เกจแรงดันน้ำ -based level sensor with a reed chain is 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 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. They are combined to create a measuring chain. The contacts respond 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 the individual contacts: small it really 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 along the entire length of the guide tube. For the reason that there are ?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 the way 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 selection of an even sensor therefore lies between your two dead bands specified in the data sheet. In this range, it really is freely defined. However, it is by no means essential 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 probably 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 portion of the guide tube is necessary for the measurement. In cases like this, 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 set starting from the sealing face. In cases like this, the guide tube can be adapted to the length of the measuring range.
Note
More info on the RLT series level sensors can be found 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 preference
What do dead bands mean with a float switch?
There are also out more about float-based level measurement utilizing a reed chain in the next video: