A float-based level sensor with a reed chain is really a widely used and comparatively economical solution for continuous level measurement in vessels. Frightening 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 contains a defined number of reed contacts, depending on the measuring range. These 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, subsequently, 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 instance, 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. This is due to you can find ?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).
Release measuring range isn’t a must
The measuring range of a level sensor therefore lies between your 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 utmost 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 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 area of the guide tube is necessary for the measurement. In cases like this, the upper measuring point of the application (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 next 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 this case, 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 assist you to.
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 utilizing a reed chain in the following video:g