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 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, depending on measuring range. They are combined to form a measuring chain. The contacts react 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 your individual contacts: the smaller it 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 amount of the guide tube. The reason being 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).
Solution 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 selection of an even sensor therefore lies between your two dead bands specified in the data sheet. In this range, it usually is freely defined. However, it is by no means necessary 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 an even sensor.
Example ? Dry 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 this case, the upper measuring point of the application form (100 % mark) is set 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 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. Assuming you have any questions, your contact will gladly assist you to.
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 utilizing a reed chain in the following video: