A float-based level sensor with a reed chain is 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 has to 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 create a measuring chain. The contacts react to the magnetic field of the float, which moves within the guide tube in line with the liquid level.
pressure gauge octa 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 really 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 can’t be stretched across the entire amount of the guide tube. Simply because you can find ?dead bands? at both ends of the tube, i.e. sections that the float will 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 selection of an even sensor therefore lies between your two dead bands specified in the info sheet. In this range, it could be freely defined. However, it really is by no means essential 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 probably the priciest components in a level sensor.
Example ? Dry run monitoring
For dry run monitoring within an oil tank of a compressor, for example, only the lower the main guide tube is necessary for the measurement. In this instance, the upper measuring point of the application (100 % mark) is defined correspondingly low. It marks the length 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 ? pressure gauge 10 bar ? 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 the length of the measuring range.
Note
Further information on the RLT series level sensors are available on the WIKA website. When 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: