■ Summary of Ultrasonic Wave

Ultrasonic Wave is wave energy like light or an electric wave but its traveling speed is comparatively slow, and due to its specific character that it’s reflected easily against a medium that shows different should impedance, it’s normally used by a telemeter and diagnostic device, etc. However, beside such character of the ultrasonic wave, by utilizing its another character that when ultrasonic wave passes through a medium it causes reduce of signal, disguised changes to occur or time difference, it’s been applied with the industrial field for being used for producing various measurement devices for measuring density, viscosity and flow, etc. and its usage is being expended increasingly due to the development of signal processing technology.

In addition, ultrasonic wave sensor is widely used for quality control and factory management purposes from the fields of still industry, shipbuilding, heavy industry, aviation, ceramic and semi-conductor industry, etc., it’s also utilized for a nuclear or thermal power plant, bridge, and for diagnosing the safety of the large structure of a military facility, for military use-underwater sonar, liquid flow measurement device for water supply or for oil pipeline in addition to a fish finder.

■ Understanding of Ultrasonic Wave Measurement Device

An ultrasonic wave liquid level monitor, having merits of high accuracy while its operation and maintenance can be performed easily compared to that of a mechanical level instrument, measures the distance from an object reflecting the ultrasonic waves by means of using a pulse reflection method of ultrasonic waves prevails in air.
Use the lower frequency when the distance that is able to be measured becomes more distant, and with transmitting several tense of KHZ bends of ultrasonic pulse signals and by measuring the length of time from the transmission to reception of the ultrasonic wave, it displays the distance calculated. And also because the sound velocity in the atmosphere changes depending on temperature, having a temperature compensation is necessarily required.
The signal received is greatly affected by the angle of the sensor and the object reflecting it, it’s necessary that the surface of a subject article and that of the sensor should be kept in parallel when installing them. In particular, when it is applied to the progress where powders, etc. are being deposited, the sensor should be installed in consideration of a measuring angle of the deposit so that the receiving signal can be sufficiently accommodated. Also, it’s necessary to take a precaution for installing a sensor that the measurement device has a malfunction due to the frequency property of a pulse signal contained in noises when the noise of a surrounding area is high.

Principle of Level Measurement

The transducer (Sensor) measures the length of time from the transmission to reception of the ultrasonic signal (pulse), reflected from an object that was transmitted from the sensor, thereby it calculates the distance and level between the sensor and the object its distance or level to be measured.

◎ Distance [m] = {Pulse Delay Time x the Velocity of Sound} /2
◎ The velocity of Sound in Air [m/sec] = 331.5 + 0.6 x Temperature [℃]