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 must be taken into account.
With a reed-chain level sensor, the guide tube includes a defined amount of reed contacts, with regards to the measuring range. They are combined to create a measuring chain. The contacts react to the magnetic field of the float, which moves within the guide tube good liquid level.
Accuracy depends on the length between the contacts
The accuracy of this energy-free level monitoring depends, in turn, on the distance between your individual contacts: the smaller 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 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 does not detect due to design constraints (see graphic).
The graph shows the way 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 isn’t a must
The measuring selection of an even sensor therefore lies between your two dead bands specified in the info sheet. Within this range, it is usually 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 probably the priciest 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 area of the guide tube is necessary for the measurement. In this instance, the upper measuring point of the application (100 % mark) is set correspondingly low. It marks the length to the sealing face of the process 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 set beginning with the sealing face. In this instance, the guide tube could be adapted to the length of the measuring range.
Note
Further information on the RLT series level sensors can be found on the WIKA website. Assuming you have any questions, your contact will gladly help you.
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What do dead bands mean with a float switch?
You can also find out more about float-based level measurement using a reed chain in the next video: