Reed level sensor: Defining the measuring range flexibly

A float-based level sensor with a reed chain is a trusted and comparatively economical solution for continuous level measurement in vessels. Users can define its measuring range flexibly within a given range. This short article describes what should be taken into account.
With a reed-chain level sensor, the guide tube includes a defined amount of reed contacts, with respect to the measuring range. These are combined to form a measuring chain. Report 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 this energy-free level monitoring depends, subsequently, on the distance between your individual contacts: the smaller it is, the more accurate the measurement. Each level sensor in WIKA?s RLT series, for instance, 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. For the reason that there are ?dead bands? at both ends of the tube, i.e. sections that the float will not detect because of design constraints (see graphic).
The graph shows the way 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 could be freely defined. However, it is by no means necessary to utilise the maximum possible measuring range in every applications. The precise adaptation of the number of contacts to the measuring task also has an economic advantage: The reed chain is among the priciest components in an even sensor.
Example ? Dry run monitoring
For dry run monitoring within an oil tank of a compressor, for example, only the lower area of the guide tube is necessary for the measurement. In this case, the upper measuring point of the application form (100 % mark) is defined correspondingly low. It marks the length to the sealing face of the procedure connection. The measuring range is thus defined by the following 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 case, the guide tube can be adapted to along the measuring range.
Note
Further information on the RLT series level sensors are available on the WIKA website. In case you have any questions, your contact will gladly assist you to.
Also read our articles
Level sensors ? the agony of preference
What do dead bands mean with a float switch?
There are also out more about float-based level measurement utilizing a reed chain in the next video:

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