Primary Areas of Application
Where material to be sensed constantly changes physical properties, eg: Municipal Solid Waste. Reliable sensing does not depend on any specific physical or electrical characteristics of the material.
Eg: Textile fibers, onion skins, popcorn, Styrofoam pellets, puffed cereals. This sensing technique permits sensing products which are so light that they cannot be reliably sensed by other means. Reliably senses products with bulk densities of less than 1/4 lb./cubic foot.
Stringy, fibrous materials
Eg: Yarn, chipped fibers, waste paper, trash. Sensor is mounted flush with bin wall to prevent material build-up at sensing point. No moving parts to catch fibers.
Eg: Puffed cereals, potato chips. Nothing projects into falling product to crush it, no motion of sensor to fracture fragile products.
Principle of Operation
A pair of matched sensors is connected to an amplifier as a receiver (microphone) and a transmitter (loudspeaker). When the amplifier gain is increased to the point where its gain exceeds the loss in the acoustic path between the sensors, oscillation (feedback) occurs. An object entering the acoustic path increases the loss and the oscillation decreases.
In the Sonac© system, one sensor is connected to the Sonac© amplifier and operates essentially as a loudspeaker. This transmitting sensor will produce ultrasonic sound waves of the frequency dictated by the sensors themselves. The other sensor which we will call the receiving sensor is connected to the amplifier as a microphone and will deliver to the amplifier electrical energy from ultrasonic sounds reaching its diaphragm. The amplifier itself is capable of amplifying the weak sounds received by the receiving sensor more than 1,000,000 times.
The Sonac© sensors are, by design, quite directional in their response to sound waves. If the transmitting and receiving sensors are positioned facing each other and the path between the two sensors is unobstructed and the electrical gain in the amplifier is sufficient to overcome the losses in sound energy across the path between the two sensors, acoustic feedback will occur. This, of course, cannot be heard, as Sonac© is designed to operate near 38,000 Hz. This is well above the range of human hearing.
When the acoustic characteristics of the air path are changed by variations in temperature, relative humidity, or standing wave conditions, then the Sonac© system merely adjusts itself to some new frequency which is optimum for the present path conditions. In every case the actual frequency of the acoustic feedback in the Sonac© path is whatever frequency will produce the least loss across the path. In actual operation, this change in frequency is limited by the electrical characteristics of the amplifier and the acoustic properties of the sensors.
Single Point Switch for on-off control of bulk solids. On-off switch presence/absence, indication of objects