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 needs to be taken into account.
With a reed-chain level sensor, the guide tube includes a defined amount of reed contacts, based on the 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 based on the liquid level.
Accuracy depends on the length between the contacts
The accuracy of this energy-free level monitoring depends, subsequently, on the distance between the individual contacts: small 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 length 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).
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 an even sensor therefore lies between the two dead bands specified in the info sheet. In this range, it might be freely defined. However, it really is by no means essential to utilise the maximum possible measuring range in all applications. The precise adaptation of the amount of contacts to the measuring task also offers an economic advantage: The reed chain is one of the priciest components in a level sensor.
World ? Dry run monitoring
For dry run monitoring in an oil tank of a compressor, for example, only the lower part of the guide tube is necessary for the measurement. In this case, top of the measuring point of the application form (100 % mark) is defined correspondingly low. It marks the length 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 determined beginning with the sealing face. In this case, the guide tube can be adapted to along the measuring range.
Note
Further information on the RLT series level sensors are available on the WIKA website. If 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?
You can also find out more about float-based level measurement using a reed chain in the next video: