Measurements & Instrumentation

Transcription

1 Measurements & Instrumentation PREPARED BY Academic Services Unit August 2013 Institute of Applied Technology, 2013

2 Module Objectives Upon successful completion of this module, students should be able to: 1. Demonstrate understanding of the importance of sensors and the function of proximity sensors. 2. Identify types of proximity sensors and their applications. 3. Demonstrate understanding of proximity sensor applications through experiments. Module Contents: Topic Page No. 4.1 Introduction to Proximity Sensors Proximity Sensor Applications Lab Activity Lab Activity Review Exercise Assignment 16 2

3 4.1 Introduction to Proximity Sensors ATE 314 Measurements & Instrumentation Sensors have increasingly become important components used to acquire and transmit information in automated production systems. They are also used in a number of other real world applications. Sensors can be divided, according to the type of output signal, into binary sensors, also called switches, and analog sensors. Binary sensors produce a digital output ( high or low ), and analog sensors provide a varying or analog output. Sensors are devices which can operate both by means of contact, or without contact; they are selected based on the requirement of the application. For example, the door at the entrance of the mall is equipped with an ultrasonic sensor that senses the presence of people and enables the door to open and close automatically (See Figure 4.1). Figure 4.1: Sensor Application Example In this module, you will learn about proximity sensors. Proximity sensors detect whether or not an object is located or present at a certain position. Sensors of this type operate electronically without contact. Several advantages of contactless proximity sensors are given below: Precise and automatic sensing of position. Contactless sensing protects objects from damage. Fast response, and do not include moving parts which can wear out. 3

4 4.2 Proximity Sensor Applications Different types of proximity sensors are used in many areas of the industry, based on the application of position detection. In this module, the following types of proximity sensors will be covered: 1. Ultrasonic Sensor 2. Optical sensor 3. Inductive sensor 4. Capacitive sensor 4

5 Ultrasonic sensors can detect solid, liquid, granular and powdery substances; they are used in applications where it is required to detect the object within a specified range. For example, an Ultrasonic sensor that is embedded in the front and/or rear bumpers of the car, helps to measure the distances to nearby objects at a low level. This provides feedback/warning to the driver regarding the obstacle in the form of an alarm, and thereby helps in preventing accidents. Figure 4.2: Ultrasonic Sensor in Car Other applications involve detecting the presence of a person and opening a door, or, detecting the presence of a car in a car wash station. Figure 4.3: Detecting a person Figure 4.4: Detecting a car at car wash The figures below list the ultrasonic sensor applications in industrial production and material handing processes: Figure 4.5: Sensing Liquid Levels Figure 4.6: Control of lifting vehicles 5

6 Optical proximity sensors are used for counting boxes, breakage and jam detection etc. Inductive proximity sensors are used to detect the presence of metals while Capacitive proximity sensors are used to detect metal and even non-metallic objects such as wood, paper, liquid and so on. However, the detection range of inductive and capacitive proximity sensors is very small. Counting Application: Different types of proximity sensors are used to count the number of items produced in production lines based on the material used in the application, as shown in the Figure 4.7 below. Counting Cartons Bottle Counting Counting IC Chip Pins Counting Packages Figure 4.7: Counting Application Examples Conduct Lab Activity 1 6

7 Detecting the presence of materials Detecting the presence of materials/objects is very important in automation industries. Detecting Milk in cartons Figure 4.8: Capacitive Sensor Application Detecting Metallic Caps Figure 4.9: Inductive Sensor Application Conduct Lab Activity 2 on Page 11 7

8 4.3 Lab Activity 1 Objective: To perform the counting application using an optical proximity sensor. Materials: 1. Power supply 24 VDC 2. Counting Unit 3. Multimeter, 4. Boxes/ bottles/any other items to be counted 5. Optical sensor unit (Festo: ) Procedure: 1. Connect the 24 V socket of the power supply to the 24 V socket of the counting unit and the RED wire of the optical sensor 2. Connect the 0 V socket of the power supply to the zero socket of the counting unit and the BLUE wire of the Optical sensor 3. Connect the WHITE wire of the optical sensor to the clock socket of the counting unit 4. Set the multimeter to measure voltage. Connect the COM probe of the multimeter to the BLUE wire of the sensor and the red probe of the multimeter to the WHITE wire of the optical sensor. 8

9 5. The following table summarizes the connections. Power Supply Counting Unit Sensor wires Multimeter 24 V 24 V Red wire - 0 V 0 V Blue wire COM Probe (Black) - Clock socket White wire Voltage Probe (RED) 6. Ensure that the toggle switch (No. 1) on the counting unit is set to Imp. 7. Press start on the counting unit No Description 1 Display Mode Switch Start push button and 2 socket 3 Stop push button and socket 4 Clock socket 5 6 Voltage supply (+24 VDC) Digital display with four digits 7 Reset push button and socket 8 Voltage supply 0 VDC 9 Pulse output 100 pulses/s 10 Pulse output 1000 pulses/s 8. Measure the voltage output of the sensor before detecting any object. Record your reading in Table

10 9. Move the bottle near the optical sensor. What do you notice on the counting unit display? 10. Measure the voltage output of the sensor after detecting the first bottle. Record your readings in Table 4.1. Sensor output Voltage (before detecting the object) Sensor output Voltage (once the object is detected) Table Move another bottle near the optical sensor and continue the procedure. Inference: What do you understand from this experiment? List an application where you think the optical sensor would be useful. 10

11 4.4 Lab Activity 2 Objectives: To detect objects within a certain range using the ultrasonic proximity sensor. Material: 1. Power supply 24 VDC 2. Analog Ultrasonic sensor unit (Festo: ) 3. Multimeter 4. Object under test Procedure: 1. Connect the following circuit: 2. Set the Multimeter to measure current. 11

12 3. Move the object until it touches the sensor. Record the multimeter current reading in Table Move the object 1 cm from the sensor and record the multimeter reading in Table Repeat step 4 until the multimeter reading becomes constant (the sensor cannot detect the object anymore) Distance (cm) Sensor Output Reading (ma) Table

13 Plot the characteristic curve of the sensor. calculate the sensitivity of the curve. Inference: What do you think is the range of the given ultrasonic sensor? Justify your answer. 13

14 4.5 Review Exercise 1. What is the function of a proximity sensor? 2. What are the advantages of proximity sensors? 3. Mention three applications of proximity sensors: Indicate the proximity sensor that could be used in the following application: Detecting Metallic caps 14

15 5. Write one difference between inductive and capacitive proximity sensors Inductive sensor Capacitive sensor 6. Describe the sensor application in the following pictures: Picture Application 15

16 4.6 Assignment Visit your classroom blog that has been created by your instructor, and complete the following two tasks: Task-1: Sensor Application at your School Identify one proximity sensor application at your school, and post your views in the form of a message under the following questions in your classroom blog: 1. Explain the sensor application to your peers 2. Share your thoughts on why you think this technology is helping your school. Task-2: Proximity sensors in your car Identify two different types of proximity sensors that are used in your car and post your views in the form of a message under the following questions in your classroom blog: 1. Explain the first sensor application to your peers, and post your views on why you think it is useful. 2. Explain the second sensor application to your peers, and post your views on why you think it is useful. 3. Share your views on how you could improve this technology by using additional sensors to make your car hi-tech! 16

17 Notes 17