Input - Output Devices for PLC

Input - Output Devices for PLC, adopted from Programmable Logic controller by W. Bolton

1. 1 Presentation on Input – Output Devices used with PLC Presented By: Name: Arko Saha Roll: 138014 Department of Mechatronics Engineering Ra jshahi University of Engineering & Technology Course No. : MTE 4101 Course Name : Automation

2. 2 PLC Structure Input Central Processing Unit Output

3. 3 PLC Structure Input Central Processing Unit Output

4. 4 I/O Module The I/O interface section of a PLC connects it to external field devices. The main purpose of the I/O interface is to condition the various signals received from or sent to the external input and output devices. Input modules converts signals from discrete or analog input devices to logic levels acceptable to PLC’s processor. Output modules converts signal from the processor to levels capable of driving the connected discrete or analog output devices. O : 2 / 00 Input Module Number Terminal Number Output Module Number Terminal Number I : 1 / 00

5. 5 Sensors which give digital/discrete, i.e. on/off signal to the input ports of the PLC. Accuracy Range Respon se Time Rise Time Sensiti vity Stability Repeatability Reliability Input Devices

6. 6 Mechanical Switch: A mechanical switch generates an on−off signal or signals as a result of some mechanical input causing the switch to open or close. Input Devices Switches are available with normally open (NO) or normally closed (NC) contacts. NO switch has its contacts open in the absence of a mechanical input and the mechanical input is used to close the switch. NC switch has its contacts closed in the absence of a mechanical input and the mechanical input is used to open the switch.

7. 7 Input Devices Limit Switch: A switch which is used to detect the presence or passage of a moving part. It can be actuated by a cam, roller or lever.

8. 8 Input Devices Proximity switches: Proximity switches are used to detect the presence of an object without making contact with it. There are a number of forms of such switches, some being only suitable for metallic objects. Eddy Current type: It has a coil which is energized by a constant alternating current and produces a constant alternating magnetic field. When a metallic object is close to it, eddy currents are induced in it. The magnetic field due to these eddy currents induces an e.m.f . back in the coil with the result that the voltage amplitude needed to maintain the constant coil current changes. The voltage amplitude is thus a measure of the proximity of metallic objects.

9. 9 Reed switch: Consists of 2 overlapping, but not touching strips of a springy ferromagnetic material sealed in glass or plastic casing. When the magnet is brought close to the switch, the strips become magnetized and are attracted to each other, causing the contacts to close. C apacitive proximity switch: A proximity switch that can be used with metallic and non-metallic objects. The sensor of the capacitive proximity switch is just one of the plates of the capacitor, the other plate being the metal object whose proximity is to be detected. Thus the proximity of the object is detected by a change in capacitance. Input Devices

10. 10 Inductive proximity switch: Consists of a coil wound round a ferrous metallic core. When one end of this core is placed near to a ferrous metal object there is effectively a change in the mount of metallic core associated with the coil and so its inductance changes. Inductance change can be measured by resonant circuit and can be made to activate a switching circuit. Input Devices

11. 11 Input Devices Photoelectric switch: Transmissive type Reflective type Encoder: The term encoder is used for a device that provides a digital output as a result of angular or linear displacement. An increment encoder detects changes in angular or linear displacement from some datum position. An absolute encoder gives the actual angular or linear position.

12. 12 Fig: Incremental Encoder Fig: Absolute Encoder Input Devices Encoder:

13. 13 Input Devices Temperature sensors Thermocouple LM3911N circuit for on–off control Bi-Metallic Strip RTD

14. 14 Input Devices Figure: LVDT Displacement Sensor:

15. 15 Input Devices Strain Gauge Pressure Sensors

16. 16 Input Devices Liquid Level Sensors Orifice Flow Meter

17. 17 Smart Sensors The term smart sensor is used for a sensor which is integrated with the required buffering and conditioning circuitry in a single element. The circuitry with the element usually consists of data converters, a processor and firmware, and some form of non-volatile EEPROM memory. Such sensors can be programmed for specific requirements. The IEEE 1451.4 standard requires the non-volatile EEPROM embedded memory to hold and communicate data which will allow a plug-and-play capability. It thus would hold data for the identification and properties for the sensor and might also contain the calibration template, so facilitating digital interrogation.

18. 18 Output devices Relay The digital signal from the output channel of a PLC is used to control an actuator which in turn controls some process. The term Actuator is used for the device which transforms the electrical signal into some more powerful action which then results in the control or action in the process. D.C. Motor

19. 19 Output devices Stepper Motor 2 Types Permanent Magnet SM Variable Reluctance SM

20. 20 Output devices DCV Solenoid Operated Valve

21. 21 Examples of applications Conveyor belt Liquid Level Monitoring Lift Robot Control System Industrial Applications

22. 22 References: Programmable Logic Controllers Fourth Edition W. Bolton

23. 23 Thank You !