Podcast
Questions and Answers
What type of current is most commonly used for digital inputs in PLCs?
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?
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?
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?
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?
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?
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?
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.
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?
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 __________.
Sensors detect flow rate and relay information to the __________.
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Match the following descriptions with the appropriate terms:
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.
