1 Selection of the sensors and types of sensors.pptx

how to select a right system this is a base document o learn

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2. What is Sensor ? Process of Selecti ng a Right Sensor Environmental Conditions for Sensor Example 3 Questions to Guide You in Choosing the Right Sensor

3. What is Sensor ? A D evice that detects and responds to some type of input from the physical environment. It converts signals from one energy domain to electrical domain.

4. Difference between Sensor & Transducer T ransducer converts the physical quantity or nonelectrical into another signal or electrical signal.

5. Sensor Examples

6. Output of Sensor Voltage DC (From µvolts to 100’s of volts) AC (Sine, pulse, varying amplitude, duty cycle, phase and frequency) Current From mA to A Resistance Frequency Modulation

7. Different phenomena to help you choose the best option for your application Temperature Strain Sound Vibration Position and Displacement Pressure Force Humidity

8. Temperature Sensors Thermocouples: Thermocouples are effective in applications that require a large temperature range ( -210 ° C to 1760 ° C). They are inexpensive ($1 to $50 USD) and have a response time of fractions of a second.

9. Temperature Sensors RTD : In contrast to thermocouples, RTDs have a smaller temperature range (-200 ° C to 500 °C) R equire current excitation, and have a slower response time (2.5 to 10 s). RTDs are primarily used for accurate temperature measurements (±1.9 percent) in applications that are not time critical. RTDs can cost between $25 and $1,000 USD.

10. Temperature Sensors Thermistors: Thermistors have a smaller temperature range (-90 to 130 °C). They have the best accuracy (±.05 °C). Thermistors involve excitation like the RTD; however, the thermistor requires voltage excitation rather than current excitation. A Thermistor typically ranges between $2 and $10 USD in price.

11. Comparison of Temperature Sensor

12. Understand the measurement application and requirements. How quickly will the temperature change? Determine an appropriate Response time . How much Accuracy is required? Consider the impact of sensor accuracy on overall measurement accuracy. Determine the temperature ranges that you must measure. Select a sensor type that operates beyond the Full range of possible temperatures. select the type with the most Linear response over your range of interest to improve voltage- or resistance-to-temperature conversion accuracy. Steps for Selecting Temperature Sensor

13. Consider the environment in which we are deploying the sensors. Pick a suitable material to resist any chemical exposure. Determine if you need isolation to prevent ground loops/noise. Make sure your sensors are rated to withstand vibration or abrasion if you are exposing them to those. Consider how you are mounting your sensors and select an appropriate mounting style to maximize the thermal connection. Cost Steps for Selecting Temperature Sensor

14. Temperature Sensors RTD : In contrast to thermocouples, RTDs have a smaller temperature range (-200 to 500 °C), require current excitation, and have a slower response time (2.5 to 10 s). RTDs are primarily used for accurate temperature measurements (±1.9 percent) in applications that are not time critical. RTDs can cost between $25 and $1,000 USD.

15. Thermistors: Thermistors have a smaller temperature range (-90 to 130 °C). They have the best accuracy (±.05 °C). Thermistors involve excitation like the RTD; however, the thermistor requires voltage excitation rather than current excitation. A Thermistor typically ranges between $2 and $10 USD in price. Temperature

16. It is a ratio of the change in length of a material to the original, unaffected length. Strain is typically measured by a resistive strain gage. Flat resistors are usually attached to a surface that is expected to flex or bend. F our different types of strain are A xial, B ending, S hear, and torsional. Strain

17. Axial strain measures how a material stretches or compresses as a result of a linear force in the longitudinal axis of the specimen . Axial strain is defined as extension per unit length. Axial Strain = extension / original Length Axial Strain

18. Bending strain measures a stretch on one side of a material and the contraction on the opposite side due to the linear force applied in the vertical direction. Using the line segment, AB, the before and after length can be used to give Bending Strain

19. Shear strain measures the amount of deformation that occurs from a linear force with components in both the horizontal and vertical directions. It can be defined as the change in right angle or t he angle of deformation is then termed as the shear strain. It is measured in radians Shear Strain

20. Torsional strain measures a circular force with components in both the vertical and horizontal directions. When a torque is applied to the structure, it will twist along the long axis of the rod, and its cross section remains circular. Torsional Strain

21. You can use up to four active strain gages to build a Wheatstone bridge circuit; this is called a full-bridge configuration. There are also half-bridge (two active strain gages) and quarter-bridge (one active strain gage) configurations. The more active strain gages you use, the more accurate your readings will be . Strain Measurement

22. Strain

23. How to choose the right strain gage? Measurement Type Quarter Bridge Half-Bridge Full-Bridge Type I Type II Type I Type II Type I Type II Type III Axial Strain Yes Yes Yes No No No Yes Bending Strain Yes Yes Yes Yes Yes Yes No Compensation Transverse Sensitivity No No Yes No No Yes Yes Temperature No Yes Yes Yes Yes Yes Yes Sensitivity Sensitivity at 1000 µε ~0.5 mV/V ~0.5 mV/V ~0.65 mV/V ~1.0 mV/V ~2.0 mV/V ~1.3 mV/V ~1.3 mV/V Installation Number of Bonded Gages 1 1* 2 2 4 4 4 Mounting Location Single Side Single Side Single Side Opposite Sides Opposite Sides Opposite Sides Opposite Sides Number of Wires 2 or 3 3 3 3 4 4 4 Bridge Completion Resistors 3 2 2 2

24. Sound

25. Vibration Vibration is the movement or mechanical oscillation about an equilibrium position of a machine or component. It can be periodic, such as the motion of a pendulum, or random, such as the movement of a tire on a gravel road. It can be expressed in metric units (m/s ² ) or units of gravitational constant “g,” where 1 g = 9.81 m/s ² .

26. How to measure vibration? Vibration is most commonly measured using a ceramic piezoelectric sensor or accelerometer. Accelerometer is a sensor that measures the dynamic acceleration of a physical device as a voltage. These versatile sensors can also be used in shock measurements (explosions and failure tests) and slower, low-frequency vibration measurements.

27. Vibration

28. How do I choose the right accelerometer? Vibration Amplitude: The maximum amplitude or range of the vibration you are measuring determines the sensor range that you can use. Sensitivity: It describes the conversion between vibration and voltage at a reference frequency. Sensitivity is specified in mV per G. Use a low sensitivity accelerometer to measure high amplitude signals and a high sensitivity accelerometer to measure low amplitude signals. Number of Axes: You can choose from two axial types of accelerometers. It can be single or Triaxial. Weight: Accelerometers should weigh significantly less than the structure you are monitoring. Adding mass to the structure can alter its vibrational characteristics and potentially lead to inaccurate data and analysis.

29. How do I choose the right accelerometer? Mounting Options: You can choose from four typical mounting methods: Handheld or probe tips Magnetic Adhesive Stud mount Method Frequency Limit Handheld 500 Hz Magnetic 2,000 Hz Adhesive 2,500 to 5,000 Hz Stud > 6,000 Hz

30. How do I choose the right accelerometer? Environmental Constraints: Pay attention to critical environmental parameters such as maximum operating temperature, exposure to harmful chemicals, and humidity. Cost: Although charge mode and IEPE accelerometers have similar costs, IEPE accelerometers have a significantly lower cost for larger, multichannel systems because they do not require special low-noise cables and charge amplifiers.

31. Position & Displacement Hall effect Sensors Potentiometers Optical Encoders – Linear and Rotary Linear and Rotary Variable DifferentialTransformers Eddy-Current Proximity Probe Reflective Light Proximity Sensor

32. Position & Displacement : Hall Effect Sensors It's a device that is used to measure the magnitude of a magnetic field. Its output voltage is directly proportional to the magnetic field strength through it. Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing , tachometers and anti-lock braking systems

33. Position & Displacement : Potentiometer It's is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider.

34. Position & Displacement : Encoders

35. Position & Displacement : Linear and Rotary Variable DifferentialTransformers LVDT and RVDT use magnetic induction to determine position. effective for industrial and aerospace applications because of their robustness . Both require signal conditioning , which can add to cost.

36. Position & Displacement : Eddy-Current Proximity Probe It use magnetic fields to determine position and are moderately priced. used less in applications that require highly detailed positioning information Used in assembly lines when mounted on a reasonably stationary mechanical structure to measure nearby moving machinery or products

37. Position & Displacement : Reflective Light Proximity Sensors It use a beam’s travel time to and from a reflective target to determine distance. Quick response time and are excellent in applications where large gaps exist between the sensor and target. Line of sight is required when using this sensor.

38. Position & Displacement

39. Pressure

40. Force

41. Process of selecting the right sensor 1) Type of Sensing 2) Composition of Target 3) Distance to Target  4) Form Factor 5) Control Interface 6) Special Requirements 7) Electrical Connection

42. Process of selecting the right sensor Type of Sensing Am I sensing a process parameter (e.g. temperature, pressure, flow), the presence of an object, the distance to a target, or the position of a mechanism?  Let’s say I want to detect the presence of an object.  That means I am looking for some kind of proximity sensor (sometimes called “presence sensors” or “object detection sensors”).  There are several kinds of sensor technologies that can detect the presence (or absence) of an object.  Inductive, photoelectric, capacitive, magnetic, and ultrasonic sensors are all possible candidates at this stage of the selection process.

43. Process of selecting the right sensor 2) Composition of Target   What is the material composition of the object (metallic, non-metallic, solid, liquid, granular)?  Let’s say the object is metallic.  Inductive, photoelectric, capacitive, and ultrasonic sensors are all capable of detecting metallic objects.

44. 3) Distance to Target How far away from the object must the sensor be?  Well, if I am building a compact piece of automation machinery, I want to keep everything as close together as possible.   I expect the sensor to be installed pretty close to the metallic object that I want to detect.  In this case, an inductive proximity sensor would be the best choice.  Although inductive sensors have rather short sensing distances (typically 1mm up to about 50mm) compared to other sensing technologies. Let’s say that I have decided the sensor needs to see the metallic target at a distance of 4mm. Process of selecting the right sensor

45. 4) Form Factor What sort of physical form-factor best fits my application?  In our example, it’s fairly tight space and there isn’t much room to mount something with a lot of length to it.  That eliminates the most common inductive proximity sensor type.  We’re going to be looking at some kind of low-profile, flat sensor, typically called a block style or rectangular type. Process of selecting the right sensor

46. 5) Control Interface What kind of controller interface and switching logic is required?  These days, most sensors are 3-wire DC types.  There are other types out there, such as 2-wire DC and 2-wire AC/DC, but by far the vast majority of control systems will require a 3-wire DC sensor.  In our case, we need a “3-wire PNP N.O. sensor,” meaning 3 wires (+24DC, 0VDC, and output), a PNP-type “sourcing” output (current is sourced from the sensor to the controller), and “normally open” switching logic (means the output is “off” when the sensor does not see the target). Process of selecting the right sensor

47. 6) Special Requirements Are there any special application requirements?  Special application requirements. That might be things like high temperatures (more than 80 degrees C),  nearby welding processes. Process of selecting the right sensor

48. 7) Electrical Connection How do I want to make the electrical connection?  Sensors are typically available with three kinds of electrical connections:  a) pre-wired cable with flying leads b) integrated quick-disconnect connector c) a pre-wired cable with a molded -on connector (often called a “pigtail” connector). Process of selecting the right sensor

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