Acoustic Flow Monitor

 

The acoustic flow monitor has been developed to provide a reliable method of detecting material flow or flow interruption in pipes and downspouts. It is particularly suited to installations where, due to licensing or administrative restraints, nuclear type detectors are impractical.

 

The acoustic flow monitor consists of two subassemblies: a detector probe that mounts on the downspout and a control unit suitable for wall mounting in a convenient location. The detector probe includes a stainless steel alloy tip that protrudes through the downspout wall into direct contact with the moving material.

 

The control unit includes the required electronics, comparator circuitry, and alarm relay to advise system status. Adjustment and calibration are easily accomplished at the control unit.

 

Operation
As material flows through the downspout, sonic waves are generated at the friction interface between the material and downspout wall, material and sensor probe, and by material particles moving against one another. This sound vibration is transmitted as a physical motion through the tip of the sensor probe. This motion is proportionally converted by a piezoelectric element to an electrical signal, which is forwarded to the control unit. Within the control unit, the signal is amplified and filtered to eliminate non-flow related interference. The incoming signal activates and maintains a "material motion" status. In the event of an empty downspout or one full or partially loaded with non-moving material, the "material motion" signal drops below a set point, providing a contact closure showing pluggage has occurred. An adjustable 10- to 90-second time delay is included in the circuit to prevent nuisance alarms caused by spike vibratory conditions.
 

Application
The acoustic flow monitor should be mounted on the downspout as close to the bunker (or silo) outlet as is physically practical. By doing so, the earliest possible indication of loss of flow is ensured. Should flow stop during normal operation, the alarm signal can be used to automate vibrators, air cannons, or other devices. A second acoustic flow monitor may be located immediately above the feed system and used to trip the feeder if material flow has not been re-established prior to loss of all material within the system. As an alternate, this secondary alarm indication can be provided with a STOCK® Microprocessor Controlled Gravimetric Feeder through a "countdown" circuit within the feeder controls. Optional mounting fixtures and hardware are available upon request.