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 inside a given range. This short article describes what must be taken into account.
With a reed-chain level sensor, the guide tube contains a defined amount of reed contacts, depending on the measuring range. Maul 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 your individual contacts: the smaller 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 amount of the guide tube. This is because you can find ?dead bands? at both ends 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 your two dead bands specified in the data sheet. Within this range, it is usually freely defined. However, it really is by no means essential to utilise the utmost possible measuring range in every applications. The precise adaptation of the amount 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 in an oil tank of a compressor, for instance, only the lower part of the guide tube is needed for the measurement. In this instance, the upper measuring point of the application form (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 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 beginning with the sealing face. In cases like this, the guide tube can be adapted to along the measuring range.
Note
More info on the RLT series level sensors can be found on the WIKA website. For those who 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?
You can also find out more about float-based level measurement utilizing a reed chain in the next video: