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 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 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, subsequently, on the distance between the 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 amount of the guide tube. The reason being 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) 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 range of a level sensor therefore lies between your two dead bands specified in the data sheet. Within this range, it really is freely defined. However, it is by no means essential to utilise the utmost 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 most expensive components in an even sensor.
Foul ? Dry run monitoring
For dry run monitoring in an oil tank of a compressor, for instance, only the lower section of the guide tube is necessary for the measurement. In cases like this, top of the measuring point of the application (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 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 beginning with the sealing face. In this instance, 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. If you 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: