INFICON Sensistor ISH2000 Hydrogen Leak Detector - Manual (Page 16)

Hydrogen leak detector Sensistor ISH2000 - Operating Manual
16 OM-Sensistor ISH2000-EN-201304
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 metal-oxide-semiconductor 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 mode
The detector operates in three modes:
•
Locating Mode is mainly used for detecting and locating leaks but not quantifying
them.
• Measuring Mode measures the concentration of hydrogen.
• Combined Mode, (default mode) which is a combination of Locating and Measuring
Mode.
The Locating Mode operates continuously while the Measuring Mode determines
the hydrogen concentration (and calculates a corresponding leak rate) in a step
measurement. Locating 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.
When using the instrument in Measuring Mode, it must be calibrated as described.
See “Calibrate the leak detector” on page 19 in order to give correct figures.