Electricity and Control January 2020

MEASUREMENT + INSTRUMENTATION

Self-calibrating RTD temperature sensor in UHT processes Ultra-high temperature processing (UHT) is a food processing technology used to sterilise liquid food products. It is commonly used in milk production. In this article Endress + Hauser sets out the benefits of a smart self-calibrating thermometer developed for use in UHT processes.

The challenge In UHT processes the product is heated to above 135°C to kill as many microorganisms as possible, with the aim of increasing the shelf-life of the product. This requires an optimal combination of temperature and treatment duration for each product. Accurate and reliable temperature control is crucial to avoid negative effects on the taste and product quality, and this means periodic calibration of the installed temperature sensors is necessary. The downtime, process interference and manual documentation effort that this imposes can present a significant challenge to manufacturers, small and big. The solution In order to overcome this challenge, Endress + Hauser developed iTHERM TrustSens, a self-calibrating compact thermometer that calibrates automatically whenever the process temperature drops below 118°C. The device simultaneously verifies the measured process value of the primary temperature sensor (Pt100) against an integrated, traceable and long-term stable fixed-point reference. In this way it ensures that a potentially damaged or defective temperature sensor is reliably detected before each batch

- Higher recalibration frequency maximises process safety. - Fully automated and traceable inline self-calibration eliminates the production downtime needed for manual calibration. - Fully automated, audit-proof calibration certificates make documentation easy. - The iTHERM ensures highest measuring accuracy with transmitter-sensor matching, across a temperature range from -40°C to +160°C. - More than 50 sterile and hygienic process connections are available as standard. - The sensors hold international certifications and approvals including EHEDG, ASME BPE, FDA, 3-A, 935/2004, 2023/2006, 10/2011, CE, CRN, CSA General Purpose. Typically, the UHT process cooling rate after operation is about 10 Kelvin per minute. Active cooling is generally avoided as this can, potentially, induce a strong negative pressure that could damage the system. Cold water is therefore injected only once the temperature drops below 100°C.

run. Self-calibration is performed consistently during every cooling phase after the system is shut down. In UHT applications the iTHERM tempe- rature sensor delivers a number of benefits.

Schematic process temperature curve with indicated sensor self-calibration point.

Key considerations In regulated industries such as the life sciences and food & beverage industries, measuring devices often require multiple calibrations per year. Removing and re-installing probes is generally a time-consuming and costly exercise, especially in large plants. TrustSens is the first intelligent sensor capable of self- calibration, so it obviates the process disruption typically

In ultra-high temperature processing in the food and beverage industry, accurate and reliable temperature control is crucial to avoid negative effects on the taste and quality of the product.

18 Electricity + Control

JANUARY 2020