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Filling level control

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The installation of a suitably precise and hardy closed-loop automation system offers the F&B industry efficiencies in manufacture. Burkert Fluid Control Systems managing director Chris Hoey writes for FOOD magazine

CLOSED-LOOP control is a process that occurs commonly in the manufacture of food and beverages.

The installation of a suitably precise and hardy closed-loop automation system offers the F&B industry efficiencies in manufacture, with closed-loop systems capable of 24/7 operation when associated with appropriate automation.

In principle, closed-loop control appears a very simple process. However, technical implementation and design are complex, and require expert advice from the professionals.

In order to achieve faultless operation of a closed-loop control, the individual components of the control loop componentry must be inter-matched, and the system customised and matched to the comprehensive system at hand.


Frequently the food and beverage industry addresses the process issue of maintaining the level of a fluid across a series of supply tanks, fed from a feed tank that is kept at a constant level.

To achieve this consistently even level across the supply tank series, two level switches are fitted to each supply tank – one each for minimum and maximum filling level. Drop below the minimum filling level is signaled to the master control system via electrical/pneumatic automation system. The diaphragm valve at the supply tank inlet opens, and is shut off once the upper level switch is triggered.

Feed tank filling level is maintained at a consistent level via localised control loop, which continuously and minutely detects the feed tank level. The closed-loop filling level control function is performed by a precise diaphragm control valve, with attached positioner. The positioner incorporates a process controller to whose actual value input the signal output of the level transmitter is connected. The set-point value of the control loop is preset via a signal from the comprehensive electrical/pneumatic automation system.

Mixing in a ratio

One of the most common processes in the food and beverage industry is the mixing of fluids in predetermined ratios, with suitable combined fluid agitation incorporated in the process to ensure a uniform outcome.

The mixing of fluids generally involves fluids being added sequentially to a mixing vat, via solenoid valve, until the established quantities are input. These volumes are determined by the level sensor, based on pre-set filling height and tank dimensions.

The solenoid valve controller closes the diaphragm once the required volume is input, then opening a second solenoid valve for the input of the second fluid – and so on, until all fluids are added. Following addition of the final liquid component, the combine mixture is mixed thoroughly by an agitator with set velocity and time, to ensure homogenous output.

The output fluid is further processed, and finally filled into containers. During the container filling process, the product is added to the vessel until a load cell determines that the required filling capacity has been reached.

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