Ultrasonic Temperature Transducer:

Ultrasonic Temperature Transducer (sound vibrations above 20 kHz) are useful when we are concerned with rapid temperature fluctuations, temperature extremes, limited access, nuclear or other severe environmental requirements and measurement of temperature distribution inside solid bodies.

They may be used to measure the distribution of parameters other than temperature (example flow). Ultrasonics also offers possibilities of remote sensing.

Ultrasonic thermometer sensors permit one to measure an extremely wide range of temperatures, from cryogenic to plasma levels and to achieve micro to milli-second response time, milli-degree resolution, greater choice of materials for sensors, operation in nuclear or corrosive environment and remote location of transducer.

Using Ultrasonic Temperature Transducer for profiling permits one to obtain 2 — 10 or more temperatures using a single transmission line. This feature simplifies installa­tion and provides reliable, accurate data at a reasonable price.

Frequency Generating Transducer

Unlike variable parameter analog transducers, frequency and pulse generating transducers measure physical variables in terms of a pulse repetition rate.

Since frequency is an analog quantity, these can be treated as either analog or digital devices. Therefore, any phenomenon to be measured is converted into a corresponding rate of pulse generation which undergoes counting process and is made digital in nature.

These transducers produce a simple series of voltage or current pulses or cycles in proportion to the change in the physical parameter being measured. The series of pulses can be counted over a certain precisely determined period of time and the input magnitude can be known with considerable accuracy.

Examples of such devices are pulse generating pick ups operating on the variable reluctance principle, photo-tubes, etc.

Reluctance Pulse Pick up

This transducer is very suitable for the measurement of shaft speed and liquid flow. It is based on the principle that if the field of any magnet is varied

momentarily by the motion of an external magnetic body near it, a voltage pulse is generated at the coil of the magnet because of the change in flux surrounding the coil. The transducer consists of a permanent magnet on which a coil is wound. The output voltage depends upon the rate of change of magnetic flux and the number of turns. Flux depends upon the clearance between the pick up and the actuating medium, the rate of movement and size of the actuating medium. The output voltage is inversely proportional to the distance between the head of the pick up and the actuating medium.

The pick up is actuated by the teeth of a gear or blades of turbines. In rpm measurement, the pick up is placed near the teeth of a gear. The motion of the gear tooth distorts the magnetic field around the core magnet.

A voltage pulse is produced every time a tooth enters or leaves the area of the pick up coil. The frequency of pulse is then proportional to the speed of the gear. This can be used for a tachometer.

Similarly, a pick up can be used to determine the flow, as the speed of the turbine through which the liquid flows is proportional to the flow. The total pulses counted are proportional to the total flow.