Accurate CO₂ measurement is critical for applications ranging from HVAC systems to industrial safety monitoring. This guide explains how to calibrate Atomsenses CO₂ sensors using downlink commands, with a focus on the CMD C3: CO₂ Offset protocol.
Why Calibrate CO₂ Sensors?
Field calibration ensures long-term accuracy by compensating for environmental drift. Atomsenses sensors support remote calibration via downlink commands, eliminating the need for physical access in hard-to-reach installations.
Prerequisites
- Atomsenses CO₂ Sensor (Model AS-201 or later)
- Access to device serial port or LoRaWAN® downlink interface
- Atomsenses Configuration Guide (v1.04+)
Step-by-Step: CMD C3 CO₂ Offset Calibration
1. Understanding the Command Structure
The calibration command follows this format:
| Header 1 | Header 2 | CMD | Value | Checksum L | Checksum H |
|---|---|---|---|---|---|
| 0xFF | 0x00 | 0xC3 | XX | CRC Low | CRC High |
Value Calculation: Value = CO₂ Offset (ppm) / 10 in signed char (-128 to +127)
2. Calculating the Offset Value
Example: Apply -350 ppm offset
- Divide by 10: -350 / 10 = -35
- Convert to signed char: Decimal: -35 → Hex: 0xDD
3. Generating the Full Command
Using our example value 0xDD:
| Header 1 | Header 2 | CMD | Value | Checksum |
|---|---|---|---|---|
| 0xFF | 0x00 | 0xC3 | 0xDD | 0xA0 0x99 |
Command Line: FF00C3DDA099
4. Sending the Command
Via LoRaWAN® Downlink:
Use your network server's payload converter: { "fPort": 15, "data": "FF00C3DDA099" }
Verification & Best Practices
- Confirm Calibration:
- Send CMD 0xB1: Read Calibration Status
- Expected response: Offset: -350 ppm
- Pre-Calibration Checklist:
- Allow 30-min warmup in stable environment
- Use reference gas for absolute calibration
- Error Handling:
- ERR 0x81: Invalid checksum → Recalculate CRC
- ERR 0x83: Out-of-range value → Verify signed char conversion
Advanced Configuration Options
For multi-point calibration and temperature compensation, download our comprehensive Configuration Guide which includes:
- Chapter 5: Advanced Downlink Protocols
- Appendix C: CRC Calculation Algorithms
- Troubleshooting Flowcharts
FAQ
Q: How often should I calibrate? A: Every 12 months for general use, 6 months in high-dust environments.
