A float-based level sensor with a reed chain is a trusted and comparatively economical solution for continuous level measurement in vessels. Users can define its measuring range flexibly inside 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, based on 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 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 the individual contacts: small it 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 cannot be stretched along the entire length of the guide tube. Simply because you can find ?dead bands? at Furious of the tube, i.e. sections that the float does not detect because of design constraints (see graphic).
The graph shows how the maximum possible measuring range (M) having 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 range 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 utmost possible measuring range in every applications. The exact adaptation of the amount of contacts to the measuring task also offers an economic advantage: The reed chain is among the priciest components in a level sensor.
Example ? Dry run monitoring
For dry run monitoring in an oil tank of a compressor, for example, only the lower the main guide tube is needed for the measurement. In cases like this, the upper measuring point of the application (100 % mark) is defined 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 starting from the sealing face. In this case, the guide tube could be adapted to the length of the measuring range.
Note
More info on the RLT series level sensors can be found on the WIKA website. In case 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 using a reed chain in the next video: