Ultrasonic Level Switch | Working Principle & Applications

Ultrasonic Level Switch | Ultrasonic gap switch

An ultrasonic level switch is a device that detects the presence or absence of a liquid at a specific spot using inaudible high-frequency sound (ultrasound). Ultrasonic level switch also known bt the name of Ultrasonic gap switch. A sensor and an electrical control unit make up the apparatus. Ultrasonic level switches measure the level of a liquid by using the characteristics of sound transmission in vapour and liquids. The signal intensity of sound is greatly diminished as it travels through the air. Sound maintains almost all of its signal intensity when it moves through liquid. We must decide whether there is a liquid or a gas (air) in the gap in order to detect liquid level. Since liquids have a higher density than gases, sound can travel through them more easily. The sensor gap has two sides: one side transmits sound, the other side picks it up. A significant amount of sound is picked up at the detection side when liquid is present. There is a faint sound heard when gas (air) is present. The electronics recognise this variation and switch a relay appropriately.



ultra sonic level switch

Construction of Ultrasonic Level Switch

Two piezoelectric crystals are found in ultrasonic switch sensors; one transmits sound and the other receives sound. Each crystal is attached to the inside of a gap in the metal sensor on that side. High frequency sound (1 to 3 MHz) produced by the transmit crystal is transmitted to the receiver crystal by way of the gap. The electronics process the electric signal created when the receiver crystal turns the sound energy into a signal to determine whether the gap is filled with liquid or air.

ultrasonic level switch working

Working Principle of Ultrasonic level switch | ultrasonic level switch operating principle

Transmission of ultrasonic sound waves via air results in significant attenuation. On the other hand, when liquid is present, sound waves are transmitted far more effectively. Electrical signals produced by the electronic control unit are transformed at the sensor into ultrasonic energy bursts. The liquid sensing gap is used to transmit the ultrasonic bursts. The solid-state electronics provide a data enable condition after receiving a valid signal, indicating the presence of liquid. A relay is activated by this signal, and an output condition is produced.

At the tip of the transducer, two piezoelectric crystals are used in ultrasonic switches, which are then sealed in epoxy. When a voltage is supplied, the crystals’ ceramic substance vibrates at a specific frequency. The “transmitting crystal” transforms the voltage into an ultrasonic signal when it is delivered from the electronics to one of the two crystals.

The second crystal, known as the “receiving crystal,” senses the ultrasonic signal and transforms it back into an electronic signal due to the liquid that fills the transducer gap. Liquid is present in the transducer gap, according to the signal, which is delivered to the electronics. The ultrasonic signal is weakened and ineffective for the receiving crystal to detect if there is no liquid present.

In order to detect the presence of liquid, the ultrasonic transducer continuously scans the gap. When employed as a high-level switch, if an electrical device senses a wet gap, it will immediately actuate a relay. The same is true when it is employed as a low-level switch; it constantly checks the gap for a dry condition.

Ultrasonic Level Switch application and Limitations

There is no need for calibration or setup when using ultrasonic level switches in a wide range of applications. The kinds of processes they can work in, though, are constrained. Before choosing an ultrasonic level switch for your application, you must take into account the following criteria.

Only liquids are allowed to be used as process media. It is impossible for the ultrasonic level switch to distinguish between two gases or between a gas and a solid. For accurate detection, a liquid’s density must be uniform.

Pure liquids only; a liquid with a significant solids content won’t be able to transmit sound well enough to enable for detection. The maximum permitted level is typically 5% suspended solids.

The liquid must flow; else, false alarms will result from applications where the liquid cannot drain out of the sensor gap. The device won’t work properly if a liquid is too viscous to pass through a 3/4″ gap. Different mounting techniques can sometimes resolve this issue, but some liquids are simply too viscous.

No (or few) bubbles, especially when dealing with more viscous fluids. The sound signal won’t be able to get across the gap if there are large bubbles in thick fluids. Due to their tendency to be very small, bubbles in low viscosity fluids can be found in quite high quantities (Alka-Seltzer in water). The ultrasonic level switches will operate without error if these instructions are properly followed, eliminating the need for periodic calibration or adjustments.

Manufacturer wise Ultrasonic level switch

There are many companies who manufacture ultrasonic gap switch. some of them are below

  • magnetrol ultrasonic level switch
  • rosemount ultrasonic level switch
  • sor ultrasonic level switch
  • ultrasonic level switch endress hauser
  • flowline ultrasonic level switch
  • mobrey ultrasonic level switch
  • ultrasonic level switch siemens
  • abb ultrasonic level switch
  • drexelbrook ultrasonic level switch
  • dwyer ultrasonic level switch etc.

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