Speed and accuracy help to meet stringent quality demands

Both, very accurate temperature control and very fast response to temperature changes are vital for the efficient and safe production of bacterial cultures, which are used for sour milk products such as yoghurt and other types of food. During the UHT (Ultra High Temperature) treatment, the temperature must be kept above 139˚C (282°F) otherwise in the worst-case scenario, the production batch might have to be destroyed.

Tommy Mikkelsen conducted extensive testing of the iTHERM TM411 temperature sensor with convincing results. Its unmatched response time allows continuous process monitoring and enables a constant temperature to be maintained within a very small range. The tests also showed that the predictable negative impact of the thermowell on the overall accuracy was hardly detectable. Thus the recalibration required for this critical device can be performed without interrupting the process.

In the UHT process, a medium is being exposed to temperatures above 139°C (282°F) for a defined time span. Safe sterilization can only be guaranteed if the temperature does not fall below the minimum temperature at any time. Thus, if the temperature drops and comes close to the minimum required temperature, a quick response from the control system is necessary to counteract the temperature decrease. The prerequisite for this reaction is a temperature sensor with a very fast response time.

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Tommy Mikkelsen has conducted response time tests with different temperature sensors which revealed that iTHERM QuickSens technology could reduce response times by more than 50% compared to older sensors! “The new iTHERM TM411 thermometer from Endress+Hauser with QuickSens technology is the perfect choice for this application”, says Tommy Mikkelsen. “ Its unmatched response time allows continuous monitoring of the process and keeping the temperature constant within a very small range.”

A thermowell is the part of the thermometer which hosts the actual sensor (or insert) and protects it from harsh process conditions. This additional barrier between the sensor and the process medium usually negatively affects the performance of the meter. To quantify this expected negative impact on measurement performance, Tommy Mikkelsen has conducted test calibrations both with and without thermowell: measured deviations are below 0.1˚C – regardless of whether there was a thermowell or not!

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Using thermowells offers a significant advantage: during recalibration the process can be kept closed as the thermowell remains in the plant while the sensor itself is removed for calibration. Removing the sensor for recalibration is child’s play: the so-called QuickNeck allows the tool-free removal of the complete upper part of the sensor from the thermowell with just one twist. No need to open the housing or to disconnect any wires – it is simple, safe and fast.

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