1. Understanding Pressure Sensors
Class 1: The Basics of Specifying
Pressure Sensors
April 7, 2014 Randy Frank

2. Agenda Pressure Sensor Technologies Types of Measurements
Specifying Pressure
Converting Pressure
Pressure Ratings
Example Measurements
Other Issues
Summary

3. Technologies for Measuring Pressure
Bourdon tube
Bellows pressure capsule
Fiberoptic high (combustion) pressure
Linear variable differential transformer (LVDT)
Ceramic capacitive
Stainless steel diaphragm / strain gauge
Piezoelectric
Microelectromechanical Systems (MEMS)
Silicon capacitive
Silicon piezoresistive

4. Silicon Piezoresistive Pressure Sensors
Understanding Smart Sensors

5. Type of Pressure Measurements
Gauge
Absolute
Differential P1 P1 P1
Vacuum
Atmosphere P2
(a)
(b)
(c)
Source:

6. Example Pressure Measurements

7. Gauge Pressure Example
Blood pressure
Disposable invasive blood pressure:

8. Specifying Pressure Pressure is measured in: Torr (mmHg) Inches of Hg
Inches and feet of water
KiloPascals (kPa) and Pascals
PSI (pounds per square inch)
Bar and millibars

9. Converting Pressure

10. Online Pressure Calculators/Conversion

11. Span
Understanding Smart Sensors

12. Effect of Temperature Offset Temperature Shift (0°C-70°C),
Typical: ±0.1 mV
Temperature Effect on Resistance (0°C-70°C), typical: 2800 ppm/°C
Temperature Effect on Span (0°C-70°C),
Typical: ppm/°C
For All Sensors BLVR-L01D

13. Proof Pressure
The level of pressure at which a component, pipe, tube, hose or other fluid passage will not yield during application of internal pressure.

14. Burst Pressure
The maximum pressure that a pressure sensor (diaphragm and/or package) can withstand before failure.

15. Proof and Burst Pressure Example
Standard Pressure Ranges for BLVR-L01D
Operating Range Proof Pressure Burst Pressure
±1 inH2O inH2O 300 inH2O

16. Absolute Pressure Example
An altimeter is an absolute pressure gauge (measurement) that shows height above sea level. The air pressure to height above sea level conversion is frequently performed using a look up table. For example, 10,000 feet above sea level is 10.1 psia (69.7 kPa). Pressure altitude (halt) can be calculated using the equation:
halt = (1-(psta/ )^ )x
Where:
halt is the height in feet
and psta is the pressure in millibars (mb) or hectopascals (hPa)
Look up table:
Equation:

17. Height of a Liquid Column
For a standing liquid, the absolute pressure at a depth H in a liquid is defined as: Pabs = P + (ρ x g x H) Where: Pabs is the absolute pressure at depth H in kg/m-s2 (or Pa) P is the external pressure at the top of the liquid, typically atmospheric pressure for open systems ρ is the density of the fluid (for example, pure water is 1 g/cm3 at 4°C and salt water is g/cm3) g is the acceleration due to gravity (g = 9.81 m/s2) ( ft/s2)) and H is the depth in meters or feet

18. Using Pressure to Measure Flow: A Differential Pressure Example

19. Calculating Flow q = cd π/4 D22 [2(P1 - P2) / ρ(1 - d4) ]1/2 Where:
q is the flow in m3/s
cD is the discharge coefficient, the area ratio = A2 /A1
P1 and P2 are in N/m2
ρ is the fluid density in kg/m3
D2 is the orifice, venturi or nozzle inside diameter (in m)
p1"> D1 is the upstream and downstream pipe diameter (in m)
and d = D2 / D1 diameter ratio

20. Other Issues
Packaging related
Media compatibility

21. Pressure Sensor Connections
All Sensors
Kavlico
PCB Piezotronics
High Pressure Sensors Industrial Products
Pressure connection
Electrical connection

22. Media Compatibility
All Sensors: This series is intended for use with non-corrosive, non-ionic working fluids such as air, dry gases and the like. A protective parylene coating is optionally available for moisture/harsh media protection.
Kavlico: The stainless steel package configurations make them suitable for a broad range of media.
AST: Whether measuring hydraulic pressure in a manifold or corrosive media such as sea water or hydrogen, the AST4000 pressure sensor provides a thick diaphragm to maintain long-term stability and use.

23. Summary Pressure Sensor Technologies Measurements Specifying
Converting
Ratings
Packaging Issues
A successful application considers all of them

24. Topics Later This Week
Tuesday - Sensor Compensation and Signal Conditioning for Piezoresistive Sensors
Wednesday - Case Study: Developing a Smart Pressure Sensor
Thursday - An Introduction to Intelligent Sensor Interfaces
Friday - Sensors in Extreme Applications