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10. Sensor Calibration



Table of Contents



10.1 Overview

ACRouter supports sensor calibration to ensure accurate voltage and current measurements. Calibration is performed by calculating a multiplier coefficient based on measurements using reference instruments.


Why Calibration is Needed?

  • Manufacturing tolerances: Each sensor has small deviations from nominal values
  • Grid voltage differences: Different countries use different standards (230V, 110V, 220V, 240V, etc.)
  • Measurement accuracy: Calibration ensures ±2% accuracy or better


Factory Default Values

On first boot or after reset, the following values are used:

Sensor Model Multiplier Note
Voltage ZMPT107 328.57 Calibrated for 230V (0.70V RMS = 230V AC)
Current SCT-013-030 30.0 Maximum 30A



10.2 ZMPT107 Voltage Sensor Calibration


⭐ Automatic Calibration (Recommended)

Starting with version 2.0, ACRouter supports automatic voltage sensor calibration. The system automatically measures the sensor output (VDC RMS) and calculates the calibration multiplier.

Automatic Calibration Procedure

Step 1: Measure Grid Voltage

Use a multimeter to measure the actual grid voltage:

python
Example:
Multimeter shows: 232.5V AC

Step 2: Run Auto-Calibration

Enter the command with the measured voltage:

bash
hardware-voltage-calibrate 232.5

Step 3: System Automatically:

  1. Measures current sensor output (VDC RMS) - e.g., 0.72V
  2. Calculates multiplier: 232.5 / 0.72 = 322.92
  3. Saves calibration data to NVS

Example Output:

python
Auto-calibrating voltage sensor...
Measured grid voltage (from multimeter): 232.5 V
Raw sensor VDC output: 0.72 V
Calculated multiplier: 322.92
Sensor type: ZMPT107

Configuration updated:
  nominal_vdc = 0.72 V (measured)
  multiplier = 322.92

Calibration saved to NVS. Please reboot to apply: reboot

Step 4: Reboot

bash
reboot

Benefits of Automatic Calibration:

✅ No need to adjust sensor potentiometer manually
✅ Works with any sensor output voltage (0.5V, 0.7V, 1.0V, etc.)
✅ Automatically updates nominal_vdc to actual measured value
✅ More accurate and faster calibration

Via Web API:

bash
curl -X POST http://192.168.4.1/api/hardware/voltage/calibrate \
  -H "Content-Type: application/json" \
  -d '{"measured_vac": 232.5}'

Via Web Interface:

  1. Open http:///settings/hardware
  2. Find "Voltage Sensor Auto-Calibration" section
  3. Enter measured grid voltage (VAC)
  4. Click "Calibrate" button
  5. Reboot device


Manual Calibration (Legacy Method)

For compatibility with older versions or special cases, manual calculation can be used.

Calibration Principle

The ZMPT107 sensor is factory-calibrated so that:
- Nominal grid voltage ≈ 0.70V RMS output (may vary ±0.1V)
- Formula: multiplier = V_measured / V_sensor_vdc

Manual Calibration Procedure

Step 1: Preparation

  1. Connect ACRouter to mains power
  2. Connect to serial port (115200 baud)
  3. Ensure ZMPT107 sensor is connected to configured GPIO

Step 2: Measure Grid Voltage

Use a multimeter to measure actual grid voltage:

python
Example:
Multimeter shows: 232.5V AC

Step 3: Check Sensor Output

Execute command to view raw VDC:

bash
hardware-voltage-show

Example output:

python
Voltage Sensor Configuration:
  GPIO: 35
  Type: ZMPT107
  Nominal VDC: 0.70 V (factory default)
  Multiplier: 328.57
  Current reading: 232.5 V (from 0.72 V raw)
                           ^^^^^^ ← use this value

Step 4: Calculate Multiplier

Use the formula with actual sensor VDC:

python
multiplier = V_measured / V_sensor_vdc

For the example above (232.5V / 0.72V):

python
multiplier = 232.5 / 0.72 = 322.92

Step 5: Apply Calibration

Via Console:

bash
hardware-voltage-config-multiplier 322.92

Via Web API:

bash
curl -X POST http://192.168.4.1/api/hardware/config \
  -H "Content-Type: application/json" \
  -d '{
    "adc_channels": [
      {
        "gpio": 35,
        "type": 1,
        "multiplier": 322.92,
        "offset": 0.0,
        "enabled": true
      }
    ]
  }'

Step 6: Reboot

bash
reboot


Important Notes

⚠️ WARNING: The ZMPT107 sensor uses a voltage divider circuit:
- DC bias center: 1.65V DC
- Maximum peak voltage: 3.06V (for 230V AC)
- This is very close to ESP32 ADC maximum input (3.3V)!

Recommendations:
- Do not use with grid voltage above 250V AC
- For voltages above 240V, consider factory recalibration of ZMPT107 (reduce output to 0.60V = 240V)



10.3 SCT-013 Current Sensor Calibration


Calibration Principle

SCT-013 sensors are available in different variants:
- SCT-013-030: 0-30A, output 0-1V
- SCT-013-050: 0-50A, output 0-1V
- SCT-013-100: 0-100A, output 0-1V

Formula: multiplier = I_measured / V_adc


Calibration Procedure

Step 1: Preparation

  1. Connect a known load (e.g., 2000W electric heater)
  2. Measure current using clamp meter
  3. Ensure SCT-013 sensor is properly installed on wire

Step 2: Measure Current

python
Example:
Load: 2000W heater
Grid voltage: 230V
Expected current: 2000W / 230V = 8.7A
Clamp meter shows: 8.65A

Step 3: Check Current ADC Reading

Execute command:

bash
status

Find currents:

python
Power Measurements:
  Voltage:     230.0 V
  Current (Load):   7.2 A    ← Uncalibrated current
  Current (Grid):   0.0 A
  ...

Step 4: Calculate Multiplier

Use the formula:

python
multiplier_new = multiplier_old × (I_measured / I_current)

For the example above:

python
multiplier_old = 30.0  (factory default SCT-013-030)
I_measured = 8.65A (clamp meter reading)
I_current = 7.2A (ACRouter reading)

multiplier_new = 30.0 × (8.65 / 7.2) = 36.04

Step 5: Apply Calibration

Via Web API:

json
{
  "adc_channels": [
    {
      "gpio": 39,
      "type": 2,
      "multiplier": 36.04,
      "offset": 0.0,
      "enabled": true
    }
  ]
}

Step 6: Verification

Reboot and verify:

bash
reboot
bash
status

Now current should show accurately:

python
Power Measurements:
  Current (Load):   8.65 A    ← Accurate value!


Important Notes

  • For accurate calibration use stable resistive load (heater, incandescent lamps)
  • Do NOT use for calibration: switching power supplies or motors (high inrush current)
  • Minimum current for calibration: 5A (below this threshold ADC noise affects readings)



10.4 Saving Calibration

All configuration changes are automatically saved to NVS (Non-Volatile Storage) and persist after reboot.


Verify Saving

After reboot, execute:

bash
hardware-config

You should see updated multiplier values.



10.5 Reset to Factory Defaults


Via Console

bash
hardware-reset

Then reboot:

bash
reboot


Via Web API

Send POST request to http:///api/hardware/config/reset:

bash
curl -X POST http://192.168.4.1/api/hardware/config/reset



Reference Table: Typical Multiplier Values


Voltage Sensors

Model Grid Calibration Multiplier
ZMPT107 230V AC 0.70V = 230V 328.57
ZMPT107 220V AC 0.70V = 220V 314.29
ZMPT107 240V AC 0.70V = 240V 342.86
ZMPT107 110V AC 0.70V = 110V 157.14


Current Sensors

Model Range Output Multiplier
SCT-013-030 0-30A 1V at 30A 30.0
SCT-013-050 0-50A 1V at 50A 50.0
SCT-013-100 0-100A 1V at 100A 100.0



Useful Commands

bash
# Show current measurements
status

# Show sensor configuration
hardware-config

# Reset to factory defaults
hardware-reset

# Reboot
reboot

Next Section: 11. Troubleshooting

Previous Section: 09. Web API POST

Table of Contents 10.1 Overview 10.2 ZMPT107 Voltage Sensor Calibration 10.3 SCT-013 Current Sensor Calibration 10.4 Saving Calibration 10.5 Reset to Factory Defaults Reference Table: Typical Multiplier Values Useful Commands