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 contains a defined number of reed contacts, with regards to the measuring range. These are combined to form 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, subsequently, on the distance between your 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 amount of the guide tube. It is because 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) 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 info sheet. Within this range, it usually is freely defined. However, it is by no means necessary to utilise the maximum possible measuring range in every applications. The exact 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 an even sensor.
Example ? 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 this instance, the upper measuring point of the application form (100 % mark) is defined correspondingly low. It marks the distance 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 ? ไดอะแฟรม , the measuring range for detecting a maximum level is set beginning with the sealing face. In ไดอะแฟรม , the guide tube can be adapted to along the measuring range.
Note
Further information on the RLT series level sensors can be found on the WIKA website. When you have any questions, your contact will gladly help you.
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There are also out more about float-based level measurement utilizing a reed chain in the following video: