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 short article describes what needs to be taken into account.
With a reed-chain level sensor, the guide tube contains a defined number 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, 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 example, enables measuring ranges with contact distances between 3 and 24 mm. However, a reed chain can’t be stretched along the entire length of the guide tube. This is due to there are ?dead bands? at เกจวัดแรงดันลมราคา of the tube, i.e. sections that the float does not detect due to design constraints (see graphic).
The graph shows how 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 your two dead bands specified in the data sheet. Within this range, it is usually freely defined. However, it is by no means necessary to utilise the utmost possible measuring range in all applications. The precise adaptation of the number 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 within an oil tank of a compressor, for instance, only the lower area of the guide tube is necessary for the measurement. In this case, top of the measuring point of the application (100 % mark) is set 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 this case, the guide tube could be adapted to the length of the measuring range.
Note
Further information on the RLT series level sensors can be found on the WIKA website. Should you have any questions, your contact will gladly help you.
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: