Vibrating tuning fork devices for monitoring liquid level and activating switch contacts at predetermined liquid level thresholds.
A vibrating tuning fork liquid level switch is an instrument for monitoring the height of a liquid and tripping a relay contact switch or transmitting a solid state relay switch output when a maximum, minimum or intermediate level has been reached. The liquid level switch output can then be utilised by other instrumentation to open a valve, illuminate a warning lamp, activate an audible alarm, or switch on a pump.
Vibrating tuning fork liquid level switches are threshold contact trip devices which typically consist of a tuning fork which extends out from the switch housing.
In operation a piezoelectric oscillator is used to vibrate the tuning fork at its natural frequency for air.
A second piezoelectric device is used to pick-up the frequency of the vibrating tuning fork. When the liquid level rises and covers the tuning fork it will vibrate at a lower frequency.
This change in vibration frequency is used to detect when the required liquid level has been reached.
A vibrating tuning fork liquid level switch makes direct contact with the liquid to be measured, and therefore material compatibility has to be a consideration.
Since there are no pressure sensitive components exposed to the inside of the tank it is possible to fit tuning fork level switches to sealed pressurised tanks.
Also, since there is no sensitive components immersed in the fluid it is possible to use them on higher temperature media that would not be tolerated by other types of liquid level switch.
Vibrating tuning fork liquid level switches are generally mounted through the top or side of the tank with the tuning fork protruding horizontally into the tank.
- Not affected by any surface disturbances such turbulence, foaming, vibration
- High temperature fluid compatibility since no sensitive components make contact with the fluid
- Small compact size
- Sealed pressurised or evacuated vessels will not affect performance
- Thick or sticky media will leave a coating on the probe which will affect vibration frequency
- Fouling can interfere with resonant frequency causing false switch activation
- Tuning fork protruding into liquid causing obstruction, attracting fouling and hygienic cleanliness issues
- High cost