231 eal-time & Embedded 1 Systems 2015 Uwe. Zimmer - The Australian National University 233 eal-time Systems Components: Physical coupling Processor Processor Communication Communication munication eal-time Software: Algorithms, Languages, Operating systems, Communication Systems Communication Communication Communication Communication Communication Processor Processor Processor Processor Processor I/O I/O I/O I/O I/O Discrete Analogue -> Digital Analogue -> Digital Digital -> Analogue Analogue -> Digital Digital -> Analogue Sensor Sensor Actuator Sensor Actuator Analogue Physical phenomena Environment / World 2017 Uwe. Zimmer, The Australian National University page 233 of 932 (chapter 1: up to page 262) 232 eferences [ Edler2003 ] Edler et al. Noise temperature measurements for the determination of the thermodynamic temperature of the melting point of palladium. Metrologia (2003) vol. 41 (1) pp. 47-55 [Peacock97] G.. Peacock Standards for temperature sensors. http://www.temperatures.com/resources/standards/ (1997) (additional data-sheets) 2017 Uwe. Zimmer, The Australian National University page 232 of 932 (chapter 1: up to page 262) 234 Definition First step to embed a system into the real world: Transform physical phenomena into electrical signals Usual intention: Transform one dominant phenomenon into one electrical signal e.g. speed, pressure, brightness, loudness, colour, force, humidity, distance, salinity, density, radioactivity, spectrograms, reflectivity, acceleration, conduction, power, turbulence, deformation,,,, or: temperature 2017 Uwe. Zimmer, The Australian National University page 234 of 932 (chapter 1: up to page 262)
235 Measuring temperature Some observable effects of temperature changes: Mean square noise voltage changes Volume changes (gas, liquids, metals) Thermovoltage changes Changes in conductors and semiconductors State changes: into solid, liquid, or gaseous 2017 Uwe. Zimmer, The Australian National University page 235 of 932 (chapter 1: up to page 262) 237 Thermocouple Connect two conductors A and B (of different Seebeck coefficients K A and K B ) on one end. Place the connected end into the temperature zone T 2 which is to be measured. A T 1 U th T 2 B Measure the Voltage over the open ends in temperature zone T 1 : Uth = KA ( T1- T2) + KB ( T2- T1) = ( KA -KB )( T1- T2) T2 = T1- U th ( KA - KB) with T 1 known. 2017 Uwe. Zimmer, The Australian National University page 237 of 932 (chapter 1: up to page 262) 236 Seebeck Coefficient Eth = K$ grad( T), with K being the Seebeck coefficient (material constant of conductors) 0 L T 0 T T L U th 0 L l # # L L U th = 0 E th dl = 0 K$ grad( T) dl = K ( T 0 - T L ) This phenomena stems from the characteristics of electrons to transfer electric potentials as well as to react to heat. 2017 Uwe. Zimmer, The Australian National University page 236 of 932 (chapter 1: up to page 262) 238 Thermocouple Standard thermocouples come prefabricated for different applications: E: Exposed G: Grounded U: Ungrounded A T 1 U th T 2 B Short name Material T max U th with 0cto T max KA - KB (T) Cu-Constantan 400 c C 21.000 mv 42. 5 # 10-6 (J) Fe-Constantan 700 c C 39.720 mv 53. 7 # 10-6 (K) NiCr-Ni 1000 c C 41.310 mv 41. 1 # 10-6 (S) Pth-Pt 13 00 c C 13.138 mv 643. # 10-6 2017 Uwe. Zimmer, The Australian National University page 238 of 932 (chapter 1: up to page 262)
239 Thermocouple Linearity of some standard thermocouples: 90 J-Type: 80 E 70 K-Type: 60 50 40 30 20 10 T K N S B W3 W W5 0 2017 Uwe. Zimmer, The Australian National University page 239 of 932 (chapter 1: up to page 262) 241 Applications of standard thermocouples (TYPE T) Copper-Constantan thermocouples are suitable for subzero temperatures with an upper temperature limit of 371 C and can be used in vacuum, oxidizing, reducing or inert atmospheres. (TYPE ) Platinum 13% hodium - Platinum thermocouples are suitable for continuous use in oxidizing or inert atmospheres at temperatures up to 1482 C. (TYPE S) Platinum 10% hodium - Platinum thermocouples are suitable for continuous use in oxidizing or inert atmospheres at temperatures up to 1482 C. (TYPE B) Platinum 30% hodium - Platinum 6% hodium thermocouples are suitable for continuous use in oxidizing or inert atmospheres and shortterm use in vacuum atmospheres at temperatures up to 1705 C. (TYPE W) Tungsten - henium Alloy thermocouples are used to measure temperatures up to 2760 C. These thermocouples have inherently poor oxidation resistance and should be used in vacuum, hydrogen or inert atmospheres. 2017 Uwe. Zimmer, The Australian National University page 241 of 932 (chapter 1: up to page 262) J 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 U th in mv Temperature in Degrees Celcius 240 Applications of standard thermocouples (TYPE N) Nicrosil-Nisil thermocouples are suitable for use in oxidizing inert or dry reducing atmospheres. Must be protected from sulphurous atmospheres. Very accurate at high temperatures. Virtually the same emf (electromotive force) and range as Type K. (TYPE J) Iron-Constantan thermocouples are suitable for use in vacuum, oxidizing, reducing or inert atmospheres. Suitable for measuring temperatures up to 760 C for largest wire size. (TYPE K) Chromel-Alumel thermocouples are suitable for continuous use in oxidizing or inert atmospheres up to 1260 C for largest wire size. Because their oxidation resistance characteristics are better than those of other base metal thermocouples, they find widest use at temperatures above 538 C. (TYPE E) Chromel-Constantan thermocouples are suitable for use up to 781 C in oxidizing or inert atmospheres for largest gauge wires. Type E thermocouples develop the highest emf per degree of all commonly used thermocouples. 2017 Uwe. Zimmer, The Australian National University page 240 of 932 (chapter 1: up to page 262) 242 Thermocouple Pro: Contra: Accepts high temperature. Small. elatively cheap. equires stable amplifier. Temperature differences only. Cables between the amplifier and the sensor need to be of the same Seebeck coefficient. 2017 Uwe. Zimmer, The Australian National University page 242 of 932 (chapter 1: up to page 262)
243 Measuring temperature (esistors) Thermoresistors Thin film resistor arrays PT100 casings PT 100 resistors are commonly manufactured as (thin film) Platinum wire on / around glass / ceramic tubes / plates. 2017 Uwe. Zimmer, The Australian National University page 243 of 932 (chapter 1: up to page 262) 245 Measuring temperature (esistors) Thermoresistors: Heating & Measuring Assume the PT100 to be potted in a TO18 enclosure: Thermal resistance: th = TPT 100 - TE 480 C P = c V W Assume we want to limit the sensing error to! 0.5 c C around 0c C ( T = 100Ω ): & th U = max TPT 100 - TE 3 P P T U 3 V U T $ & = = & = V th th = 3 T$ T th. 0.323V 2 Thus in order to prevent heating the sensor element by more than 0.5 c C we need to keep the operating voltage under 0.323V. 2017 Uwe. Zimmer, The Australian National University page 245 of 932 (chapter 1: up to page 262) 244 Measuring temperature (esistors) Thermoresistors General case: T = 0[1 + A( T- T0) + B( T- T0) 2 + C ( T- T0 ) + f ] - 3 Platinum: A. 327. # 10 1 K 3 (at 550 c C ) 42. # 10-1 K (at - 150 c C ) PT 100 Calibrated value: 0 c & = 100 Ω! 0.1Ω ; 0.1 Ω &! 0.26 K ange: - 200 ccf + 650 cc esponse time:. 0.1s in flowing water multiple seconds in still air. T 2017 Uwe. Zimmer, The Australian National University page 244 of 932 (chapter 1: up to page 262) 246 Measuring temperature (esistors) Thermoresistors: Connections Separating currents from signals Four wire setup: Vcc Further measures: 2.2 k A Adding a reference resistor. Limit the cable length. Keeping all cables on the same temperatures. Limit the current. Model the non-linearity on the sensor itself. PT100 sensor 100 reference B C D Gnd 2017 Uwe. Zimmer, The Australian National University page 246 of 932 (chapter 1: up to page 262)
247 Thermoresistors Pro: Contra: Potentially higher accuracy. Less non-linearities. Long term stability. Absolute temperature. Limited temperature range ( - 200 ccf + 65 0 cc). Slower reaction time. More expensive. Less robust. Usually bigger. 2017 Uwe. Zimmer, The Australian National University page 247 of 932 (chapter 1: up to page 262) 249 Measuring temperature (Thermistors) Temperature Sensitive Semi-conductors Pro: Contra: Cheap. Can be accurate if combine with compensation for non-linearities. Large effects with temperatures (easy instrumentation). Long term stability (some models). Further limited temperature range ( - 40cCf + 350c C). Strongly non-linear. Comparatively large. Generally instable and inaccurate. 2017 Uwe. Zimmer, The Australian National University page 249 of 932 (chapter 1: up to page 262) 248 Measuring temperature (Thermistors) Temperature Sensitive Semi-conductors ESISTANCE (Ω) NTC: Ω NTC. A $ e Graph with B Graph with B ± B B T PTC: 1000 000 100 000 25 } ( ) 25 C 10 000 } ( ) 25 C + } } TF = ( ) T 1000 b 25 C min 25 C T Temperature ( C) Source: AVX 10 0 25 T min Tb 50 100 150 200 TEMPEATUE ( C) 2017 Uwe. Zimmer, The Australian National University page 248 of 932 (chapter 1: up to page 262) 250 Measuring temperature (Noise Voltage) Noise temperature measurement 2 Based in Nyquist formula: U = 4 kt 3 f Pt10%h-shell d1 d2 sensor Al 2 O 3 99,7% (source: Physikalisch-Technische Bundesanstalt, Berlin) with k: Boltzmann constant, T: thermodynamic temperature, : electric resistance, and 3 f : the measurement bandwidth. 2017 Uwe. Zimmer, The Australian National University page 250 of 932 (chapter 1: up to page 262)
251 Measuring temperature (Noise Voltage) Noise temperature measurement Pro: Contra: Linear. Highly accurate. Long term stability. Wide temperature range: 1 f2500 c K, at! 01.% accuracy over the full range. Expensive. Large. Sophisticated amplification required (small effect). 2017 Uwe. Zimmer, The Australian National University page 251 of 932 (chapter 1: up to page 262) 253 First conclusions we only scratched the surface of conversion methods for one physical value (temperature). Converting physical phenomena into analogue voltages seems to be a complex matter. in fact a whole industry is dedicated to this field exclusively. Always ask for the full sensor specifications (and read them). Never assume that the voltage output is a linear translation of a single physical value. Physical coupling is not the only loss afflicted stage of conversion, yet it is often the most complex one. 2017 Uwe. Zimmer, The Australian National University page 253 of 932 (chapter 1: up to page 262) 252 Further methods of measuring temperature Spreading resistors. Piezos and other temperature sensitive crystals. Temperature controlled current sources (e.g. AD590). Watch Mercury filled thermometers with cameras. Sense blackbody radiation (e.g. infrared-, or more generally: thermal radiation-thermometers) 2017 Uwe. Zimmer, The Australian National University page 252 of 932 (chapter 1: up to page 262) 254 ange and relative speed measurements Some commonly employed principles: Triangulation (optical) Time of flight (optical, acoustical, electro-magnetic) Phase correlation (optical, acoustical, electro-magnetic) Intensity (optical, acoustical) Doppler methods (acoustical, electro-magnetic) Interferometry (optical, electro-magnetic) 2017 Uwe. Zimmer, The Australian National University page 254 of 932 (chapter 1: up to page 262)
255 ange measurements by triangulation Laser d b a CCD line d = b$ tan a non-linear and poor accuracy for d & b Laser required. otherwise simple setup with slow components, often used for liquid level measurements. Measures along the optical axis only problematic for safety applications. 2017 Uwe. Zimmer, The Australian National University page 255 of 932 (chapter 1: up to page 262) 257 ange measurements by time of flight / phase Method: measure the time of flight between the outgoing signal and the received, reflected signal. In case of light, this method requires high resolution timers (> 1 GHz). Method is linear. The achieved resolution depends on the precision of the signal s rising edge and the resolution of employed timers. Signals can be formed and volume measurements are possible. In order to increase the resolution, the outgoing signals are often modulated and the phase shifts between outgoing and reflected signals are detected. 2017 Uwe. Zimmer, The Australian National University page 257 of 932 (chapter 1: up to page 262) 256 ange measurements by triangulation Laser d b CCD line d = b$ tan a non-linear and poor accuracy for d & b Occlusion omits readings not suited for randomly curved surfaces 2017 Uwe. Zimmer, The Australian National University page 256 of 932 (chapter 1: up to page 262) 258 ange and relative speed measurements 2-d Scanning Laser ange Finders Hokuyo UTM-30: 905 nm semiconductor laser. Nominal range: 0.1 30 m outdoors. Maximum range: 60 m Accuracy: 10 50 mm depending on range and background light. Coverage: 270 º. Weight: 210 g. 2017 Uwe. Zimmer, The Australian National University page 258 of 932 (chapter 1: up to page 262)
259 ange and relative speed measurements 2-d Scanning Laser ange Finders SICK (indoor): 905 nm semiconductor laser. Maximum range: 80 m. Accuracy: 5-10 mm (typical). Coverage: 180 º, 0.25 º resolution. esponse time: 53 ms. Weight: 4.5 kg. MTBF: 80,000 h 2017 Uwe. Zimmer, The Australian National University page 259 of 932 (chapter 1: up to page 262) 261 ange and relative speed measurements Ultrasound time-of-flight & Infrared reflected-intensity Classical low end sensors: US signal is transmitted and received on the same membrane. Minimal range limitations. Specular reflections lead to potential overestimation. I intensity readings depend on object material. 2017 Uwe. Zimmer, The Australian National University page 261 of 932 (chapter 1: up to page 262) 260 ange and relative speed measurements 2-d Scanning Laser ange Finders SICK (indoor): 905 nm semiconductor laser. Maximum range: 80 m. Accuracy: 5-10 mm (typical). Coverage: 180 º, 0.25 º resolution. esponse time: 53 ms. Weight: 4.5 kg. MTBF: 80,000 h 100 90 80 70 60 50 40 30 20 10 LMS 211 LMS 221 LMS 291 LMS 211 LMS 221 LMS 291 equired reflectivity [%] over range [m] typ. Neug erät mit Verschm utzung (W arnsignal aktiv) 0 5 10 15 20 25 30 35 40 45 50 Black leather:. 2% reflectivity 55 60 65 70 75 80 (source: SICK AG, Germany) 2017 Uwe. Zimmer, The Australian National University page 260 of 932 (chapter 1: up to page 262) 262 Speed measurements: Doppler current profilers Doppler shift frequency: f 2 f c v d =- s with source frequency fs, relative velocity v and signal speed c. Signal: 250 khz - 3 MHz ange: 160 m, Accuracy:!1% Velocity range:! 10 m s Blanking zone: 0.2-2.0 m 2017 Uwe. Zimmer, The Australian National University page 262 of 932 (chapter 1: up to page 262) 0
263 Summary Physical coupling Physical phenomena Measuring temperature Thermoelements, thermocouples, Thermoresistors, Thermistors, Noise temperature measurement) and many others Measuring range and relative speed Triangulation, Time of flight, Intensity, Doppler methods, Interferometry Examples: Common acoustical and optical sensors 2017 Uwe. Zimmer, The Australian National University page 263 of 932 (chapter 1: up to page 263)