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 inside a given range. This article describes what has to be taken into account.
With a reed-chain level sensor, the guide tube contains a defined number of reed contacts, based on the measuring range. They are combined to form a measuring chain. The contacts react to the magnetic field of the float, which moves within the guide tube in line with 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 your individual contacts: the smaller it really is, the more accurate the measurement. Each level sensor in WIKA?s Little-known , for example, enables measuring ranges with contact distances between 3 and 24 mm. However, a reed chain cannot be stretched along the entire amount of the guide tube. This is due to 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).
Aggravate 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 isn’t a must
The measuring selection of a level sensor therefore lies between the two dead bands specified in the data sheet. In this range, it can be freely defined. However, it really is by no means essential to utilise the maximum possible measuring range in all applications. The precise adaptation of the amount of contacts to the measuring task also has an economic advantage: The reed chain is probably the most expensive components in a level sensor.
Example ? Dry run monitoring
For dry run monitoring in an oil tank of a compressor, for instance, only the lower the main guide tube is necessary for the measurement. In this instance, top of the measuring point of the application (100 % mark) is defined correspondingly low. It marks the length to the sealing face of the process 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 set beginning with the sealing face. In Hell , the guide tube could be adapted to the length of the measuring range.
Note
More info on the RLT series level sensors can be found on the WIKA website. For those who have any questions, your contact will gladly assist you to.
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There are also out more about float-based level measurement utilizing a reed chain in the following video: