Ultrasonicgasleakdetectiontechnology

The ultrasonic (acoustic) gas leak detection technology works by listening for ultrasound emitted from pressurised gas leaks.

Instead of measuring a concentration level in LEL as traditional gas detectors (point and open path detectors) the ultrasonic gas leak detectors raise an instant on/off alarm if a leak is detected. The ultrasonic gas leak detectors do not have to wait until the gas concentration has accumulated to a potentially dangerous gas cloud, they react instantaneously. This means that unlike traditional gas detectors, ultrasonic detectors can detect gas leaks at the speed of sound without being affected by wind directions or gas dilution.

Instead of measuring a concentration level in LEL, the ultrasonic (acoustic) gas leak detection method is based on the so-called leak rate. This makes detection more reliable and efficient as it is possible to verify the performance of the detection system.

Using the industry standard for small leaks 0.1 kg/s as the standard for leaks to be detected, the detection coverage of an ultrasonic (acoustic) gas leak detector can be determined and verified during commissioning.

Theoryofultrasound

When gas moves from a high-pressure area to a low-pressure area through a hole , it expands very rapidly and produces a turbulent flow, resulting in an audible "hissing" sound. The "hissing" sound is broadband acoustic sound, which ranges from the audible frequency range (20 Hz to 20 kHz) into the ultrasonic frequency range (16 kHz to 10 MHz).

The level of ultrasound produced by a gas leak is determined by three main factors (mainly 1 and 2):

The pressure drop across the leak
The physical size of the leak
Gas specific properties such as: molecule weight and the specific heat ratio of the gas

For the turbulent flow to take place and produce ultrasound the pressure on one side of the leak has to be at least twice the pressure of the other side of the leak. Besides, if the hole is too big, the pressure drop across the hole will be too little, and no ultrasound will be produced.

The three factors above - mainly the pressure and the leak size - will decide whether enough ultrasound is generated to trigger an ultrasonic (acoustic) gas leak detector. The standard for these parameters is referred to as the leak rate - and this standard can be calculated by means of a mass flow formula.