5 working principle, 1 gas sensor technology, 2 condition for leak detection – INFICON Sensistor ISH2000P Hydrogen Leak Detector, Panel Model User Manual
Page 14: 3 leak detection modes, Working principle, Gas sensor technology, Condition for leak detection, Leak detection modes, 5working principle
Hydrogen leak detector Sensistor ISH2000
-
Operating Instructions
12
OP-Sensistor ISH2000-EN-201203
EN
5
Working principle
5.1 Gas Sensor Technology
The Sensistor ISH2000 leak detector is using an extremely sensitive hydrogen gas
sensor based on a microelectronic field effect transistor (MOS-FET).
The gas sensitivity appears when hydrogen absorbs into the sensor through a metal
alloy (metal hydride) layer.
Only hydrogen can diffuse into the metal and this makes the sensors practically
insensitive to other substances that do not contain free hydrogen molecules.
The signals from the sensors are processed by a microprocessor which also controls
the sensor temperature with high accuracy, and other sensor diagnostics in order to
ensure perfect functionality. It also automatically compensates for background gas.
5.2 Condition for leak detection
To use the leak detector the test object must be filled and pressurized by tracer gas
(95% N
2
/ 5% H
2
) to get a gas flow through the leak. The tracer gas is a standard
welding gas of industry quality, easy to obtain at low cost. The generic name is
Forming Gas. Appropriate gas filling equipment can be obtained from the leak
detector supplier.
Be careful of how tracer gases are handled after use. Released tracer gas
contaminates the surrounding air with hydrogen and can complicate the following
measurements for a time. Ensure that the tracer gas is ventilated away from the
target area, preferably to the outside of the building.
5.3 Leak detection modes
The detector operates in three modes:
•
The leak locating mode (Detection Mode), mainly used for detecting and locating
leaks but not quantifying them.
•
The hydrogen measurement mode (Analysis Mode) measures the concentration of
hydrogen.
•
The Combined Mode, (default mode) which is a combination of Detection and
Analysis mode.
The Detection Mode operates continuously while the Analysis Mode determines the
hydrogen concentration (and calculates a corresponding leak rate) in a step
measurement. Detection Mode gives no numbers. It therefore needs no actual
calibration. The sensitivity of the sound signal and the moving bar on the display is
set manually or automatically, see below.