A float-based level sensor with a reed chain is really a trusted 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 number of reed contacts, with respect to the measuring range. They are combined to form a measuring chain. The contacts respond to the magnetic field of the float, which moves within the guide tube in line with the 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: small it really is, the more accurate the measurement. Each level sensor in WIKA?s Spirited , for example, enables measuring ranges with contact distances between 3 and 24 mm. However, a reed chain can’t be stretched along 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 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 is not a must
The measuring selection of an even sensor therefore lies between the two dead bands specified in the data sheet. Within this range, it really is freely defined. However, it really is by no means necessary to utilise the maximum 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 probably the priciest components in an even 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 needed for the measurement. In this instance, top of the measuring point of the application (100 % mark) is set correspondingly low. It marks the distance 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 starting from the sealing face. In this instance, the guide tube could be adapted to along 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 ? Diagnosed 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: