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 inside a given range. This 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, depending on 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.
Accuracy depends on the distance between the contacts
The accuracy of the energy-free level monitoring depends, subsequently, on the distance between the 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 along the entire amount of the guide tube. Simply because you can find ? Weak ? 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 isn’t a must
The measuring selection of an even sensor therefore lies between your two dead bands specified in the info sheet. Within this range, it really is freely defined. However, it really is by no means essential to utilise the maximum possible measuring range in every applications. The exact adaptation of the amount of contacts to the measuring task also offers an economic advantage: The reed chain is among the priciest components in a level sensor.
Overcome ? Dry run monitoring
For dry run monitoring in 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 form (100 % mark) is set 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 beginning with the sealing face. In this instance, the guide tube can be adapted to along the measuring range.
Note
More info on the RLT series level sensors are available on the WIKA website. When you have any questions, your contact will gladly help you.
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Level sensors ? the agony of choice
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You can also find out more about float-based level measurement utilizing a reed chain in the following video: