The document discusses using a draw-wire displacement sensor to continuously measure the filling quantity in biogas tanks. As the gas in the tank increases pressure, it inflates the flexible film of the gas tank. A weight attached to the film keeps the sensor wire tensioned so the sensor can measure the changing distance as the film expands and contracts based on gas quantity. This continuous measurement allows for more efficient control of biogas generation compared to discrete level switch measurements, improving the efficiency of biogas production and combustion.

1. A159_e
Draw-wire displacement sensor
wireSENSOR
Filling quantity measurement in biogas tanks
Biogas is a modern renewable energy
source and potentially a lucrative source
of income for many farmers. Its special
Sensor
feature is the generation of electricity,
heat and fertiliser from biomass.
Combustible gases are produced by Foto Biogasanlage gesamt
anaerobic fermentation and putref-
Generator
action processes.
Depending on the source material,
biogas basically contains methane,
carbon dioxide and water vapour. A
fermenter consists of an airtight round
Gas tank Control unit
silo, which is connected to a gas tank
made of a film.
The objective is to create a constant Fermenter
fermentation process so that the
combustion can take place constantly with maximum The distance between film and displacement sensor
efficiency. increases as the filling quantity in the gas tank decreases.
Depending on the gas quantity, the gas tank film inflates
due to increasing pressure. The fill quantity to be The control unit reduces the speed of the generator due to
fermented can be determined from the bulge of the film. To the increase of the displacement signal in order to restore
date, inductive limit switches which measure the bottom, the target fill quantity in the gas tank.
middle and top position of the film have been used to Therefore, the efficiency of the biogas generation and
measure this. combustion is increased many times as the fill quantity is
This discrete measurement of the fill quantity did not take measured at each point in time of the fermentation
account of the inertia of the fermentation process and process and new fermentation material can be added if
made the control of the biogas generation inefficient. necessary.
The fill quantity in the fermenter can be measured
continuously by using draw-wire sensors. A weight is Reasons for selecting the system:
attached to the film for a constant pressing force, which - price/performance ratio
keeps the sensor wire tensioned. The sensor is located in - robust design
the generator building and is connected to the weight on
the film using wire extensions. The measured distance Suitable sensor series:
also changes as the expansion of the film changes. - WDS-xxxx-P96
- WDS-xxxx-MK77
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