| PID Feedback Loss | Refer to the value of PID feedback value less than value of P4.0.18 and duration of P4.0.19 |
|
ERR20 – PID Feedback Loss
What this means
ERR20 indicates that the VFD has detected a loss or abnormality in the PID feedback signal.
In simple terms, the VFD is expecting a feedback signal as part of a PID (Proportional–Integral–Derivative) control loop, and that signal is either missing, too low, or not behaving as expected for a configured period of time.
Why This Happens
PID control is typically used in applications where the VFD must regulate speed, pressure, flow, or torque based on external feedback, such as:
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Encoders
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Sensors
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Analog feedback signals
If the VFD is configured to expect PID feedback but does not receive it, ERR20 is triggered.
Important Note for CNC Users
Most CNC spindle applications do NOT use PID feedback control.
CNC spindles are typically controlled using:
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PWM or analog speed commands
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Open-loop RPM control
If PID mode is enabled unnecessarily, ERR20 can occur even though nothing is actually wrong.
Most Common Causes We See
1. PID mode enabled when no feedback device is present (most common)
This is by far the most frequent cause.
If the VFD is set to use PID control but:
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No feedback sensor is installed
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No signal is wired to the feedback input
ERR20 will occur.
2. Incorrect PID feedback wiring
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Feedback signal not connected
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Incorrect terminal used
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Broken or loose wire
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Incorrect signal polarity or scaling
3. PID thresholds set too aggressively
Parameters controlling:
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Minimum feedback value (P4.0.18)
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Feedback loss duration (P4.0.19)
May be set too tightly for real-world conditions.
4. Faulty or unstable feedback signal (less common)
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Defective sensor
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Noisy signal
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Power or grounding issues affecting the sensor
This applies only if PID feedback is intentionally used.
What to Check First
Step 1: Determine if PID control is actually needed
Ask yourself:
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Are you using an external feedback sensor?
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Is closed-loop PID control required for your application?
For most CNC spindle setups, the answer is no.
Step 2: Disable PID control if not required
If PID is not needed:
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Disable PID mode in the VFD
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Return the drive to standard open-loop speed control
This usually resolves ERR20 immediately.
Step 3: If PID is required, verify feedback wiring
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Confirm the feedback device is installed
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Verify correct terminals are used
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Check wiring continuity and signal stability
Step 4: Review PID parameters
Check:
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P4.0.18 – Minimum acceptable feedback value
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P4.0.19 – Allowed duration before fault
Ensure these values match real operating conditions.
What ERR20 Is Not
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Not a spindle motor fault
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Not a cutting load issue
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Not a power or voltage problem
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Not EMI related
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Not a controller software issue
ERR20 is strictly related to PID control logic and feedback signals.
Recommended Action for CNC Spindle Systems
For nearly all CNC spindle applications:
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PID control should be disabled
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Open-loop RPM control should be used instead
PID feedback is typically unnecessary and can introduce nuisance faults.
When to Contact Support
If:
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You intentionally use PID control
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Feedback wiring is confirmed correct
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ERR20 persists unexpectedly
Support can help verify proper PID configuration for your specific use case.
Summary
ERR20 means the VFD has detected a loss or abnormality in PID feedback.
Most common cause:
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PID mode enabled without a valid feedback signal
For CNC spindle use, PID control is usually unnecessary and should be disabled.
