Airborne Acoustic Activity Monitoring
To sense the sound in a boiler, AMI has designed acoustic sensors mounted on the ends of waveguides. The waveguides are mounted on boiler access doors, observation doors, or unused sootblowers ports. The waveguide provides a smooth continuous acoustic path (much like an ear canal) to the sensor and provides thermal protection by eliminating the direct radiant heat of combustion that could overheat the sensor. A secondary purpose of the waveguide is to prevent flyash or wash water from directly contacting the sensor diaphragm. The waveguides are either welded directly to a door or attached with a special fixture and oriented to place the acoustic sensors in as nearly a vertical position as possible.
The sensor is a specially designed pressure transducer for detection of leaks in high pressure and/or high temperature environments on the gas side of furnaces and convection passes of boilers. It is a highly sensitive pressure transducer utilizing piezoelectric crystals with acceleration compensation circuitry to minimize extraneous signals due to mechanical vibrations. Due to the sensor’s operating environment, its mechanical and electrical design was carefully designed to meet the following requirements:
A rigid mechanical construction to avoid mechanical strains on the piezoelectric crystal that could induce unknown changes in sensitivity.
Capability of absorbing very severe thermal shocks (550°F/sec.) without any sensor damage. High sensitivity coupled with extremely high resolution for detection of high frequency noise (leaks).
High degree of reliability in presence of corrosive gas in the boiler environment.