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In applications involving cleaning processes, the measurement of conductivity plays a major role in efficient process control. Especially in the food and pharmaceutical sector, reliable phase separation during CIP processes is essential to avoid the risk of contamination and to conserve resources. For the successful implementation of phase separation, the conductivity values of the individual media must be known. However, these are governed by the temperature of the medium. Media such as water or cleaning media are relatively easy to distinguish due to their significantly different conductivity values. Milk products and beverages, however, have much more similar values, which is why conductivity measurement must be very precise. This requires quick and precise temperature compensation of the conductivity value measurements.
In the food industry, there are two main applications in which the phase separation of media plays a significant role:
1. Return of the CIP process for phase separation between cleaning media and water
To prevent contamination, systems in the food industry are cleaned at regular intervals with water, lye, acid, and disinfectants. To minimize the use of resources as much as possible, the cleaning media are collected in batch tanks for reuse during batch cleaning. The efficient control of this process requires a reliable phase separation of the different media. The conductivity values of the different media can therefore be used to determine which medium is in the pipe. The data collected by the conductivity measurement allows the valves to be controlled in such a way that each medium is returned to the correct batch tank. However, the conductivity can be used not only to determine the type of medium but also to specify the optimal time for phase separation, which depends on the mixing phase of the media, among other factors. Depending on the mixing phase, it is necessary to distinguish the point at which the medium can be returned to the batch tank. Therefore, conductivity sensors play a major role in this process and help prevent contamination while keeping the loss of media to a minimum.
In the food industry, there are two main applications in which the phase separation of media plays a significant role:
1. Return of the CIP process for phase separation between cleaning media and water
To prevent contamination, systems in the food industry are cleaned at regular intervals with water, lye, acid, and disinfectants. To minimize the use of resources as much as possible, the cleaning media are collected in batch tanks for reuse during batch cleaning. The efficient control of this process requires a reliable phase separation of the different media. The conductivity values of the different media can therefore be used to determine which medium is in the pipe. The data collected by the conductivity measurement allows the valves to be controlled in such a way that each medium is returned to the correct batch tank. However, the conductivity can be used not only to determine the type of medium but also to specify the optimal time for phase separation, which depends on the mixing phase of the media, among other factors. Depending on the mixing phase, it is necessary to distinguish the point at which the medium can be returned to the batch tank. Therefore, conductivity sensors play a major role in this process and help prevent contamination while keeping the loss of media to a minimum.
2. Emptying or rinsing a storage tank
The loss of valuable products can be very costly. To minimize loss, the product is usually pushed out of the pipes with water and then returned to tanks at the end of a production process. However, this requires that the water is not unintentionally mixed with the product and returned. To prevent this, conductivity sensors are used to determine when water enters the filling system. Even with minute quantities, the system must be immediately switched to prevent contamination of the product.
The loss of valuable products can be very costly. To minimize loss, the product is usually pushed out of the pipes with water and then returned to tanks at the end of a production process. However, this requires that the water is not unintentionally mixed with the product and returned. To prevent this, conductivity sensors are used to determine when water enters the filling system. Even with minute quantities, the system must be immediately switched to prevent contamination of the product.
Mixing phases during phase separation
Determining the exact time of phase separation is not always easy, as there is not always a precise point in time. During phase separation of two media, there is always a so-called mixing phase in which the two media are mixed. The length of this mixing phase depends on the viscosity of the media.
The higher the viscosity, the shorter the mixing phase:
The higher the viscosity, the shorter the mixing phase:
The lower the viscosity, the longer the mixing phase:
Positioning the sensor correctly during phase separation
The mixing phase spreads more quickly in the core flow of the pipe. To achieve a short response time, it is therefore important to position the sensor at the center of the pipe to detect the point of phase separation as early as possible.
Finding the correct trigger point
Selecting the correct trigger point always involves a compromise between food safety and resource conservation. However, a reliable conductivity sensor can ensure both simultaneously.
If, for example, a cleaning medium follows the rinsing water in the CIP cleaning process, a high switching threshold should be selected, as otherwise there is a risk that rinsing water is returned to the batch tank for the cleaning medium when switching occurs too early.
When a product is pushed out, a low threshold should be selected to prevent contamination of the product. If the switching is too slow or too late, there is the risk of milk mixing with water, for example.
- Slow reaction/switching threshold when a product is introduced (T2)
If, for example, a cleaning medium follows the rinsing water in the CIP cleaning process, a high switching threshold should be selected, as otherwise there is a risk that rinsing water is returned to the batch tank for the cleaning medium when switching occurs too early.
- Quick reaction/switching threshold when a product is pushed out (T4)
When a product is pushed out, a low threshold should be selected to prevent contamination of the product. If the switching is too slow or too late, there is the risk of milk mixing with water, for example.
T1: Cleaning medium pushes the rinsing water out, start of the mixing phase
T2: Trigger point reached, practically only cleaning medium
T3: Rinsing water pushes the cleaning medium out, start of the mixing phase
T4: Trigger point reached, cleaning medium is mixed with rinsing water
T5: Practically only rinsing water
T2: Trigger point reached, practically only cleaning medium
T3: Rinsing water pushes the cleaning medium out, start of the mixing phase
T4: Trigger point reached, cleaning medium is mixed with rinsing water
T5: Practically only rinsing water
Temperature compensation
The laws of physics dictate that the conductivity of a medium depends on its temperature. An increase in temperature also increases the conductivity of a medium. To obtain a precise measurement result during phase separation, the temperature values of the medium must be taken into account. However, the temperature dependence differs according to the medium. For this reason, the CombiLyz AFI conductivity sensor measures not only the conductivity but also the temperature of the medium and takes the temperature compensation into account during the measurements. Therefore, a minimum reaction time of the temperature sensor in the conductivity measurement device is an important criterion for the delay-free detection of a phase change.
