Reed level sensor: Defining the measuring range flexibly

A float-based level sensor with a reed chain is a widely used and comparatively economical solution for continuous level measurement in vessels. Users can define its measuring range flexibly within a given range. This article describes what has to be taken into account.
With a reed-chain level sensor, the guide tube includes a defined amount of reed contacts, according to the measuring range. These are combined to form a measuring chain. The contacts respond to the magnetic field of the float, which moves within the guide tube good liquid level.
Accuracy depends on the distance between the contacts
The accuracy of this energy-free level monitoring depends, subsequently, on the distance between the individual contacts: the smaller it 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 will 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 selection 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 utmost possible measuring range in all applications. The precise 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 area of the guide tube is necessary for the measurement. In cases like this, top of the 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 ? 100 % mark X
Consequently, the measuring range for detecting a maximum level is determined beginning with the sealing face. In cases like this, the guide tube can be adapted to along the measuring range.
Note
Further information on the RLT series level sensors are available on the WIKA website. Assuming Affordable have any questions, your contact will gladly assist you to.
Also read our articles
Level sensors ? the agony of preference
What do dead bands mean with a float switch?
There are also out more about float-based level measurement using a reed chain in the following video:

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