Functionality and technology of level sensors

A level sensor determines the level of fluids or other substances that flow in an open or closed system. The two main level sensor types are continuous level sensors that accurately measure levels to a specific limit and point level sensors that simply determine whether the liquid level is high or low. In this article, sensor experts Baumer explain the functionality and technology behind their complete range of precision level measuring instruments.

Level sensor types

Expert liquid level sensor manufacturer Baumer offers a variety of continuous level sensor types that provide fast response times and precise measurements. Famed for their easy configuration and cost-efficient integration, Baumer level measuring instruments ensure process stability and smooth operation. Available with a wide selection of process connections and clever adapter systems, Baumer level sensors minimise risk even in demanding environments.

Level switches (Frequency sweep technology)

Baumer’s CleverLevel level switch uses frequency sweep technology to deliver easy and universal point level detection for all media. An electrode in the tip of the sensor combines with the process environment to form a capacitor and, depending on its DC value, the medium determines the capacity value. Along with a coil in the sensor electronics, this creates a resonance circuit that triggers a switching signal in accordance with programmable trigger thresholds.

Hydrostatic pressure sensors (Hydrostatic level measurement)

Roughly half of all level measurements in tanks are performed using pressure sensors, like Baumer’s innovative CombiPress . The density of the medium must be known and calibrated for accurate level detection. Unpressurised tanks can suffice with a single relative pressure sensor on or near the tank bottom, while pressurised tanks generally need a second pressure sensor to calculate head pressure in the tank.

Floatless level sensors (Potentiometric level measurement)

A potentiometer, like Baumer’s LSP floatless level sensor, uses the ratiometric operating principle, whereby an output signal changes in proportion to a change in the input or supply voltage. The level sensor features a low-resistance measuring tube that is immersed in an electrically conductive liquid. A higher frequency current is run through the measuring tube and the voltage between the probe and the tank wall is sent to an amplifier. In homogeneous medium conditions, this will be proportional to the level.

Ultrasonic level sensors (Ultrasonic level measurement)

Baumer supplies an extensive range of ultrasonic level sensor types that use the measured propagation time of an ultrasonic signal. These high-tech level sensors essentially transmit high-frequency sound waves that are reflected on the surface of the medium (liquid or powder). With ultrasonic sensors for continuous level measurement, the measured distance value from the sensor to the media surface is given as a voltage value and the output current or voltage is proportional to the level or distance of the media surface.

Capacitive level switches (Capacitive level measurement)

Capacitive sensors, like Baumer’s contact and non-contact level measuring instruments, operate like an open condenser. An electrical field forms between the measuring electrode and GND electrode. Materials with a dielectric constant greater than air enter the electrical field and the capacity of the field increases depending on the dielectric constant of this material. In turn, the sensor’s electronics measure this capacity increase and the resulting signal is conditioned through signal processing and causes output switching at a corresponding magnitude.

Optical level switches (Photoelectric level measurement)

Baumer boasts an extensive selection of optical level sensor types that operate based on the alteration of the critical angle for total internal reflection, depending on whether the sensor tip is surrounded by liquid or air. If the sensor tip is surrounded by a liquid (which may be electrically conductive, turbid or clear), then the light beam is deflected into the liquid and the sensor output changes its switching status. The same principle is used in leakage sensors.

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