Reed level sensor: Defining the measuring range flexibly

A float-based level sensor with a reed chain is really 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 needs to be taken into account.
With a reed-chain level sensor, the guide tube includes a defined number of reed contacts, depending on measuring range. They are combined to create 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, in turn, 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 instance, 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. This is due to there are ?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 a level sensor therefore lies between your two dead bands specified in the info sheet. Within this range, it is usually freely defined. However, pressure gauge octa is by no means essential to utilise the utmost possible measuring range in every applications. The precise adaptation of the amount of contacts to the measuring task also has an economic advantage: The reed chain is one of the priciest 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 area of the guide tube is needed for the measurement. In this instance, top of the measuring point of the application form (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 ? diaphragm seal ? 100 % mark X
Consequently, the measuring range for detecting a maximum level is set beginning with the sealing face. In this case, the guide tube can 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. When you 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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