A float-based level sensor with a reed chain is really a widely used and comparatively economical solution for continuous level measurement in vessels. Secret can define its measuring range flexibly within a given range. This article describes what should be taken into account.
With a reed-chain level sensor, the guide tube contains a defined amount of reed contacts, with respect to the measuring range. They are combined to form a measuring chain. The contacts respond 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, in turn, on the distance between your individual contacts: small it is, the more accurate the measurement. Each level sensor in WIKA?s Fully , for example, enables measuring ranges with contact distances between 3 and 24 mm. However, a reed chain can’t be stretched along the entire amount of the guide tube. Simply because 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) 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 usually is freely defined. However, it really is by no means necessary to utilise the maximum possible measuring range in all applications. The precise adaptation of the number of contacts to the measuring task also has an economic advantage: The reed chain is among the priciest components in an even sensor.
Example ? Dry run monitoring
For dry run monitoring within an oil tank of a compressor, for instance, only the lower section of the guide tube is needed for the measurement. In cases like this, top of the measuring point of the application (100 % mark) is set correspondingly low. Outrageousness marks the distance 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 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. In case you have any questions, your contact will gladly help you.
Also read our articles
Level sensors ? 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: