Ultrasonic level detectors

Ultrasonic level transmitters can be used on liquids or solids and can be of the noncontacting or the submerged designs. These errors are from 0.5 to 2% FS over measurement ranges up to 75 m (250 ft) in silos and up to 600 m (2,000 ft) in wells. 

Sonic (up to 9,500 Hz) and ultrasonic (10-70 kHz) level sensors operate either by the absorption (attenuation) of acoustic energy as it travels from source to receiver, or by generating an ultrasonic pulse and measuring the time it takes for the echo to return. If the transmitter is mounted at the top of the tank, the pulse travels in the vapor space above the tank contents, and if it is mounted on the bottom, the time of travel reflects the depth of liquid in the tank. In water, at ambient temperature, the ultrasonic pulse travels at 1,505 m/s (4,936 ft/s). 

Temperature compensation is essential in ultrasonic level measurement, because the velocity of sound is proportional to the square root of tempera- 

Post-Oil Energy Technology After the Age of Fossil Fuels 

Wire-guided float detector installation for high-pressure tanks. 

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In addition to the level-measurement devices illustrated in Figure 7-3, there are air bubbler systems for level detection, ultrasonic level detectors, and radiation level detectors. Ultrasonic and... 

The Pr EN 12668-1 concerns the verification of characteristics of ultrasonic flaw detector. It is mainly applicable to portable equipment incorporating Ascan visualisation on screen, and which bandwidth is comprised between 0,5 and 15 Mhz. The project describes three levels of verification ... 

The prototype of verification system of ultrasonic flaw detector developed is described in the scheme given in figure 2. The verification operators performed with the system are as much automated as possible. The level of automatization is limited by the necessity of human reading of information on flaw detector screen, or other operations as manual adjustment of flaw detector settings. 

Sonic Methods A fixed-point level detector based on sonic-propagation characteristics is available for detection of a liquid-vapor interface. This device uses a piezoelectric transmitter and receiver, separated by a short gap. When the gap is filled with liquid, ultrasonic energy is transmitted across the gap, and the receiver actuates a relay. With a vapor filling the gap, the transmission of ultrasonic energy is insufficient to actuate the receiver. 

With the reference block method the distance law of a model reflector is established experimentally prior to each ultrasonic test. The reference reflectors, mostly bore holes, are drilled into the reference block at different distances, e.g. ASME block. Prior to the test, the reference reflectors are scanned, and their maximised echo amplitudes are marked on the screen of the flaw detector. Finally all amplitude points are connected by a curve. This Distance Amplitude Curve (DAC) serves as the registration level and exactly shows the amplitude-over-distance behaviour" of the reference reflector for the probe in use. Also the individual characteristics of the material are automatically considered. However, this curve may only be applied for defect evaluation, in case the reference block and the test object are made of the same material and have undergone the same heat treatment. As with the DGS-Method, the value of any defect evaluation does not consider the shape and orientation of the defect. The reference block method is safe and easy to apply, and the operator need not to have a deep understanding about the theory of distance laws. 

Acoustic analysis detects changes in the properties of acoustic waves as they travel at ultrasonic frequencies in piezoelectric materials. The interaction between the waves and the phase-matter composition facilitates chemical selectivity and, thus, the detection of CWA s. These are commonly known as surface acoustic wave (SAW) sensors. Reported studies indicate detection limits as low as 0.01 mg m for organophosphorus analytes within a 2 min analysis [1]. There are several commercially available SAW instruments, which can automatically monitor for trace levels of toxic vapors from G-nerve agents and other CWAs, with a high degree of selectivity. A major advantage of SAW detectors is that they can be made small, portable and provide a real-time analysis of unknown samples. One of the drawbacks of these instruments is that sensitivity and a rapid response time are inversely related. In an ideal instrument, both parameters would be obtained without sacrificing one for the other. 

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