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

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

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.

Important Terms Accuracy Repeatability Resolution Range Response time

Important Terms Calibration Drift Costs and Reliability Sensitivity

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.

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.

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

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

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

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

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

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.

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)

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

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

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 -

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)

Questions

References Definition of a sensor http://en.wikipedia.org/wiki/Sensor Important Terms http://zone.ni.com/devzone/cda/ph/p/id/227 Pricing and Spec listings   http://www.galco.com/shop Classification of sensors  http://www.fas.org/irp/imint/docs/rst/Intro/Part2_5a.html  http://tec.upc.es/ie/transp_2010-11/white87.pdf Technical specs and problem http://www.galco.com/get/Photoelectric http://info.bannerengineering.com/xpedio/groups/public/documents/literature/120236.pdf State of the Art wireless sensors http://www.frost.com/sublib/display-pressrelease.do?Src=RSS&id=262358687 Problem how sensitive would you need for application http://en.wikipedia.org/wiki/Tiltmeter