10 tips sensors To Ensure Accurate Temperature measurement Thermocouple EMF vs. Temperature 80 70 60 E J Millivolts (mV) K 50 40 30 N From choosing the right sensor for your particular process application to the periodic recalibration of that sensor, these tips can help you ensure temperature measurement accuracy and get the most out of your process. BY GARY BARNHARD AND RICHARD C. PALUCH, CONAX BUFFALO TECHNOLOGIES LLC T 20 10 0 R S B Source: Manual in the Use of Thermocouples in Temperature Measurement, 4th Edition, ASTM, 1993, Philadelphia. This schematic depicts EMF curves for various thermocouple types. Selecting the right sensor assembly for your application is the first step in ensuring accurate temperature measurement. C KEY BENEFIT areful selection and installation of temperature sensors can ensure accurate sensor performance, which in turn improves product quality and production efficiency. TIP 1: Select the Correct Sensor Assembly for the Application This may seem self-evident, but it is surprising how often process efficiency is hampered by using the wrong ther- mocouple type. Factors such as time at temperature, degree of accuracy, thermal cycling rate and environment may impact the selection of the best thermocouple type to produce accurate, reliable, long-term performance. For most applications with operating temperatures of 1,400°F (760°C) or less, any of the base metal calibrations (J, E, T and K) will function, but all are not created equal. Type J offers the widest range of environments, including vacuum, oxi- EQUIPMENT COVERED Types E, J, K, T, R, S, B and C thermocouples, leadwire, insulation Understanding measurement accuracy and selecting the proper temperature sensors can improve product quality and production efficiency. 0 100 200 300 400 500 600 700 800 900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700 1,800 1,900 2,000 2,100 2,200 2,300 2,400 Temperature (°C) dizing, reducing and inert atmospheres over the temperature range of 32 to 1,400°F (0 to 760°C). Above 1,000°F (538°C), however, the iron leg is susceptible to rapid oxidation, and below 32°F, the iron experiences rusting and embrittlement. Type T is preferred for lower temperatures, including subzero (-330°F [-200°C]), and is resistant to corrosion in moist atmospheres. In air or oxidizing atmospheres, however, oxidation of the copper thermoelement occurs at INDUSTRIES SERVED Chemicals/petrochemicals, electronics, finishing, food, packaging/printing, pulp/paper/converting, pharmaceuticals, plastics, textiles