PLC INPUT&OUTPUT DEVICES.pptx
- 1. INPUT- OUTPUT DEVICES REPORTER: JANNA RICA P. BEASON
- 2. INPUT DEVICES • The term sensor is used for an input device that provides a usable output in response to a specified physical input (Thermocouple).
- 3. Examples of Digital Input Devices in PLCs 1. START/STOP Push Buttons Start/Stop Pushbuttons are usually located in a PLC control panel. They function either by making or breaking contact. They are thus classified as either Normally Closed (NC) or Normally Open (NO). 2. Proximity Sensors Proximity switches are used to detect the presence of an item without making contact. A proximity switch that can be used with metallic and non- metallic objects is the capacitive proximity switch. 3. Limit Switch The term limit switch is used for 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.
- 5. OUTPUT DEVICES • Devices that are driven by the output ports of the PLC,. These devices are switched on/off from the output channel of the PLC which in turns controls some process.
- 6. Examples of Digital Output Devices in PLCs 1. Indicator Lights The simplest example of a digital output device that can be controlled by a PLC is the light bulb. As a digital output from the PLC can turn ON the light bulb or turn it OFF. 2. Alarms Alarms in PLC-controlled systems provide notifications of higher urgency. 3. Actuators These are devices that convert an electrical or control signal into linear or rotary mechanical motion. 4. Solenoid Valves A solenoid valve is simply an electromechanical valve that is electrically controlled.
- 9. PROBLEMS Troubleshooting digital input • If power is present for the input in question, since faults in the wiring and field devices can burn a fuse, trip a switch or cause another power interruption. • If there is no input power, determine and rectify the cause of the failure before continuing. If there is input power, connect a voltmeter through the input. • Activate the input device in the field and measure the voltage at the input of the PLC to determine if it changes properly when the field device changes state.
- 10. PROBLEMS Troubleshooting digital output • If the indicators in the module do not reflect the forced condition, change the output module. • If the indicators are observed to be reacting to the forced state, measure the voltage across the output device to see that it’s changing as the state of the output changes. • If the voltage is changing but the device is not reacting, the problem is in the output device. If the voltage is not changing, the problem can most likely be found in the field wiring.
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