A digital input is a type of electrical signal that can only exist in one of two states, typically representing ON or OFF.
In the world of automation and electronics, digital inputs are fundamental for receiving information from devices that have discrete states. Unlike analog inputs which can represent a range of values, a digital input is binary – it's either one state or the other.
Understanding Digital Inputs
Digital inputs are used to check the status of any devices whether it is ON or OFF. This binary nature makes them ideal for monitoring simple conditions.
Think of a light switch – it's either on or off. A digital input is how a control system, like a programmable logic controller (PLC) or a microcontroller, "knows" the state of such a switch or similar device.
Binary States (0 and 1)
The two states of a digital input are commonly referred to as Binary 0 and Binary 1.
- Binary 0: Represents the OFF or Low state.
- Binary 1: Represents the ON or High state.
The specific voltage levels that correspond to these states depend on the electrical standard or the device being used.
Voltage Levels Example
As stated in the reference: For an Input module of 24 Vdc, 0 Vdc acts as the OFF state (Binary 0) and 24 Vdc acts as the ON state (Binary 1).
This is a common standard in industrial automation. Other systems might use different voltage levels, such as 5Vdc (TTL logic), but the principle of two distinct voltage levels representing the binary states remains the same.
Devices Using Digital Inputs
Many real-world devices communicate their status using digital signals:
- Switches: Limit switches, push buttons, toggle switches (open/closed).
- Sensors: Proximity sensors (object detected/not detected), Photoelectric sensors (light beam broken/not broken), Level switches (liquid level high/low).
- Status Indicators: Alarm conditions (active/inactive), equipment status (running/stopped).
Applications of Digital Inputs
Digital inputs are crucial in various systems:
- Industrial Automation: Monitoring machine states, safety interlocks, tracking product on a conveyor belt.
- Building Automation: Detecting door/window status, motion detection, alarm system zones.
- Automotive: Reading sensor states like brake pedal pressed, door ajar.
- Robotics: Checking positions, detecting obstacles.
By reading digital inputs, control systems can make decisions and trigger actions based on the current state of connected devices.
| State | Representation | Example Status (24Vdc System) |
|---|---|---|
| OFF / Low | Binary 0 | 0 Vdc |
| ON / High | Binary 1 | 24 Vdc |
In summary, a digital input provides a simple, reliable way for a control system to understand whether a device is in one of its two possible states, typically ON or OFF, based on distinct voltage levels.
