The basics don’t change much “’Sensing elements themselves are pretty stable in that they don’t tend to change,’ says Paul Gobeille, Stellar senior automation engineer. “For example, you’ll find that the theories behind thermocouples (T/Cs), RTDs (resistance temperature detectors), thermistors and infrared (IR) sensors presented in various sources are virtually the same as when they first appeared. So, while temperature sensing technologies don’t change, there are other challenges and many new developments in sensors. “For example, a recent food temperature measurement probe application required exposure to 250°F media and had to be NFS certifiable, be waterproof to 24 inches immersion in water and consist of non-metallic construction at the point of food contact, says Ron Desmarais, engineering manager for Omega Engineering. “’In this case, we selected PET plastic for the body of the sensor that is in direct contact with the food surface and 316L SS in other areas where metallic materials were allowed,’ he explains. ‘Selecting materials to work in the temperature ranges and in contact with various solid, liquid and gaseous environments is a key consideration in the material selection and design of any new product.’ “For those who would like to use RTDs but haven’t because RTD response times have been inherently slow, Endress+Hauser has come up with a thin-film RTD (TM411) that has the response time of a T/C, says Keith Riley, national product manager, pressure & temperature products. “’Traditional RTDs in a 9-mm thermowell have a t90 response time [the time needed for 90 percent of the process step change to be reflected in the output signal] of approximately 20 to 45 seconds depending upon the technology [wire wound/thin film] and geometry [straight/reduced/tapered] utilized. Endress+Hauser’s QuickSens RTDs can reduce the t90 performance of a probe in a 9-mm thermowell to approximately five to 20 seconds depending upon the geometry. This provides end users with the stability and accuracy of a typical RTD measurement and speed of response of a T/C,’ says Riley. “Indirect IR thermometry is fast—typically on the order of milliseconds, according to Ircon’s (now part of Fluke Process Instrumentation) online Noncontact Infrared Temperature Measurement guide. There are certain applications that lend themselves to this technology, according to Ircon. For example:
- Checking the temperature of food exiting a flash cooler
- Measuring the temperature of cereals at the exit of puffers and flakers
- Checking the temperature of soup as it’s cooked in large vats—as well as liquids and vegetables in plastic or glass containers
- Measuring the temperature of products inside ovens and roasters.
- At least store readings internally for USB upload at a later point to a computer, or
- Have Wi-Fi interfaces to upload directly to a plant-wide network or
- Work in tandem with a user’s smartphone or tablet using Bluetooth to process data and upload to a local network or even a cloud-based system.