NIDEC 22H Series Brushless DC Motors, Features:

  • Clockwise rotation (counterclockwise optional)
  • Signal function available
  • Locked-rotor protection
  • Low inertia
  • Low-noise operation
  • Compact housing: ∅35.8 * 40mm
  • Output power: <15W
  • Brake function
  • Motor with built-in drive circuit
  • (Please refer to the downloadable documents for detailed electrical characteristics and outline dimensions.)

The standard models for the NIDEC 22H Series brushless DC motors are:

  • 12V Standard Model:​ 22H220E031
  • 24V Standard Models:​ 22H893F010 (∅4mm shaft diameter), 22H704J050 (∅3.17mm shaft diameter)


In the control system of a brushless DC motor, a seemingly simple FG signal is often the key to achieving precise control. This article will use the Nidec 22H series motor as an example to analyze the core role of the FG signal and explore how to use it to unlock advanced motor applications.

FG Signal: From Speed Pulse to Control Core

The FG (Frequency Generator) signal is essentially real-time feedback of the motor's speed. Taking the 22H series motor as an example, its FG port outputs 6 pulses for every complete shaft revolution. By measuring the frequency of these pulses, we can accurately determine the motor's real-time speed.

The value of this signal goes far beyond just "reading speed." More importantly, it can form the cornerstone of speed closed-loop control. By feeding the FG signal back to a controller (such as a PLC or microcontroller), the system can continuously compare the "actual speed" with the "set speed" and dynamically adjust the PWM duty cycle or drive current. This enables stable and precise operation across a wide range, from tens of RPM up to the maximum speed, effectively countering the effects of load and voltage fluctuations.

Solving a Common Pain Point: Improving Low-Speed Torque

Many users find that when reducing motor speed via PWM, the motor seems "weak" at low speeds, with a significant drop in output torque. This is because simple PWM speed regulation works by reducing the average input voltage, which inevitably diminishes the motor's driving capability.

Here, introducing closed-loop control using the FG signal is key to solving the problem.​ The system monitors the true speed in real-time via the FG signal. If it detects a speed drop due to increased load, it automatically compensates the control signal (e.g., by increasing the effective voltage), thereby maintaining sufficient torque output even in the low-speed range.

Expanding Possibilities: Five Smart Applications of the FG Signal

Beyond the core function of closed-loop speed stabilization, clever utilization of the pulse characteristics of the FG signal can lead to a series of applications that enhance system performance and intelligence:

  1. Precise Synchronization and Following Master-Slave Synchronization:​ Using the master motor's FG signal as the speed reference for the slave motor enables precise synchronous operation of multiple motors. Ratio Synchronization:​ By proportionally dividing or multiplying the master FG signal, fixed speed ratio (e.g., 2:1) synchronized operation can be easily achieved.
  2. Real-Time Monitoring and Counting Speed Visualization and Alarm:​ Connecting the FG signal to a display or host computer enables digital speed display, data logging, and overspeed/underspeed alarms. Simple Length/Revolution Counting:​ Counting FG pulses allows for estimating cumulative revolutions, useful for simple positioning or quantitative control in applications like winding and feeding.
  3. System Diagnostics and Safety Protection Locked-Rotor and Stall Detection:​ If the FG signal disappears or its frequency is extremely low for an extended period while the drive signal is active, a locked-rotor or stall condition can be immediately determined, triggering shutdown protection to prevent equipment damage. Sudden Load Change Detection:​ Monitoring for sudden, non-commanded drops in FG signal frequency can indirectly indicate a sudden increase in load, triggering corresponding handling procedures.
  4. Economical Motion Control Integration In applications where extreme precision is not required, the FG signal can serve as a low-cost alternative to an incremental encoder, providing speed feedback to a motion controller to build a cost-effective, simple motion control system.

In summary,​ the FG signal acts like the "pulse" of the motor, translating physical rotation into the language of the digital world. Its core value lies in achieving precise and stable operation through closed-loop control. Building on this, it extends to a series of intelligent functions such as synchronization, monitoring, and diagnostics. Fully understanding and utilizing the FG signal is an efficient way to optimize motor control systems and enhance equipment performance and reliability.