3441 Industrial Instruments 1 Chapter 4 Thermal Sensors Princess Sumaya University 3441 - Industrial Instruments 1 Princess Sumaya Univ. Electronic Engineering Dept. 3441 Industrial Instruments 1 Chapter 4 Thermal Sensors Dr. Bassam Kahhaleh Dr. Bassam Kahhaleh

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Objective Understand how thermal sensors work and how to interface them.

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Metal Resistance Energy bands for solids: Energy gap: required energy for the electron to become free W W W Conduction Conduction Conduction Valence Valence Valence Semiconductors Insulators Metals

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Metal Resistance Nickel Platinum 3 R(25°C) R(T) 2 1 Temperature (°C) −100 0 100 200 300 400 500 600

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Metal Resistance Linear Approximation Quadratic Approximation R2 R1 T1 T T2

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Resistance-Temperature Detectors (RTD) Sensitivity 0: 0.004/°C ~ 0.005 /°C Response Time 0.5 ~ 5 seconds Construction Wire Signal Conditioning Bridge with lead compensation Dissipation Constant (Self-heating)

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors RTD Example 0= 0.005/°C R = 500 Ω at 20°C PD = 30 mW /°C R1 = R2 = 500 Ω VS = 10 V RTD is at 0°C Find R3 R 1 R 2 R 3 VS D RTD a b c

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Thermistors 30 20 Resistance (KΩ) 10 Temperature (°C) −20 0 20 40 60 80 100

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Thermistors Sensitivity ~ 10% /°C Response Time 0.5 ~ 10 seconds Construction Discs, beads, rods … etc Signal Conditioning Divider circuit, Bridge Dissipation Constant (Self-heating)

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Thermistors Example R = 3.5 KΩ at 20°C S = - 10% /°C PD = 5 mW /°C VO = 5 at 20°C Self-heating error? R 1 R TH 10 V V D

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Thermocouples Heat Flow T2 T1 T2 T1 EMF I Seebeck Effect Peltier Effect

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Thermocouples TR + VTC − TM TR

Thermal Sensors Thermocouples Type Material Normal Range J Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Thermocouples Type Material Normal Range J Iron-constantan -190°C to 760°C T Copper-constantan -200°C to 371°C K Chromel-alumel -190°C to 1260°C E Chromel-constantan -100°C to 1260°C S 90%platinum, 10%rhodium-platinum 0°C to 1482°C R 87%platimum, 13%rhodium-platinum

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Thermocouples Type E 50 Type J VTC (mV) 30 Type R 10 Temperature (°C) −200 0 200 400 600 800 1000 1200

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Thermocouples 0 °C Ref. 4 3 20 °C Ref. VTC (mV) 2 1 −20 0 20 40 60 80 Temperature (°C) −1

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Thermocouples Sensitivity Type J: 0.05mV /°C Type R: 0.006mV /°C Response Time 0.01 ~ 20 seconds Construction Welded junction Signal Conditioning High-gain differential amplifier, with high CMRR Reference Compensation (cold junction comp.)

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Thermocouples Cold junction Compensation T K KVTC + Vout Tref VC Temperature Sensor Signal Conditioning

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Bimetal Strips Thermal Expansion γ1 T0 γ2 < γ1 T > T0

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Gas Thermometers Constant Volume: Liquid-Expansion Thermometers

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Solid-State Temperature Sensors ~ 12 mV / K PD = 5 mW / °C At 293 K: VT = 3.516 V I = (5 – 3.516) / 510 = 0.0029 A P = 3.516 * 0.0029 = 10.2 mW ΔT = 10.2 / 5 = 2.04 °C  Increase R 5 V 510 Ω V T T

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Solid-State Temperature Sensors Example J-type TC: ~ 50 μV / °C SS sensor: 8 mV / °C VO = 2 V @ 200 °C VTC (200°C) = 10.78 mV TC Gain = 8 mV / 50 μV = 160 Total Gain = 2000 / 10.78 = 185.5

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Solid-State Temperature Sensors Example −8 mV / °C 10 K 11.59 K SS 320 K − + 2 K T − + 10 K V out 2 K 11.59 K 320 K Tref

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Example Turn-on alarm when T = 10 ± 0.5 °C Turn-off alarm when T ≤ 8 °C RTH = 10 KΩ @ 10 °C = 11 KΩ @ 8 °C Keep self-heating within ± 0.5 °C. Use ± 0.25 °C P = (5 mW / °C)*(0.25 °C) = 1.25 mW @ 10 °C, ITH = 0.354 mA, VTH = 3.5 V Using voltage divider with 5 V supply: R = (5 – 3.5) / 0.354 = 4.28 KΩ @ 10 °C, VD = 1.5 V @ 8 °C, VD = 1.41 V  Hysteresis = 0.09 V

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Example 5 V 500 K R TH 9 K V D + − Vout 5 V 4.28 K 2.327 K Vref = 1.5 V 1 K

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Example Measured T = 50 °C ~ 80 °C (error ≤ ± 1 °C) VO = 0 ~ 2 V RTD: R(65°C) = 150 Ω (65°C) = 0.004 / °C PD = 30 mW / °C R(50°C) = 150 [ 1 + 0.004 (50 – 65) ] = 141 Ω R(80°C) = 150 [ 1 + 0.004 (80 – 65) ] = 159 Ω Keep self-heating within ± 1 °C P = (30 mW / °C)*(1 °C) = 30 mW @ 80 °C, IRTD = 13.7 mA, VRTD = 2.17 V

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Example 5 V 10 K 220 220 10 K − + + − V out 10 K 141 RTD 10 K 138 K 10 K @ 50 °C: RRTD = 141 Ω, ΔV = 0, Vout = 0 @ 80 °C: RRTD = 159 Ω, ΔV = 0.1447 V, Vout = 0.1447 * 13.8 = 2 V

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Example Measured T = 500 ~ 600 °F (260 °C ~ 315.6 °C) VO = 0 ~ 5 V J-type TC: Tref = 25 °C VTC(260 °C) = 12.84 mV VTC(315.6 °C) = 15.9 mV Vout = m VTC + V0 0 = m(0.01284) + V0 5 = m(0.01590) + V0 m = 1634, V0 = − 21, Use Gain = 100 * 16.34

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors Example 5 V 2.88 K Vref = 1.289 V 10 K 1 K 100 K 163.4 K 1 K T − + 10 K − + 1 K V out 100 K Tref = 25 °C

3441 - Industrial Instruments 1 Princess Sumaya University 3441 - Industrial Instruments 1 Thermal Sensors End of Chapter 4