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 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, depending on the measuring range. They 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, in turn, 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 can’t be stretched across the entire length of the guide tube. The reason being you can find ?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 how the maximum possible measuring range (M) with 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 range of an even sensor therefore lies between your two dead bands specified in the info sheet. In this range, it really is freely defined. However, it really is by no means necessary to utilise the maximum possible measuring range in every applications. The precise adaptation of the amount of contacts to the measuring task also offers an economic advantage: The reed chain is among the most expensive components in a level sensor.
Example ? Dry run monitoring
For dry run monitoring within an oil tank of a compressor, for instance, only the lower part of the guide tube is necessary for the measurement. In this case, top of the measuring point of the application form (100 % mark) is set correspondingly low. It marks the distance 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 beginning with the sealing face. In cases like this, the guide tube could be adapted to the length of the measuring range.
Note
Condemning on the RLT series level sensors can be found 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?
You can also find out more about float-based level measurement utilizing a reed chain in the next video:g

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