensors 2023-11 Page 9 | 40
D: Infrared Sensor Element for Methane, Propane, Carbon Dioxide and R32
The integrated sensor is based on the principle of the infrared absorption of gases and achieves the
highest requirements concerning accuracy and reliability. The sensor technology uses the individual
absorption spectrum of the atomic bonds of the gas to be monitored and determines the exact con-
centration present through its precise quantitative analysis. Cross-sensitivity to other gases is virtu-
ally eliminated by the infrared measuring principle. The evaluation electronics reliably compensate
for all external drift and temperature influences thanks to the dual-beam technology, various envi-
ronmental sensors and the integrated software. Due to the measuring principle and the high-quality
processing, IR sensors require very little maintenance, but MSR recommends regular calibration of
the sensors, depending on the application.
E: MPS™ Sensor Element
The sensor consists of several complementary chemical sensors integrated on a single chip. This
system is called "Molecular Property Spectrometer", or MPS
TM
for short.
The core of the MPS
TM
sensor is a patented transducer in the form of a so-called "hot plate" with
embedded "Joule heater" and resistance thermometer. The hot plate converts electrical energy into
heat and light energy. When a voltage is applied to the spiral-shaped resistance heater (Joule heater),
electric current (electrons) flows into the hot plate. The resistance of the heating metal to this current
flow generates light (photons) and heat (free electrons and phonons).
The presence of combustible gas causes changes in the thermodynamic properties of the surround-
ing air/gas mixture, which are measured by the sensor. From the multitude of thermodynamic and
electrostatic molecular properties of the substance present in the environment, it forms a compre-
hensive data set of chemical information in less than a second. The raw data from the sensor is pro-
cessed by special algorithms in the sensor's software to make accurate statements about the de-
tected gas. One aspect is the classification of gases by the density and molecular weight of the sub-
stance. Based on the thermal mass measurement of the air surrounding the hot plate, the algorithm
can identify the types of molecules in the ambient air and determine the exact concentration.
During the start-up process, the sensor carries out an initialisation process. During this process, it
records a wide variety of data from the environment. Through the collected data sets, the sensor is
perfectly adjusted to the application and compensated against all changes in the environmental con-
ditions.
The following applies to all sensor elements:
Certain substances and gases in the ambient air to be monitored can affect the sensitivity of the
sensor element or destroy it completely. This is called poisoning.
The following sensor poisons are currently known:
• Polymerising substances, such as acrylonitrile, styrene and silicone.
• Corrosive substances, such as ammonia, nitrogen dioxide or halogenated hydrocarbons.
• Catalytic poisons, such as compounds of sulphur, phosphor or silicon.
• Organic solvents
• Oils and lubricants
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