Technology: Potentiometric Level Measurement
Martin DümlingMany measurement technologies quickly capitulate when expected to deal with liquids which are highly adhesive or heavily contaminated or which generate
a lot of foam; this is precisely where potentiometric measurement technology demonstrates its full strength. Potentiometric level sensors are ideal for measuring levels in mobile wastewater containers, during the manufacture
of cosmetic creams or in ceramic slips.
Potentiometric measurement technology takes advantage of the conductivity of liquids. Consequently, the use of this technology is limited to liquids with a minimum conductivity of 1 µS/cm.
Potentiometric level sensors are an outstanding alternative to capacitive measurement technology and to probes based on the principle of guided microwaves in watery liquids.
Essentially, potentiometric measurement technology involves directing a current through a low-resistance probe tube and measuring the voltage at the upper and lower ends of the probe tube. The liquid, which is grounded via the tank, turns the probe tube into a potentiometer and the ratio between the two voltages changes according to the level of the liquid. The ratio of the two voltages is proportional to the level.
Simply put, the system of probe and liquid can be regarded as a potentiometer, whereby a change in the level corresponds to the turning on a normal potentiometer.
The dependency of the measurement value on the specific resistance of the liquid is for all practical purposes negligible as long as the electrical resistance of the liquid is much higher than that of the probe tube.
Technology: Magnetostrictive Filling Level Measurement
Martin DümlingMagnetostrictive filling level measurement is a float-based technology enabling determination of the filling level to an accuracy within 0.3 mm. The measurement is unaffected by changes in the physical-chemical conditions of the media such as frothing, conductivity, dielectric constant, pressure, temperature, vapours, condensation, precipitation and blistering. No adjustment of the measuring probe to specific liquids is necessary, eliminating additional expenses for recalibration or adaptation whenever the liquid changes. When magnetostrictive filling level measurement is used, both the separation layers and the overall filling level can easily be measured with the aid of a second float. Separation layer measurement is not affected by emulsion formation at the separation layer. Magnetostrictive filling level measurement is not only more cost-effective than a TDR probe (guided microwave), but is also as a rule easier to install and completely maintenance-free.
The history of magnetostrictive filling level measurement started in 1842 when James Joule discovered that some materials deform under the influence of a magnetic field. This effect became known as the magnetostrictive effect. But it was not until a century later that the effect was used for commercial position determination. The measuring principle was initially used in engineering for tool carriage position determination and is still used for this purpose even today owing to its reliability, accuracy and response rate. Moreover, the position of the lift is often determined by means of a magnetostrictive position transducer as the required sensor lengths can be built without problems But engineering is not the only application to benefit from the technological strengths of magnetostrictive position determination; filling level technology is enhanced as well because of its reliability and accuracy.