Temp Measurement
Project
1
Project: Temperature Measurement
• Write a single VI that measures thermistor, AD590 IC, and thermocouple temperatures
• Thermistor: Epcos Model B57863S0103F040
◦ Nominal 10 kW resistance (@ 25°C)
◦ R-T Data file: B57863S0103F40_C-Ohm.txt
• AD590HK Integrated Circuit (IC) Temperature Transducer
◦ PTAT current regulator (Proportional To Absolute Temperature)
◦ 1 µA/K
◦ AD590 datasheet
• Type “T” Thermocouple
◦ Part # 5TC-GG-T-24-36 Thermocouple Datasheet
◦ Thermocouple Accuracy
◦ Omega Accuracy & Color chart
◦ “Special Limits of Error”
2
Thermocouples - Background
• Floating Signal Voltage Source
◦ Seebeck effect
◦ Dissimilar metals junction
◦ Proportional to Temperature difference
• Differential measurement mode
◦ µV levels
◦ Common mode noise cancellation
• Need a reference temperature to measure
◦ Assume the breadboard is your isothermal block
◦ Use IC Transducer or Thermistor
3
T-type Thermocouple and Tref
=
Law of
Intermediate
Metals
USE A KNOWN TEMPERATURE
(MELTING ICE)
Cu
KNOWN REFERENCE
TEMPERATURE
4
Thermistor & IC Hardware Circuits
• Use the built-in +5 V of the USB-6211 to
power the circuits
◦ VR to determine current i
◦ Vth/i to get Rth
+5V
10 kΩ
Precision
Resistor
• AD590 IC transducer factory set 1 µA/K @
approx. 25°C (298 K)
◦ Trim to 1 mV/K (953 Ohm + 100 Ohm Trimpot)
◦ Calibrate with Thermistor
VR
Thermistor
Vth
5
Hardware
• USB-6211 DAQ
Resistors
• Solderless breadboard
Solderless
Breadboard
• Epcos Thermistor
• IC Transducer: AD590KH
Thermistor
• Thermocouple (not shown)
• Resistors
◦ 0.1%: 1 kOhm, 10 kOhm
◦ 1% 953 Ohm
USB-6211
AD590KH
• Jumper Wire Kit
• Breadboard-DAQ connecting wires (in DAQ
box)
100 Ω trimpot
6
Resistors
Resistor
Band
1
2
3
4
5
390 Ω
3
9
0
x1
± 0.1%
953 Ω
9
5
3
x1
± 1%
1.00 kΩ
1
0
0
x10
± 0.1%
10.00 kΩ
1
0
0
x100 ± 0.1%
49.90 kΩ
4
9
9
x100
± 1%
7
Wiring/Jumper Connections
• Clear breadboard
◦ Silver = connected
◦ White = not connected
A thru E & F thru J
Each row 1 to 63
Trimpot top, bottom, pins
• AD590KH (bottom view)
AD590KH
“+” and “-”
Entire column
8
Thermistor Temp vs. Resistance
• Steinhart-Hart
•
1
𝑇𝑇
= 𝐴𝐴 + 𝐵𝐵𝐵𝐵𝐵𝐵 𝑅𝑅 + 𝐶𝐶𝑙𝑙𝑙𝑙 𝑅𝑅
• Curve Fitting Express VI
3
• General least squares linear
◦
◦
◦
◦
Models 1, x, x^3
Locations: X is 1/T
Signals: Y is ln(R)
a0, a1, a2 are A, B, C respectively
9
Useful Functions & Sub-VIs
• Functions >> Express >> Curve Fitting
• Functions >> Programming >> File I/O
◦ Read Delimited Spreadsheet.vi
◦ Write Delimited Spreadsheet.vi
◦ Delimiters
◦ Tab (“tab-delimited text”)
◦ Comma (CSV; “Comma Separated Values”)
• Functions >> Programming >> Numeric >>
Scaling
◦ Convert Thermistor Reading.vi
◦ Convert Thermocouple Reading.vi
◦ Temperature to Volts.vi
◦ Volts to Temperature.vi
10
Uncertainty - Thermistor
• Measure 2 voltages; calculate R:
• Temperature:
• where: 𝑅𝑅𝑡𝑡𝑡 =
1
𝑇𝑇𝑡𝑡𝑡
𝑉𝑉𝑡𝑡𝑡
𝑖𝑖𝑡𝑡𝑡
= 𝐴𝐴 + 𝐵𝐵𝐵𝐵𝐵𝐵 𝑅𝑅𝑡𝑡𝑡 + 𝐶𝐶𝐶𝐶𝐶𝐶 𝑅𝑅𝑡𝑡𝑡
=
𝑉𝑉𝑡𝑡𝑡
𝑉𝑉𝑅𝑅
𝑅𝑅𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
• Sources of Uncertainty
◦
◦
◦
◦
=
𝑉𝑉𝑡𝑡𝑡 𝑅𝑅𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
3
+5V
𝑉𝑉𝑅𝑅
• 𝑇𝑇𝑡𝑡𝑡 = 𝐴𝐴 + 𝐵𝐵𝐵𝐵𝐵𝐵
• 𝑢𝑢 𝑇𝑇𝑇𝑇𝑇 =
𝑉𝑉𝑅𝑅
𝑑𝑑𝑇𝑇𝑡𝑡𝑡 2
𝑢𝑢𝐷𝐷𝐷𝐷𝐷𝐷 2
𝑑𝑑𝑉𝑉𝑅𝑅
+
VR
Thermistor
Vr (precision & accuracy)
Vth (precision & accuracy)
Resistor uncertainty (0.1%)
Thermistor uncertainty
𝑉𝑉𝑡𝑡𝑡 𝑅𝑅𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
10 kΩ
Precision
Resistor
Vth
+ 𝐶𝐶𝐶𝐶𝐶𝐶
−1
𝑉𝑉𝑡𝑡𝑡 𝑅𝑅𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 3
𝑑𝑑𝑇𝑇𝑡𝑡𝑡 2
𝑢𝑢𝐷𝐷𝐷𝐷𝐷𝐷 2
𝑑𝑑𝑉𝑉𝑡𝑡𝑡
𝑉𝑉𝑅𝑅
+
𝑑𝑑𝑇𝑇𝑡𝑡𝑡 2
𝑢𝑢𝑅𝑅 2
𝑑𝑑𝑅𝑅𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
1
+
𝑑𝑑𝑇𝑇𝑡𝑡𝑡 2
𝑢𝑢𝑡𝑡𝑡 2
𝑑𝑑𝑇𝑇𝑡𝑡𝑡
Range
± 10 V
±5V
±1V
± 200 mV
Resolution
[µV]
320
160
32
6.4
Absolute Accuracy @
Full Scale [µV]
2690
1410
310
88
11
Uncertainty - Thermocouple
• Measure
• Uncertainty Percent Contribution (UPC)
◦ Voltage
◦ Reference Temp
◦ 𝑈𝑈𝑈𝑈𝑈𝑈𝐷𝐷𝐷𝐷𝐷𝐷 =
• Sources of Uncertainty
◦ 𝑈𝑈𝑈𝑈𝑈𝑈𝑇𝑇_𝑅𝑅𝑅𝑅𝑅𝑅 =
◦ Vtc (precision & accuracy)
◦ Tref (precision & accuracy)
◦ Thermocouple wire
◦ 𝑈𝑈𝑈𝑈𝑈𝑈𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 =
◦ Check: 𝑈𝑈𝑈𝑈𝑈𝑈𝐷𝐷𝐷𝐷𝐷𝐷 + 𝑈𝑈𝑈𝑈𝑈𝑈𝑇𝑇_𝑅𝑅𝑅𝑅𝑅𝑅 + 𝑈𝑈𝑈𝑈𝑈𝑈𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 = 1
• NIST Thermocouple Coefficients
𝑖𝑖
◦ 𝑉𝑉𝑅𝑅𝑅𝑅𝑅𝑅 = ∑8𝑖𝑖=0 𝑐𝑐𝑇𝑇𝑇𝑇,𝑖𝑖 𝑇𝑇𝑅𝑅𝑅𝑅𝑅𝑅
◦ 𝑇𝑇𝑡𝑡𝑡𝑡 = ∑6𝑖𝑖=0 𝑐𝑐𝑉𝑉𝑇𝑇,𝑖𝑖 𝑉𝑉𝑣𝑣𝑣𝑣 + 𝑉𝑉𝑅𝑅𝑅𝑅𝑅𝑅
• 𝑢𝑢 𝑇𝑇𝑇𝑇𝑇𝑇 =
𝑑𝑑𝑇𝑇𝑡𝑡𝑐𝑐 2
𝑢𝑢𝐷𝐷𝐷𝐷𝐷𝐷 2
𝑑𝑑𝑉𝑉𝑣𝑣𝑣𝑣
+
𝑑𝑑𝑇𝑇𝑡𝑡𝑡𝑡 2
2
𝑢𝑢
𝑑𝑑𝑉𝑉𝑡𝑡𝑡𝑡 𝐷𝐷𝐷𝐷𝐷𝐷
𝑢𝑢𝑇𝑇𝑇𝑇𝑇𝑇 2
𝑑𝑑𝑇𝑇𝑡𝑡𝑡𝑡 2
2
𝑢𝑢
𝑑𝑑𝑇𝑇𝑅𝑅𝑅𝑅𝑅𝑅 𝑇𝑇_𝑅𝑅𝑅𝑅𝑅𝑅
𝑢𝑢𝑇𝑇𝑇𝑇𝑇𝑇 2
𝑢𝑢𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 2
𝑢𝑢𝑇𝑇𝑇𝑇𝑇𝑇 2
𝑖𝑖
𝑑𝑑𝑇𝑇𝑡𝑡𝑐𝑐 2
𝑢𝑢 𝑇𝑇_𝑅𝑅𝑅𝑅𝑅𝑅 2
𝑑𝑑𝑇𝑇𝑅𝑅𝑅𝑅𝑅𝑅
1
+
𝑑𝑑𝑇𝑇𝑡𝑡𝑐𝑐 2
𝑢𝑢𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 2
𝑑𝑑𝑇𝑇𝑡𝑡𝑡𝑡
12
References
1) Alciatore, David. Introduction to Mechatronics and Measurement Systems. McGraw-Hill
Higher Education. Kindle Edition.
2) https://www.ni.com/getting-started/labview-basics/ (accessed 1/10/22)
3) NI USB-621x Specifications (Document 371932F-01, April 2009)
4) NI USB-621x User Manual (Document 371931F-01, April 2009)
5) Omega Engineering, Practical Temperature Measurement, p Z-19 to Z-40.
6) Cengel, Y. A. & Cimbala, J. M. (2018). Fluid Mechanics: Fundamentals and Applications (4th
ed.). McGraw-Hill.
7) Holman, J. P. (2001). Experimental Methods for Engineers; (7th ed); McGraw-Hill.
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