A clean sensor leads to reliable measurements

Reliable measurements are essential in industry, whether it is pH measurement, oxygen measurement, determination of brix values, conductivity measurement, optical measurement or spectrometric analysis. There are a number of conditions to ensure correct measurements: choosing the right sensor, installing it in the correct location, continuous accessibility and the sensor must always be clean. Martin Hoogedoorn, business unit manager Process and Dirk Vleminckx, application specialist at Elscolab elaborate on keeping sensors clean.

"Sensors must be clean to generate reliable measurement results. There are many process lines where precipitation reactions create a layer of contamination on the sensor. This leads to erroneous measurements. It is therefore important to clean the sensor regularly and cleanly," Hoogedoorn begins. "Mechanical with a cloth is often not the best solution. There are many suitable solutions and solvents that can clean measurement electrodes much better and faster," Vleminckx adds. "In some processes, frequent cleaning - several times a day - is necessary. Then, for example, it is important to automate."

In situ cleaning systems

Automation can be done in several ways. Hoogedoorn: "With in situ cleaning systems, the sensor remains positioned in the measuring position and is cleaned at that spot. For example, you can ultrasonic clean so that the layer that has formed on the electrode disappears. You can automate this by adding intelligence so you clean the electrode in situ via a fixed time interval or a weekly program."

Retractables

Working with so-called retractables is another option. Hoogedoorn: "The sensor sits in a holder that has both a measuring mode and a maintenance mode. If the sensor needs to be cleaned, the sensor is fully automatically removed from the measurement mode and brought into a rinse chamber where it is treated with a solvent or hot/hot water." In addition to cleaning, automated calibration is also possible. Vleminckx: "For example, if you use an oxygen sensor in the process, then you can use nitrogen to check and validate whether the measurement is still responding to changes."

Advantages

"A major advantage of automated cleaning and calibration is that the process does not have to be shut down since there is a measurement and maintenance mode. The output signals to the process are temporarily frozen, as it were, so that the process controls are not affected," Vleminckx said. Automatic cleaning provides more benefits. Hoogedoorn: "Automatic cleaning is already widely used in the chemical industry. We recently carried out an installation in a phosgene plant. Here this system was chosen to prevent employees in the plant from possible exposure to hazardous substances. In other situations, especially the time savings it provides is an important reason. In some processes it is necessary to clean several times a day. Manual cleaning is then very time-consuming, while many companies are already struggling with staff shortages." Vleminckx adds. "Incidentally, experience shows that if you clean preventively more often, this has a positive effect on the quality of the measurement and on the life of the sensor. In many situations it is better to clean briefly once an hour than very thoroughly once a day."

"We also see a growing interest in the pharmaceutical industry for the combination of cleaning and validation," he continues. "People want to eliminate manual errors, while cleaning and validating are always done according to the same protocol. You are no longer dependent on your employees and you have an accelerated reliable method that ensures that the next process step can be deployed faster."

Custom advice

Automatic cleaning can be very simple, but also very elaborate. "Companies can come to Elscolab for advice on the choice of sensor, its implementation in the process and the cleaning and calibration method. We always take into account the application, the desired result and the available budget," Hoogedoorn concludes.