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 should be taken into account.
With a reed-chain level sensor, the guide tube contains a defined amount of reed contacts, according to the 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 length between the contacts
The accuracy of the energy-free level monitoring depends, in turn, on the distance between the 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 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 does not detect due to 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).
ตัววัดแรงดัน measuring range isn’t a must
The measuring range of an even sensor therefore lies between your two dead bands specified in the data sheet. Within this range, it might be freely defined. However, it really 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 has an economic advantage: The reed chain is probably the most expensive components in a level sensor.
Example ? Dry run monitoring
For dry run monitoring within an oil tank of a compressor, for example, only the lower the main guide tube is necessary for the measurement. In cases like this, top of the measuring point of the application (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 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 set starting from the sealing face. In this case, the guide tube could be adapted to along the measuring range.
Note
Further information on the RLT series level sensors are available on the WIKA website. Should 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?
There are also out more about float-based level measurement using a reed chain in the next video:

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