Temperature Basics Bill Bergquist, Sr. Applications Engineer Jeff Wigen, National Sales Manager Bill Jeff © Burns Engineering Temperature Basics Agenda 2 Temperature Defined Temperature Scales Types of Temperature Sensors Thermocouple Types Temperature ranges Lead wire colors Standards RTD Temperature coefficient Construction Calibration Interchangeability Standards Identification of Sensor Types Sensor Selection - The Four Ps Calibration Preventive Maintenance © Burns Engineering Temperature Basics Temperature 3 What is temperature? Measure of the average kinetic energy of particles in a substance. Temperature is the result of the motion of particles. Temperature increases as the energy of this motion increases. Physical quantity that is a measure of hotness and coldness on a numerical scale. © Burns Engineering Temperature Basics Temperature 4 Temperature of some things: ¾ Ice 32°F ¾ Dry ice −78.5°C (−109.3°F) at atmospheric pressure ¾ Liquid nitrogen -196°C ¾ “Fahrenheit 451” (Ray Bradbury) approximate auto-ignition point of some paper ¾ Sun 5700K (5430°C) ¾ Earth’s core 5700K (5430°C) (cooling at 100°C per billion years). The core may contain enough gold, platinum, and other siderophile elements that if extracted and poured onto the Earth's surface, would cover the entire Earth with a coating 0.45 m (1.5 feet) deep. ¾ Lightning bolt 50,000K ¾ Earth’s average surface temperature – good luck trying to figure out that one! ¾ In photography K (Kelvin) is used to denote color temperature. Match flame is about 1700K, sunshine is about 5400K. © Burns Engineering Temperature Basics Temperature Scales 5 Celsius The Celsius scale is widely used in industry Swedish astronomer Anders Celsius (1701–1744) with the Fahrenheit scale a close second. By international agreement the unit "degree Celsius" and the Celsius scale are currently defined by two different temperatures: absolute zero, and the Kelvin is almost exclusively used for scientific triple point of VSMOW (Vienna Standard Mean Ocean Water). and laboratory measurements. Triple point of water is defined as 273.16K or 0.01°C, the point at which water exists as a vapor, solid, and liquid. A degree Celsius (or a Kelvin) is what you get when divide the thermodynamic range between absolute zero and the triple point of water into 273.16 equal parts. In 1948, it was renamed Celsius because centigrade had other meanings in Spanish and French. © Burns Engineering Temperature Basics Temperature Scales 6 Kelvin A Kelvin or K does not have a degree symbol. One of the seven base units in the SI system of units named after the Belfast-born, Glasgow University engineer and physicist William Thomson, It is used by itself such as 273K. On 1st Baron Kelvin (1824–1907) calibration reports you will see the calibration Based on absolute zero which is 0K, or −273.15°C or −459.67°F. uncertainty expressed in millikelvin or mK so Theoretical point at which all thermal motion stops. 1mK is 0.001K. Fahrenheit Temperature scale based on one proposed in 1724 by the physicist Daniel Gabriel Fahrenheit (1686–1736) freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees — on Fahrenheit's original scale the freezing point of brine was zero degrees. © Burns Engineering Temperature Basics Various Temperature Sensors 7 • Liquid displacement thermometers There are other types of sensors that have • Dial thermometers little practical use or are still in development • Thermistors • Optical (DTS, IR) such as the Johnson Noise Thermometer, • Thermocouples and a device that uses a laser as a measure. •RTD’s RTDs and Thermocouples Infrared Dial Thermistors Bimetal coil © Burns Engineering Temperature Basics Thermometers 8 Liquid Displacement Dial Mercury-in-glass is probably the most well Both have . known liquid displacement type of Limited temperature ranges thermometer. Other types of fluid are used Limited accuracy with some used to deflect a needle that Industrial integrity indicates temperature. Introduce human error © Burns Engineering Temperature Basics Thermistors 9 • Very precise • Ceramic, silicon, or polymer resistor As temperature increases the resistance • High resistance values increases and can be correlated to a • Very limited temperature range temperature. • Often have drift error • Self-heating errors •Low price © Burns Engineering Temperature Basics Thermocouples 10 Made by connecting two different metals to form a closed circuit. As temperature increases, the measured High durability voltage increases and does so in a Low initial cost Voltage change with temperature predictable manner. The thermocouple standards define the voltage vs. temperature + relationship for several types of thermocouple junctions. - © Burns Engineering Temperature Basics Thermocouples 11 2500 2156 2000 1500 1600 1400 1200 Temp 1000 700 F 500 32 32 32 -328 -328 -450 -328 Type T Type E Industrial RTD Thermocouples © Burns Engineering Temperature Basics Thermocouples 12 Types Most common • Type T: Copper-Constantan Red/Blue • Type J: Iron-Constantan Red/White • Type E: Chromel-Constantan Red/Purple • Type K: Chromel-Alumel Red/Yellow High temperature types • R, S, B Platinum/Platinum-Rhodium 2640°F • W3, W5 Tungsten/Tungsten-Rhenium 4200°F Each type has a different temperature range and Voltage vs. Temperature relationship ASTM Standard E230 , ANSI MC 96.1, and IEC 584-3 © Burns Engineering Temperature Basics Thermocouples 13 Junctions can be grounded, ungrounded or exposed. © Burns Engineering Temperature Basics Thermocouples Advantages Disadvantages Very wide temperature Decreased accuracy vs. Thermocouples are typically used in an Range [1.2K to 2300°C] RTDs application where high temperature or high Fast Response Time More susceptible to vibration is present. Their durability is Available in small sheath RFI/EMI sizes Recalibration is difficult probably their best asset. Low initial cost Requires expensive TC wire from sensor to recording Durable device Difficult to verify Not as stable as RTDs © Burns Engineering Temperature Basics Resistance Temperature Detector 15 RTDs 3 common element styles The platinum resistance thermometer (PRT) Coil in the hole is the most widely used sensor type in Wire wound applications where highly accurate, Thin film repeatable and stable measurements are Resistor made from platinum, nickel, copper, or other metals required. Other metals are used but none have the wide temperature capability of platinum. © Burns Engineering Temperature Basics RTD 16 Basic Operation Resistance changes with temperature. As temperature increases, resistance increases in response. Small current is sent through the resistor element and electrical resistance is measured Performance defined by IEC 60751 and ASTM E1137 © Burns Engineering Temperature Basics RTD 17 Basic Operation When specifying an RTD it is necessary to Temperature coefficient select the correct temperature coefficient to • Also called the Temperature Coefficient of Resistance or alpha match the readout instrument or controller. • Units are ohms/ohm/°C Failure to do so will result in an inaccurate • The average change in resistance per unit change in measurement. temperature between 0 and 100°C • α = R100 -R0 / 100°C*R0 »R0 = resistance at 0°C »R100 = resistance at 100°C For the current industry standard 100 ohm RTD the alpha is .00385 which means at 100°C the nominal sensor resistance is 138.5 ohms © Burns Engineering Temperature Basics RTD 18 Most common coefficients • 0.00385 – ASTM E1137 or IEC 60751 • 0.003902 – American • 0.003916 – JIS • 0.003925 - SPRT, Secondary SPRT Must match your instrument to the proper temperature coefficient of your sensor © Burns Engineering Temperature Basics RTD 19 Coefficient example A temperature is being measured with a sensor having a temperature coefficient of .003916 (JIS) but due to a sensor failure it was replaced with a sensor having a temperature coefficient of .00385. If the transmitter/controller is not recalibrated, at 100°C it will read 1.7°C low. © Burns Engineering Temperature Basics Interchangeability 20 RTDs are manufactured to have 100 ohms at 0°C. The two main standards in use today are the IEC 60751 and the ASTM E1137. Both have Interchangeability refers to the “closeness of agreement” between an actual PRT R vs. T relationship and a predefined R vs. T the same nominal R vs. T values but differ in relationship. defining some performance characteristics and the tolerances associated with the Defined by ASTM E1137 and IEC 60751 grades or classes of sensors. The Nominal R vs. T of ASTM and IEC standards are equivalent but interchangeability tolerances are the target tolerances are different. that manufacturers shoot for when building the sensing elements. © Burns Engineering Temperature Basics Interchangeability 21 4 IEC Class B Note that the ASTM standard has slightly ASTM Grade B 3 tighter tolerances for the two grades of 2 sensors. All RTDs are built with the tightest IEC Class A ASTM Grade A 1 tolerance at 0°C and as the temperature diverges from 0°C the tolerance increases. 0 -300 -200 -100 0 100 200 300 400 500 600 700 800 The vertical line on the graph represents 0°C Tolerance (±°C) Tolerance -1 ASTM Grade A IEC Class A and the tolerance on the y axis is expressed -2 in ± °C from nominal. ASTM Grade B -3 IEC Class B -4 Temperature (°C) © Burns Engineering Temperature Basics Interchangeability 22 Standard Tolerance Defining Equation¹ These equations can be used to calculate