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 article describes what must be taken into account.
With a reed-chain level sensor, the guide tube includes a defined number of reed contacts, with respect 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 good 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 cannot be stretched across the entire amount of the guide tube. For Refund that 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 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 range of a level sensor therefore lies between the two dead bands specified in the data sheet. In this range, it can 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 number 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 in an oil tank of a compressor, for instance, 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 process 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 determined starting from the sealing face. In this case, 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. When you have any questions, your contact will gladly help you.
Also read Create ? the agony of choice
What do dead bands mean with a float switch?
There are also out more about float-based level measurement using a reed chain in the next video:g