1. A General Overview of Sensors
ME 486 Automation
Ryan Palmer
September 28, 2012

2. Overview Definition Important Terms Why are sensors important?
Categories of sensors
Things to be aware of
Example of sensors
Example problem

3. Definition
A sensor is a device that detects physical stimulus and converts it into a signal that can be analyzed for further measurement or interpretation.

4. Important Terms
Accuracy
Repeatability
Resolution
Range
Response time

5. Important Terms
Calibration
Drift
Costs and Reliability
Sensitivity

6. Rise and Fall time definitions
second order system response
(a) Rise-time definition; (b) fall-time definition. Source: J.J. Carr, Sensors and Circuits Prentice Hall.

7. Why are sensors important in automation?
Sensors are used to control the quality and safety of a process by providing important real-time feedback based on physical changes occurring in the process.
Sensors should be found paired with any specification that needs to be monitored for quality or control purposes.

8. Categories of Sensors Acceleration/Vibration Acoustic/Ultrasonic
Chemical/Gas
Electric/Magnetic
Flow
Force/Load/Torque/Strain
Humidity
Leak/Level
Machine Vision
Optical
Motion/Velocity/Displacement
Position/Presence/Proximity
Pressure
Temperature

9. Things to be aware of…
When choosing a sensor be aware specifications specific to the type of sensor (for example photoelectric sensor)
Range –
Distance from the emitter to the receiver
Contrast-
Ratio of light to dark state
Beam Pattern
Graph describing response of sensor to emitter
Excess Gain-
Amount of light falling on a receiver

10. Proximity Sensors Description Selection criteria
Detection sensor able to detect the presence of an object without any physical contact thorough various means. These sensors are very robust and have a long life due to lack of moving parts.
Selection criteria
Distance of target
Velocity of target
Number of targets
Surface of target

11. Proximity Sensors Application Types Conveyor Systems
Vibration measurements
Aviation
Military/Defense
Roller coasters
Types
Inductive (metallic targets)
Capacitive (non – metallic targets)

12. Proximity Sensors Major Manufacturers and Vendors Typical Specs
Omron
C3controls
Rockwell Automation
Eaton
Typical Specs
Response Time
Range
Operating Voltage
Dimensions
Connection Types
Cost range
~$1 - <<$1000

13. Photoelectric Sensors
Description
 a device used to detect the distance, absence, or presence of an object by using a light transmitter, often infrared, and a photoelectric receiver. They are used extensively in industrial manufacturing.

14. Photoelectric Sensors
Application
Manufacturing
Types
Through-Beam (detects target when blocking light)
Reflective (light is emitted and absorbed by same device)
Diffuse (senses light reflected off target)
Background Suppression (controlled range)

15. Photoelectric Sensors
Major Manufacturers and Vendors
Carlo Gavazzi/Electromatic Controls
Eaton Cutler Hammer
Idec
Leuze
Typical Specs
Operating Mode (light and dark)
Range (10mm - 30m)
Response Time (50 μs > )
Accuracy ( +- 10%)
Dimensions (varies)
Cost range
~$10 - $1600

16. Example of Technical Specs
Eaton Cutler Hammer Thru Beam, Comet Series
Unit price $132.20
Specifications
Power type – DC
Max Range – 10 feet
Operating Voltage Range – 10~30 VDC
Output Type – PNP/NPN
Operating Mode – Light/Dark
Connection Type – M8 Micro Connector
Max Load Current – 0.25 Amps
Composition – Non-metallic
Environmental Protection – NEMA 1,2,3,4,4X,6,12,13
Approvals – UL;CUL;CE
H x W x D (in.) – 0.47 x 0.71 x 2.55

17. Response Time Problem
Response Time - is the time between the leading edge of the sensing event and the output’s change of state.
Importance - It helps to determine how long a fast moving object must stay in the sensor’s field of view in order to be detected.
Problem – Calculate the required sensor response time of the production line speed.
Parameters- Packet width = 75 mm
Gap between packets = 25 mm
Process speed = 600 packets/min
Equation -

18. Instrumentation Problem
Solution – 1. Determine the number of packets processed per minute
600 packets/min x (1/60 seconds) = 10 packets/second
2. Determine the distance of linear travel.
75 mm (packet width) + 25 mm (space between) = 100 mm
3. Calculate speed of packet
100 mm/packet x 10 packets/second = 1 m/second
Light Conditions (when object is seen) Dark Conditions (when object is not seen)

19. Questions

20. References Definition of a sensor http://en.wikipedia.org/wiki/Sensor
Important Terms
Pricing and Spec listings  
Classification of sensors    
Technical specs and problem
State of the Art wireless sensors
Problem how sensitive would you need for application