Reed level sensor: Defining the measuring range flexibly

A float-based level sensor with a reed chain is really a trusted and comparatively economical solution for continuous level measurement in vessels. Users can define its measuring range flexibly inside a given range. This article describes what has to be taken into account.
With a reed-chain level sensor, the guide tube includes a defined number of reed contacts, according to the measuring range. These are combined to form a measuring chain. The contacts respond to the magnetic field of the float, which moves within the guide tube based on the liquid level.
Accuracy depends on the distance between the contacts
The accuracy of the energy-free level monitoring depends, subsequently, on the distance between the individual contacts: small it really is, the more accurate the measurement. Each level sensor in WIKA?s RLT series, for example, enables measuring ranges with contact distances between 3 and 24 mm. However, a reed chain cannot be stretched across the entire amount of the guide tube. This is because there are ?dead bands? at both ends of the tube, i.e. sections that the float does not detect due to design constraints (see graphic).
The graph shows how the maximum possible measuring range (M) having an air-handling series level sensor is defined: Guide tube length (L) minus dead band (T) and 100 % mark (X).
Maximum measuring range is not a must
The measuring selection of a level sensor therefore lies between the two dead bands specified in the info sheet. In this range, it can be freely defined. However, it is by no means necessary to utilise the utmost possible measuring range in all applications. The exact adaptation of the number of contacts to the measuring task also has an economic advantage: The reed chain is probably the priciest components in an even sensor.
pressure gauge 10 bar ? Dry run monitoring
For dry run monitoring within an oil tank of a compressor, for instance, only the lower the main guide tube is necessary for the measurement. In this instance, the upper measuring point of the application (100 % mark) is defined correspondingly low. It marks the distance to the sealing face of the procedure connection. The measuring range is thus defined by the next equation:
Measuring range length M = guide tube length L ? dead band T ? 100 % mark X
Consequently, the measuring range for detecting a maximum level is determined starting from the sealing face. In this instance, the guide tube can be adapted to along the measuring range.
Note
Further information on the RLT series level sensors can be found on the WIKA website. Should you have any questions, your contact will gladly assist you to.
Also read our articles
Level sensors ? the agony of choice
What do dead bands mean with a float switch?
You can also find out more about float-based level measurement utilizing a reed chain in the following video:

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