Secure liquid level detection
May 2017, Level Measurement & Control
Kobold has capacitive level indicators, type NMC, specifically designed to measure liquid levels in tanks. They consist of a measuring probe and a connecting head with a plug-in evaluation module. Depending on the operating conditions, different probes are available:
• NMC-N: Standard version with metal tanks inserted, their walls undertaking the task of a second electrode. It is applicable for fluid foods as well as for different waters.
• NMC-S: The two probe sensor for non-metal tanks for operation in aggressive media.
• NMC-T: Especially for operation in non-metal holding tanks and media of lower conductivity, the designed probe consists of an interior probe and a surrounding pipe of stainless steel serving as a reference electrode.
• NMC-H: The electronics of one stick probe of stainless steel is thermally insulated by a special intermediate piece so that the sensor technology can easily handle up to 125°C.
The measuring system is based on the capacitive measuring method. The measuring probe and the tank wall, or the second electrode form the plates of a capacitor; the medium in the tank is the dielectric fluid. The capacity depends on the medium. The more the medium touches the measuring probe, the higher the capacity. This change is detected by the plug-in evaluation module and transformed in a percentage display or a 4-20 mA signal. As there are no movable parts, the unit operates almost wear-free. Lengths of PTFE coated measuring probes of stainless steel can be freely chosen up to 4000 mm. Problematic apertures at holding tank base or at the side can be avoided by virtue of a simple and secure assembly from top. Fields of application include:
• Water or water-like liquid.
• Liquid food.
• Chemicals and aggressive liquids.
• Pharmaceutical liquids.