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 number of reed contacts, depending on 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 the 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 instance, enables measuring ranges with contact distances between 3 and 24 mm. However, a reed chain cannot be stretched along the entire length of the guide tube. For the reason that you can find ?dead bands? at both ends of the tube, i.e. sections that the float does not detect because of design constraints (see graphic).
The graph 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 range of an even sensor therefore lies between the two dead bands specified in the info sheet. In this range, it can be freely defined. However, it is by no means essential to utilise the maximum possible measuring range in every applications. The exact adaptation of the number of contacts to the measuring task also offers an economic advantage: The reed chain is probably the most expensive components in an even sensor.
Example ? Dry run monitoring
For dry run monitoring in an oil tank of a compressor, for example, only the lower part of the guide tube is necessary for the measurement. In this instance, the upper measuring point of the application (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 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 cases like this, the guide tube could be adapted to along the measuring range.
Note
More info on the RLT series level sensors are available on the WIKA website. In case you have any questions, your contact will gladly assist you to.
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There are also out Faux Pas float-based level measurement using a reed chain in the next video: