Magnetic Immersion Probes

Measurement Principle

Magnet-operated immersion probes are used in clean liquids, such as solvents or oils. The float, guided by a probe tube, floats on the liquid surface. By means of its magnetic field, the ring magnet built into the float activates the reed contacts installed in the guide pipe. These are switched when the float is located in the appropriate position. The reed contacts are designed as normally closed, normally open or change-over contact switches. The measurement is independent of the electrical properties of the liquid, pressure, temperature and density.

Operation Mode

Limit value magnet-operated immersion probes are designed for use in clean fluids, such as water, solvents, oils and fuels. Versions are available depending on the fluids:

• Plastic for aggressive acids and lyes
• Stainless steel for water, oils etc
• Stainless steel in Ex version for flammable fluids such as fuels, solvents, alcohols

To give the reed contact a dual-stable switching characteristic, the magnet-operated immersion probe with 3 contacts has 2 floats and corresponding adjustment rings.

Measuring Principle

A float moves along a vertical guide tube. The permanent magnet fixed in the float switches the contacts of a reed contact resistor chain. This resistor chain acts as a voltage divider and provides the voltage values corresponding to the medium level. The resolution is dependent on the number of contacts used. The measurement is independent of the electrical properties of the filling material, as well as the pressure, temperature and density.

Operation Mode

The permanent magnet located inside the float actuates the reed switches inside the guide tube. When actuated, these reed switches switch between a series of resistors in the guide tube, thus changing the total resistance nearly continuously, depending on the resolution. In addition to the 3-wire potentiometer circuit, 4 mA…20 mA and 2-wire PLM signals are also available as electrical outputs.