Hysteresis of Fork Liquid Level Switches in Specific Applications

In Fork Liquid Level Switches, piezoelectric devices are utilized to achieve vibration drive and detection. Once resonant vibrating forks contact with measured medium, vibration frequency of forks substantially decreases, and the output signal from piezoelectric detection device decreases accordingly. Then an integrated circuit is designed to analyze the signal from piezoelectric device and output a switch signal as a result. The hysteretic effect of Fork Liquid Level Switch is highly related to measurement accuracy.

Hysteresis is an important static index in sensors. Hysteresis refers to the phenomenon that when showing the relationship between the quantity of state and the variables of state in the substance obtained by test bed, it can be seen to draw a loop phenomenon which the quantity of state is not consistent at the time of increasing and decreasing after the variable of state was increased or decreased cyclically in a predetermined range.

For Fork Liquid Level Switches, due to its functional characteristics, hysteresis refers to that when the fork liquid level switch is vertically installed, the position when the level rises to the switching-point the tines is marked as X1, and the position when the level falls to the switching-point of the tines is marked as X2. The distance between X1 and X2 is the hysteresis of the fork liquid level switch. As shown in the figure, the horizontal axis X is the load and the vertical axis Y is the sensitivity output.

Jiwei fully considers the hysteresis of the Fork Liquid Level Switches, to  optimize the hysteresis, different algorithms are used for calculation according to the density of different media, and finally the calibration is carried out according to the experimental results.

For example, in the measurement of slurry at the desulfurization tower of coal chemical industry, the slurry is highly alkaline, fluctuating and viscous. When measuring the fluctuating and viscous liquid level, it is inevitable to cause a false alarm of Fork Liquid Level Switches.

To improve the measurement reliability, Jiwei R&D engineers take reasonable delay time in the circuit according to the characteristics of viscous fluctuating slurry, to achieve the most optimal hysteresis. These designs can effectively avoid the false alarm of the Fork Liquid Level Switches and guarantee the measurement accuracy. At the same time, it is recommended to install the instrument in a vertical position and away from the inlet or outlet. In the case with mixing equipments, the installation positions of Fork Liquid Level Switches should be as far away from the mixing area as possible.