Questions and Answers
What type of current is most commonly used for digital inputs in PLCs?
What is the purpose of a sensing element in a digital input circuit?
When a sensing element trips, what happens to the digital input signal?
Which of the following could be considered a digital input for a PLC?
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What is the difference between a 24 Volt DC and a 240 Volt AC input configuration?
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What is the main function of a PLC's input card?
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What does the Purdue model aim to address in OT networks?
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Input output modules are analog devices that sense the status of real-world conditions.
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What are the two communication pathways that vendors are moving towards for inputs and outputs?
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Sensors detect flow rate and relay information to the __________.
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Match the following descriptions with the appropriate terms:
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Study Notes
Digital Inputs Overview
- Digital inputs represent the simplest binary state with only two conditions: "ON or OFF," "OPEN or CLOSED," or "0 or 1."
- The state of a digital input can be continuously plotted over time, showing only values of 1 or 0.
Example Applications
- In pump systems, a digital input indicates whether a pump is running ("ON") or not ("OFF").
- For tank monitoring, discrete inputs could signal "high level" and "low level" alarms, corresponding to water levels reaching specific limits.
Alarm Functionality
- When the water level in a tank reaches the high limit, the "high level" alarm activates (value becomes "1"), otherwise, it remains "0."
- Similarly, the same logic applies for the low-level alarm when the water reaches its lower limit.
Wiring Configurations
- Digital inputs are typically connected to a Programmable Logic Controller (PLC) using various voltage levels of AC or DC.
- Common input configurations include:
- 24 Volt DC with a switching range of 100 to 500 mA
- 110 Volt AC with a switching current of 1A to 2A
- 240 Volt AC with a switching current of 1A to 2A using triac solid state switching
Operation of Sensing Elements
- The sensing elements, such as level switches and proximity switches, function as the interface with the PLC.
- Once a sensing element trips (when the switch closes), the circuit completes, allowing an external voltage signal to reach the controller.
- The PLC registers this action by writing a "1" in its memory.
- Conversely, when the switch opens and no voltage is detected, the PLC updates its memory by recording a "0".
Importance of Instrumentation and Output Controllers
- Instrumentation and output controllers are essential for managing inputs and outputs in operational technology (OT) networks.
- Inputs and outputs are mapped into memory addresses within controllers for effective control and monitoring.
Purdue Model and ISA S99 IEC 62443 Standard
- The Purdue model serves as a framework to analyze the architecture of OT networks, based on the ISA S99 IEC 62443 standard.
- It categorizes various components of an OT network into functional levels, enhancing understanding and management.
Physical Process Level
- At the ground level, sensors monitor conditions such as flow rate.
- Detected data is processed in real-time by analog or digital input cards and stored as digital signals within processors.
Input/Output Modules
- Input/output modules are digital devices that sense real-world conditions and directly influence physical processes in a facility.
- Automation relies on these modules to perceive environmental changes and control processes efficiently.
Traditional vs. Modern Communication Methods
- Traditionally, sensor networks utilized hardwired electrical signals (e.g., 4 to 20 milliamps) for connectivity to controllers.
- A notable shift towards bus communications and wireless technologies is occurring, allowing for flexible placements of sensors in extensive environments such as warehouses and outdoor facilities.
Module Structure
- The module will begin with a focus on wired input/output connections before exploring modern communication pathways.
- Hands-on exercises will provide practical experience with instrumentation and output controllers.
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Description
Understanding digital inputs in industrial automation, including their binary states, continuous plotting, and example applications in pump systems and tank monitoring.
