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 inside a given range. This short article describes what should be taken into account.
With a reed-chain level sensor, the guide tube contains a defined amount of reed contacts, with respect to the measuring range. These 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, subsequently, on the distance between your 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. Simply because 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) 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 the two dead bands specified in the info sheet. Within this range, it could be freely defined. However, it is by no means essential to utilise the maximum possible measuring range in all applications. The exact adaptation of the number of contacts to the measuring task also offers an economic advantage: The reed chain is one of the priciest components in a level sensor.
Example ? Content run monitoring
For dry run monitoring within an oil tank of a compressor, for example, only the lower section of the guide tube is needed for the measurement. In cases like this, top of the measuring point of the application form (100 % mark) is set correspondingly low. In The Zone marks the length to the sealing face of the process 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 case, 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. In case you have any questions, your contact will gladly help you.
Also read our articles
Level sensors ? the agony of choice
What do dead bands mean with a float switch?
You can also find out more about float-based level measurement using a reed chain in the following video:

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