Measuring instruments ensure maximum process reliability and efficiency. These sensors feature a certified hygienic design and are resistant to high temperatures, pressures and aggressive cleaning processes.

In the food industry, level and pressure measurement technologies are based on sensors to ensure hygiene and reliability, capable of monitoring volumes of ingredients and fluids, such as in cleaning in place, preventing spills and dispersions during mixing and heat treatment, and ensuring that microorganisms do not accumulate in tanks, reducing the costs and dangers associated with contamination.

Continuous level control

Constant monitoring and accurate determination of the fill level, volume or mass in storage tanks, fermentation tanks or other process reactors are essential for efficiency in the food and beverage industry. Hydrostatic, potentiometric and weight measurement systems offer reliable and accurate solutions. The choice of appropriate level measurement methods is influenced by a wide range of parameters, including: tank geometry (type, size, shape, construction material and orientation), the desired degree of measurement accuracy, characteristics of the fluid being processed (liquid, viscous, foaming, conductive or dielectric), environmental and operating conditions (fluid density and temperature, product variation or staticity within the process, tank position, atmospheric or pressurised operating pressure, ease of access and maintenance requirements. As a result, the market offers a wide range of sensing technologies and instrument configurations to meet different application requirements.

Hydrostatic level sensors

Hydrostatic pressure is the pressure that a static fluid exerts uniformly on all surfaces of its container and always acts vertically. As the liquid level rises, so does the pressure. A sensor, located at the bottom of the container, is able to detect these pressure fluctuations and communicate them to the PLC. Since the pressure is exerted omnidirectionally, the sensor can be installed either at the bottom of the tank or on the side, near the lower edge, choosing the configuration that is most suitable for the application context.

To transmit the acquired data to the PLC, pressure transmitters use a piezoelectric signal converter that transforms the mechanical stress detected by the diaphragm into a proportional electrical signal, which is then converted into a standard signal. Modern measurement systems offer the possibility of converting pressure values directly into units of volume or mass, even with dynamic temperature curves, provided that the geometry of the container, the characteristics of the fluid and the operating temperature are determined.

In an open vessel, i.e. at atmospheric pressure, it is sufficient to install a pressure sensor at the bottom of the vessel, as the external pressure conditions remain unchanged. In a pressurised system, i.e. a closed system, the pressure varies and two sensors are required to measure the pressure at the bottom and at the top separately. The difference between the two values (differential pressure) provides the correct measurement of the fill height. When handling fluids subject to thermal fluctuations, a combination of instruments is used, including a piezoelectric transducer and an integrated temperature sensor, to measure both the pressure and temperature of the fluid simultaneously.

This allows for the correction of measurement errors resulting, for example, from changes in fluid density related to changes in process temperature or pressure. Hydrostatic level measurement is particularly suitable for large volumes of liquids in receiving tanks, storage tanks or mixing tanks. The latest generation devices are also suitable for smaller process vessels, both vertical and horizontal, and can be adapted to any height, volume, material or geometry. These systems operate effectively in both indoor and outdoor installations, even in environments characterised by high humidity and low temperatures. In the latter case, problems such as measurement drift or instability caused by water vapour condensation can be mitigated by using a separate, hermetically sealed atmospheric pressure measurement system. This isolation prevents the ingress of gas and moisture, ensuring the accuracy of the measured values.

Potentiometric measurement

Potentiometric measurement sensors consist of an electronic unit and a measuring rod that protrudes into the liquid in the tank. These instruments determine the fill level by monitoring changes in the voltage ratio along the immersed rod. Installation is flexible: it can be done from the top, bottom or side of the vessel, even using probes with a curved profile. Detecting the immersion status of the electrode in the fluid ensures that there are no false readings typically generated by product deposits or foam formation.

Potentiometric measurement is ideal for process, feed and storage tanks, whether open, closed or pressurised. Its insensitivity to foam and adhesions, combined with excellent accuracy and fast response time, makes it a viable solution for a wide range of products and processes in various food sectors, such as dairy and beverage processing. These sensors are ideal for use in milk heaters, filling lines, ice cream production plants, separators, horizontal tanks, process feed tanks, mixers and pressurised vessels.

Pressure sensors

Pressure is constantly monitored using hygienic pressure sensors. These allow positive or negative (vacuum) pressure to be measured in pipes, process vessels and storage tanks. Pressure sensors operate by converting the physical force exerted by a fluid into a proportional electrical signal. The deformation undergone by the transducer’s sensitive element ( ) is converted into a signal (analogue or digital) that can be processed by external supervision and control systems.

The devices can be configured to measure pressure relative to vacuum, where the deformation is related solely to external pressure, detect the difference between process pressure and ambient atmospheric pressure, and determine the differential pressure between two distinct points. In hydrostatic level measurement, the pressure sensor installed at the bottom of the container measures the height of the liquid column, and therefore the level, using the principle of hydrostatic pressure. Smart pressure gauges are able to integrate the geometry of the tank, compensate for the effects of density and temperature, and convert the measured pressure value into units of volume or mass (kg, litres or percentage), even in the presence of fluctuations in temperature and fluid density.

Two pressure values can be acquired simultaneously in pressurised vessels such as fermenters, using sensors equipped with two detection elements and dedicated signal converters. This allows the differential pressure between the bottom and the top to be determined, for example, to monitor the risk of contamination resulting from a drop in pressure. Pressure sensors can be mechanical pressure gauges equipped with a visual indicator for reading the value, or electronic transmitters.

The latter use a piezoelectric converter that processes the measured value and sends it to the PLC as a standard signal. Those for the food industry must comply with the construction and performance criteria defined by bodies such as 3-A, EHEDG and FDA, strictly following sanitary design. Some specific models are designed to operate in extreme conditions, withstanding high process temperatures (250°C), high pressures (up to 1000 bar) and significant pressure peaks.

Radar and ultrasonic technology for level measurement

Mechanical pressure detection devices can be susceptible to damage during cleaning in place (CIP) cycles or internal equipment checks. In addition, their measurement reliability can be compromised by the presence of foam or difficulty in accurately determining the “zero level”, especially if the sensor is not installed coplanar with the base of the tank. Radar technology, on the other hand, offers continuous, high-precision level reading with high resolution. It remains effective even in the presence of h r interference, foam or vapour, and does not present any risks associated with wear or mechanical breakage.

The operating principle is based on the emission of electromagnetic pulses that propagate to the surface of a liquid or solid. These pulses are reflected and captured again by the sensor. By calculating the time of flight (ToF) or frequency modulation (Frequency Modulated Continuous Wave, FMCW), the distance from the interface surface is determined and then converted into the actual level inside the tank. Ultrasonic technology is also used in the food industry to determine the level of liquids inside tanks.

The probes emit sound waves and measure the echo return time to calculate the distance from the surface of the fluid, such as juices, milk, oils, or bulk solids, such as cereals, flours, sugar, and powders. This technology is not suitable for pressurised environments or in the presence of high foam concentrations.