LA Series Sensor

The LA202/LA22 true acoustic microphones are very sensitive (60 dB range) and have an absolute calibration, so that the operator can determine where the leak is being produced easily. We offer the air-borne system for all locations where it is possible to do so based on its superior ability to pin-point the location of the leak by comparison of absolute intensity of multiple sensors.

On the reverse of the assembly can be seen a LED acoustic level indicator, push button self test and a calibration adjustment. The LED gives a visible indication of dB level and confirmation following self-test. These functions are thus available both at the sensor and optional PC control system, giving maximum redundancy and options to power station engineers.

The LA series sensor has microphone and all amplifier and filtering electronics in one pre-calibrated assembly. The LA202 show left can be a complete leak detection system; all that is required is a +24 VDC supply. The outputs are both AC acoustic sound and a 4-20mA signal, which is the ABSLOUTE decibel level of filtered sound concentrates on the frequencies of tube leaks.

The normal background noise of a particular sensor will be 70 - 85 dB (the dB will be vary in different areas of the boiler and will be boiler type dependent). Leaks will generate noise of 90 dB and over, and will continue to rise and can be easily distinguished in-between soot-blowing operations.

Detecting a leak is a simple matter of monitoring the sound level of each sensor (which has boiler noise filters applied) and trending the absolute sound level and observing the rate of change against time.

The noise from a steam leak invariably increases with time, while sounds from fans, sprays and mainly soot-blowers vary as they are brought into and out of service.

Sensors are typically placed on both sides of a boiler in a box arrangement at a level in-between two rows of tube banks to allow comparison between absolute sound levels making the location of the leak relatively straight forward.

This is because from the white noise from a steam leak, the high frequencies are attenuated heavily in air, but the sound with frequencies just above the boiler background travel well along the corridors in-between tube banks. The airborne system sensor has a typical listening range up to 45 feet (14 m), with a tube leak (hole) of 0.1 inches (2.5 mm), which can be extended when sound propagates through a tube bank corridor where they are typically located.

The LA series of sensors have the pedigree of 30 years of leak detection design and application experience, originally developed in the 1970s with the old UK CEGB. It was found that when simulating a steam leak at one side of a boiler, the most sensitive transducer for detecting the white noise given off was the airborne sensor developed by our design engineer of the LA series.

• LA Series Sensor