Level switches are point level measurement instruments used to mark a single, preset level condition such as high or low level condition that would trigger an alarm or switch.
Level Switch Technology:
Capacitive
Capacitance level instruments operate on the electrical characteristics of a capacitor. A capacitor is made of two conductive plates isolated from one another by a dielectric. Capable of
storing an electrical charge, that charge varies depending upon the conductivity of the dielectric.
In level applications, the medium to be measured serves the dielectric while the tank wall and sensor are the conductive plates. As the tank fills the sensor probe is exposed to a more
conductive material than air and the capacitance value of the probe increases. This value is converted to an output signal that can be used to display the level or activate a switch or control.
Capacitance level instruments do not work well with low capacitance materials like plastic, sand, etc. or with materials having a large particle size (and thus a lot of air pockets). Material
build-up along the probe can also make readings inaccurate.
Conductive
Conductivity level sensors use a low-voltage, current-limited power source applied across separate electrodes to detect the medium's resistance when their electrodes are covered by the process
material. Normally used with water, wastewater, water-based liquids; conductive level probes are simple to install and use. They have the added benefit of being solid state.
Conductivity level sensors provide point level detection and are adept at switching functions for minimum, maximum or differential applications. If buildup insulates the probe from the medium,
it will stop working properly.
Float
Float level instruments are mechanical devices that move in conjunction with the level of the liquid medium. The movement of the float indicates the level and can actuate a switch or create an
output signal. Float level instruments are an economical and practical solution.
Optical
Optical level instruments contains an infrared LED and a light receiver. Light from the LED is directed into a prism which forms the tip of the sensor. With no liquid present, light from the LED
is reflected within the prism to the receiver. When rising liquid immerses the prism, the light is refracted out into the liquid, leaving little or no light to reach the receiver. Sensing this
change, the receiver actuates electronic switching within the unit to operate an external alarm or control circuit.
Ultrasonic
Ultrasonic level instruments use sound waves to determine the level of liquids, solids, and slurries. Consisting of two elements, a high efficiency transducer and an electronic transceiver,
these non-contact systems measure the time for an ultrasonic pulse and reflected echo make a complete round trip between the transducer and the sensed material level. Ultrasonic systems can
also measure open channel flow, volumetric output, and differential level.
While highly accurate, ultrasonic level instruments must compensate for temperature. Applications involving heavy dust, foam or surface turbulence are not advised as the ultrasonic pulse can be
absorbed or otherwise distorted affecting accuracy.
Vibrating Fork
Vibrating fork level instruments are designed to vibrate at its frequency by a pair of piezoceramic discs. When the forks come in contact with the medium the frequency and amplitude changes.
That change is detected and converted into a switch signal. Tuning forks are particularly good for high viscosity materials. Models with high excitation frequency ensure interference free
applications in turbulent surfaces.
If you have any questions regarding level instruments please don't hesitate to speak with one of our engineers by e-mailing us at sales@instrumart.com or calling 1-800-884-4967.
