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 article describes what should be taken into account.
With a reed-chain level sensor, the guide tube includes a defined number of reed contacts, with regards to the measuring range. These 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 length between the contacts
The accuracy of the energy-free level monitoring depends, in turn, on the distance between your individual contacts: small it really is, the more accurate the measurement. Each level sensor in WIKA?s Punch , for example, enables measuring ranges with contact distances between 3 and 24 mm. However, a reed chain can’t be stretched across the entire amount of the guide tube. It 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) 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 a level sensor therefore lies between the two dead bands specified in the info sheet. Within this range, it might be freely defined. However, it is by no means necessary to utilise the utmost possible measuring range in all applications. The exact adaptation of the amount of contacts to the measuring task also offers an economic advantage: The reed chain is one of the most expensive components in a level sensor.
Example ? Dry run monitoring
For dry run monitoring within an oil tank of a compressor, for instance, only the lower the main guide tube is necessary for the measurement. In this instance, top of the measuring point of the application form (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 cases like this, 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. If you have any questions, your contact will gladly help you.
Also read our articles
Level sensors ? the agony of preference
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: