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Vibrating Rod Level Switches
Operating Principle

Solitel® operates on the principle of detecting the dampening effect when solids are brought into contact with the vibrating rod. This principle is illustrated in the drawing at right.

Normally, SOLITEL vibrates at a frequency of approximately 350 Hz. This vibration is created by exciting the transmit piezoelectric crystal attached at the base of the outer rod. The piezoelectric crystal converts electrical energy to mechanical (vibratory) energy. Both the inner and outer rods have the same natural frequency (the frequency at which a body will vibrate freely).

The vibratory energy from the outer rod is transmitted to the inner rod, setting it into vibration, and establishing resonance vibration between the rods. (This is similar to the operation of a musical tuning fork where both prongs of the fork have the same natural frequency, and a mechanical force to one prong produces resonance vibration between them.)

The vibration, detected by the receive piezoelectric crystal, is converted to low level electrical energy. The electronics receive the low voltage signal from the receive crystal and amplify it. The amplified signal is compared to the set point in the comparator circuit which determines relay operation. The signal is then filtered to remove unwanted frequency; it is amplified and sent to the transmit crystal to create the vibration.

In free space, the inner and outer rods vibrate at their natural frequency. When solids come into contact with the outer rod, the vibration is dampened, decreasing the electrical signal, providing relay actuation.

When the electrical signal from the receive crystal decreases, the electronics immediately begins a self-cleaning cycle which takes approximately three to eight seconds, depending upon the sensitivity adjustment. The amplitude is increased, attempting to dislodge loose solids that may have accumulated on the probe. Upon successful self-cleaning, the signal from the receive crystal increases and the probe returns to normal operation. However, if vibration does not resume, then actual contact of the solids has been made and the alarm is indicated.


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