PWM vs 0–10V: How Your Controller Actually Talks to the VFD

When your CNC controller tells the spindle to run at a specific RPM, it must communicate that request to the VFD.

That communication happens in one of two ways:

True 0–10V analog voltage
PWM (Pulse Width Modulation)

Understanding the difference removes most spindle speed confusion.

Two Ways to Send Speed Commands

1️⃣ True 0–10V Analog (The Ideal Method)

This is the cleanest and most stable method.

The controller outputs a real voltage between:

0V = 0 RPM
10V = Maximum RPM

The VFD simply reads that voltage and scales it proportionally.

Example:

Voltage	Spindle Speed (24,000 max)
5V	12,000 RPM
7.5V	18,000 RPM
10V	24,000 RPM

This method is:

Smooth
Stable
Predictable
Industrial standard

Controllers like Masso and Centroid typically provide true analog output.

2️⃣ PWM (Voltage Simulation)

Many hobby CNC controllers do not output true analog voltage.

Instead, they output a digital PWM signal.

PWM works by rapidly turning a 5V signal on and off. The average voltage over time simulates analog.

The VFD then interprets that average as speed.

But here’s the key:

PWM is a simulation of voltage.

Not actual voltage.

Why Cheap Controllers Don’t Output Perfect Voltage

A controller labeled as:

“0–5V PWM”
“0–10V PWM”

Rarely outputs exactly 5.00V or 10.00V.

In reality, you might see:

4.82V
4.96V
9.7V
Non-linear scaling across the range

This is normal behavior for hobby-level electronics.

It is not a defect.

But it does affect spindle speed accuracy.

What This Looks Like in Practice

You may notice:

Spindle never quite reaches full RPM
Spindle starts too fast
RPM does not match commanded value
Speed feels compressed or inconsistent

This is almost always scaling mismatch, not wiring failure.

When You Need a Digital-to-Analog Converter

Some controllers output PWM that is too noisy or unstable for direct VFD use.

In those cases, a PWM-to-0–10V converter is required.

The converter:

Accepts digital PWM
Converts it into a clean analog 0–10V signal
Feeds that to the VFD’s analog input

This improves:

Stability
Maximum RPM accuracy
Low-speed control resolution

Where the Converter Physically Goes

The converter should be installed:

Near the CNC controller
Between the controller PWM output and the VFD analog input

Signal flow:

Controller PWM → Converter → VFD Analog Input

The converter:

Receives power (often from VFD 10V reference and ground)
Outputs a clean voltage to the VFD

Keep signal wires short and away from high-voltage spindle cables.

Scaling Adjustments Are Normal

Even with true 0–10V analog, some tuning may be required.

The EM61 VFD allows:

Minimum frequency adjustments
Maximum frequency scaling
Fine mapping between voltage and RPM

This means you can adapt the VFD to your controller’s real-world output.

You are not expected to have a mathematically perfect controller.

The VFD is designed to compensate.

Matching Controller Settings to the VFD

Proper spindle behavior depends on:

Correct RUN source
Correct frequency source
Correct scaling
Matching acceleration timing

If speed feels wrong, the problem is usually:

Signal scaling
Voltage range mismatch
Acceleration timing mismatch

Not hardware failure.

True Analog vs PWM Summary

Feature	True 0–10V	PWM
Stability	Excellent	Varies by controller
Accuracy	High	Depends on quality
Requires converter	No	Sometimes
Industrial standard	Yes	No

When to Upgrade to True Analog

You may benefit from true analog control if:

You need precise RPM repeatability
You are cutting aluminum or steel
You run consistent production jobs
You want minimal tuning

For wood and hobby work, PWM is usually acceptable when tuned correctly.

Key Takeaway

Your controller does not send RPM.

It sends voltage.

The VFD converts voltage into spindle speed.

If the voltage is imperfect, the RPM will be imperfect.

That’s normal.

The system is designed to accommodate it.

Understanding that prevents unnecessary troubleshooting and eliminates most “my spindle speed is wrong” tickets.