Denki Control Lab Practical PLC and electrical control guides
Control Basics

Encoder Basics: Wiring, Pulse Signals, and A/B/Z Phases Explained

An encoder converts rotation or movement into electrical signals. This guide explains pulse signals, A/B/Z phases, incremental and absolute types, and basic PLC input checks.

  • Understand what an encoder tells a control system.
  • Learn the meaning of A phase, B phase, and Z phase.
  • Check wiring, signal type, and PLC high-speed input conditions calmly.
Start with the overview Jump to field checks

Good for

  • Beginners learning what an encoder does.
  • People checking pulse signals and PLC high-speed inputs.
  • Field workers who want to understand A/B/Z phase basics.

Not the first topic if

  • You need a manufacturer-specific wiring manual.
  • You are setting servo parameters without the official documentation.
  • You have not confirmed the encoder model, output type, and PLC input module.

Main conclusion

  • An encoder outputs position or movement information as signals.
  • A/B phase helps detect movement direction and amount.
  • Wiring and input specifications must match the PLC or controller.

Quick navigation

Overview Encoder types Pulse signals A/B/Z phases Wiring basics Field checks Summary

What is an encoder?

An encoder is a device that converts rotation, position, or movement into electrical signals.

In factory automation, encoders are used when a controller needs to know how far something moved, how fast it is rotating, or where a shaft or mechanism is positioned.

A simple sensor may only tell ON or OFF. An encoder gives more detailed movement information, often as pulses or digital position data.

Overview of an encoder converting shaft rotation into electrical pulse signals for a PLC or controller
An encoder reads rotation or movement and sends signal information to a PLC, counter, servo amplifier, or controller.
Senior technician character
Senior

An encoder is not just an ON/OFF sensor. It gives the controller information about movement, count, speed, or position.

Junior technician character
Junior

So when I see encoder wiring, I should think about pulse signals, input speed, and whether the controller can read those signals correctly.

Model differences matter

Output method, power supply voltage, resolution, maximum response frequency, connector pinout, and wiring method differ by encoder model. Always confirm the official manual for the actual device.

Incremental and absolute encoders

The two common ideas are incremental counting and absolute position information.

Type Basic idea Field image Common caution
Incremental encoder Outputs pulses as movement occurs. The controller counts pulses to know movement amount and direction. Position may need origin return or reference after power reset.
Absolute encoder Outputs position information as a value. The controller can know the current position more directly. Communication method, battery, and parameter settings may be involved.
Comparison of incremental and absolute encoders showing pulse count and stored position concepts
Incremental encoders count pulses as movement occurs. Absolute encoders provide position information that can be retained depending on the system.

Beginner takeaway

If you see A phase, B phase, or Z phase pulses, you are usually dealing with incremental encoder-style signals. If you see communication data or absolute position values, the checking method may be different.

Pulse signals: how movement becomes count information

With an incremental encoder, rotation is converted into repeated pulse signals.

Each pulse can represent a small amount of movement. The controller counts these pulses to calculate movement amount, speed, or rotation.

The number of pulses per rotation is often called resolution. A higher resolution can provide finer movement information, but the controller input must be able to read the pulse frequency.

Normal inputs may not be enough

Fast encoder pulses often require a high-speed counter input or dedicated module. A normal PLC input may miss pulses if the frequency is too high.

A phase, B phase, and Z phase

A/B phase is commonly used for direction and count. Z phase is often used as an origin or reference pulse.

A phase B phase and Z phase encoder signal explanation
A and B phases are shifted from each other. That phase difference helps determine direction. Z phase is usually a once-per-rotation reference pulse.

A phase

One of the main pulse signals used for counting movement.

B phase

Another pulse signal shifted from A phase, used to determine direction.

Z phase

A reference pulse that is often used for origin or one-rotation reference.

Direction mismatch

If direction is reversed, check A/B phase wiring and controller settings before changing logic.

Terminology may vary

Some manuals use A, B, Z. Others may show phase names, channel names, or differential signal names. Always check the actual wiring diagram and terminal names.

Basic wiring points

Encoder wiring must match power supply, signal type, input circuit, and cable shielding requirements.

Encoder troubleshooting often starts from simple wiring checks. Confirm the power supply voltage, 0V/common, signal output type, shield connection, and whether the input module is suitable for the encoder.

Check item What to confirm Why it matters
Power supply Voltage rating, polarity, 0V/common. Wrong voltage or missing common can stop signal output.
Output type NPN/PNP, voltage output, open collector, line driver, differential output. The PLC input must match the signal type.
Input speed High-speed input or counter module specification. If the pulse frequency is too high, counts may be missed.
Shield and cable Shielded cable, grounding method, routing away from noise sources. Noise can cause false counts or unstable signals.

Use the drawing and manual together

The machine drawing tells you how the site intended to wire it. The encoder and PLC manuals tell you what the device actually requires.

Field checks when an encoder signal looks wrong

Do not start by replacing the encoder. Separate power, wiring, signal, input, and mechanical conditions.

Field checklist for encoder wiring signal and PLC high-speed input troubleshooting
Check power, common, output type, input module, shield, and mechanical coupling before judging the encoder.

1. Check power

Confirm encoder supply voltage and 0V/common at the connector or terminal.

2. Check signal type

Confirm whether the output is NPN, PNP, open collector, line driver, or another type.

3. Check input specification

Confirm the PLC high-speed input or counter module can read the expected pulse frequency.

4. Check A/B/Z wiring

Confirm terminal names, polarity, and direction-related wiring before changing settings.

5. Check noise and shield

Look for poor shielding, long cable runs, and routing near motors, inverters, or power lines.

6. Check mechanical side

Confirm coupling looseness, shaft slip, mounting gap, vibration, or mechanical damage.

Summary

An encoder is used when a control system needs movement, speed, count, or position information. Incremental encoders commonly output pulse signals such as A phase, B phase, and Z phase.

In the field, encoder problems should be checked in order: power supply, wiring, signal type, input module, pulse frequency, shielding, and mechanical mounting. Do not judge the encoder only from one symptom.

Final takeaway

An encoder is a movement information device. To troubleshoot it, check both the electrical signal path and the mechanical side that creates the movement.

Read these next to connect encoder signals with practical object detection and field input diagnostics.

Proximity Sensor Basics

Understand how proximity sensors detect metal objects and how they connect to PLC inputs.

Photoelectric Sensor Basics

Learn how photoelectric sensors detect objects using light and what to check in the field.

Limit Switch Basics

Review mechanical position detection, contact operation, and basic field checking points.