1. Introduction — Push Buttons Are the Most Frequently Used Control Components
Push buttons are the most frequently operated components in any control system.
Operators rely on them for:
- Machine start/stop
- Mode switching
- Emergency actions
- Safety signaling
Choosing the right button type and color improves efficiency, safety, and human–machine interaction.
2. Structure of Push Button Switches
2.1 Momentary vs Latching
- Momentary (self-reset):
Returns when released. Used for start, jog, and most operations. - Latching (self-lock):
Physically locks when pressed. Less common today except in special cases.
2.2 NO (Normally Open) vs NC (Normally Closed)
- NO: Sends signal when pressed
(Start, Mode Select, Command Input) - NC: Breaks circuit when pressed
(Stop, Emergency Stop, Safety Input)
2.3 Illuminated Push Buttons (LED)
Include:
- LED indicator
- Replaceable or built-in lamp
- Multicolor design in some models
Useful for showing machine states.
3. Button Color Meaning According to Industrial Standards
| Color | Meaning |
|---|---|
| 🔴 Red | Emergency Stop / Stop |
| 🟢 Green | Start / Run |
| 🟡 Yellow | Warning / Abnormal Condition |
| 🔵 Blue | Function / Mode Select |
| ⚪ White | Generic / Universal |
Color coding helps operators identify functions instantly, reducing error risk.
4. Engineering Layout Guidelines
4.1 Button Height & Position
- Eye-level or hand-level for comfortable access
- Emergency stop placed at highest reach priority
4.2 Button Arrangement Order
Standard order (left → right):
Stop → Start → Mode/Function
This improves usability and reduces mis-operations.
4.3 Combined Use with Indicator Lights
Examples:
- Green button + green indicator = “Machine Running”
- Red button + red indicator = “Stop / Alarm”
5. Wiring Logic of Push Buttons
5.1 Latching (Self-Lock) Circuit
Typical for motor control:
Start (NO) → Coil → Auxiliary NO
Stop (NC) → Interrupt
5.2 Start–Stop Circuit
The simplest and most widely used circuit:
- Start = NO
- Stop = NC
- Auxiliary contact holds the circuit
5.3 Push Button → PLC Input
Buttons send signals to PLC digital inputs (DI):
- NO → rising edge detection
- NC → fail-safe logic
6. Common Problems in Push Buttons
6.1 Contact Oxidation
Symptoms:
- No response
- Intermittent behavior
Fixed by cleaning or replacing contacts.
6.2 Button Pressed but No Action
Possible causes:
- Broken internal spring
- Loose terminals
- Incorrect wiring
6.3 LED Indicator Failure
Caused by:
- LED burnout
- Incorrect voltage
- Internal wiring fault
7. Best Practices
✔ Use Industrial IP65/67 Buttons
Resists dust, oil, and moisture.
✔ Use Quick-Connect Terminals
Improves wiring efficiency and reduces loose connection risk.
✔ Periodically Inspect Button Feel and Spring Response
Ensures long-term reliability.
✔ Emergency Stop Must Use Mechanical Latching
Required for safety compliance.
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