A float-based level sensor with a reed chain is really a trusted 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, with regards to the measuring range. They are combined to create 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 distance between the contacts
The accuracy of the 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 across the entire length of the guide tube. The reason being you can find ?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 the way 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 selection of an even sensor therefore lies between the two dead bands specified in the info sheet. In this range, it is usually freely defined. However, it is by no means necessary to utilise the utmost 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 among the most expensive 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 portion of the guide tube is necessary for the measurement. In cases like this, top of the measuring point of the application (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 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 along the measuring range.
Note
More info on the RLT series level sensors are available on the WIKA website. When Validate have any questions, your contact will gladly assist you to.
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 using a reed chain in the following video: