EE 4BD4 Lecture 15 - ece.mcmaster.ca
Transcript of EE 4BD4 Lecture 15 - ece.mcmaster.ca
![Page 1: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/1.jpg)
EE 4BD4 Lecture 15
Strain ( force) Gauges, pressure sensors and Load Cells
1de Bruin EE 4BD4 2017
![Page 2: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/2.jpg)
The Strain Gauge
• Measures the effects of very small displacements (lengthening or shortening) of a resistive sensor
• Is an isometric device with conductor strain gauges having a maximum resistive change of 1 to 3 %
• Resistive change based on both dimensional changes of conductor and strain placed on the sensor (piezoresistive effect)
• Sensors are small, but glued (bonded) to larger structures to increase range of forces measured
2de Bruin EE 4BD4 2017
![Page 3: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/3.jpg)
Basic Theory
3de Bruin EE 4BD4 2017
![Page 4: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/4.jpg)
4de Bruin EE 4BD4 2017
![Page 5: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/5.jpg)
Different Conductive Materials
5de Bruin EE 4BD4 2017
![Page 6: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/6.jpg)
Selection of Type
• Metal foil gauges have a linear resistance change with strain but are less sensitive
• Semiconductor gauges based on piezoresistive effect in germanium and silicon and are much more temperature sensitive
• Resistance change is nonlinear for S‐C strain gauges and are not as commonly used as metal foil
6de Bruin EE 4BD4 2017
![Page 7: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/7.jpg)
7de Bruin EE 4BD4 2017
![Page 8: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/8.jpg)
Types of Foil Strain Gauges
8de Bruin EE 4BD4 2017
![Page 9: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/9.jpg)
Principle of Operation
9de Bruin EE 4BD4 2017
For Nickel only
![Page 10: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/10.jpg)
Measurement Circuits
• Base resistance for bonded gauges between 30 Ω and 3 kΩ (typically 350 Ω)
• R1 R2 and R3 are balancing resistors (e.g. 350 Ω so bridge balanced at 0 strain and V = 0
• Temperature changes cause change in dimensions of structure and gauge and resistivity of gauge resulting in baseline drift
10de Bruin EE 4BD4 2017
![Page 11: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/11.jpg)
• Lead temperauture compensated bridge
• Effects of lead resistance temperature changes
11de Bruin EE 4BD4 2017
![Page 12: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/12.jpg)
Using an Extra Gauge for Temperature Compensation
• Circuit to compensate for temperature effects on structure and gauges
• Fully temperature compensated circuit
12de Bruin EE 4BD4 2017
![Page 13: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/13.jpg)
Beam with Two Gauges
• Beam example
13
• Two stressed gauges
de Bruin EE 4BD4 2017
![Page 14: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/14.jpg)
14de Bruin EE 4BD4 2017
![Page 15: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/15.jpg)
Load Cells
• Force range based on size of load cell structure and beams
• Typical 30 mV output for full load
• If source voltage too high you get excessive heating of resistors
15de Bruin EE 4BD4 2017
![Page 16: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/16.jpg)
16de Bruin EE 4BD4 2017
![Page 17: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/17.jpg)
17de Bruin EE 4BD4 2017
![Page 18: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/18.jpg)
18de Bruin EE 4BD4 2017
![Page 19: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/19.jpg)
19de Bruin EE 4BD4 2017
![Page 20: EE 4BD4 Lecture 15 - ece.mcmaster.ca](https://reader033.fdocuments.in/reader033/viewer/2022041811/625466e2c97b1c05a1009fae/html5/thumbnails/20.jpg)
20de Bruin EE 4BD4 2017