Calibration Constancy Intercomparison System for Microwave Oven Survey Instruments
This guidance outlines procedures for establishing and maintaining a calibration constancy intercomparison system for microwave oven compliance survey instruments. It aims to ensure proper calibration of instruments used in production testing and quality control programs to verify compliance with the Federal Performance Standard for Microwave Ovens (21 CFR 1030.10).
What You Need to Know? 👇
What is a calibration constancy intercomparison system for microwave oven compliance instruments?
A system that demonstrates instrument calibration remains within prescribed limits over time, minimizing the need for frequent absolute recalibration. It consists of a microwave source, radiated power monitor, anechoic environment with radiator, and local calibration reference.
How often must microwave survey instruments undergo daily polarization checks?
Daily checks are required before each use to detect gross shifts in response indicating potential instrument damage. The polarization ellipticity error must remain within manufacturer specifications, typically ±5 percent or 10 percent total error.
What is the 10 percent constancy requirement for compliance instruments?
Each compliance survey instrument’s monthly mean reading must remain within 10 percent of all previous monthly readings since last calibration or repair. Instruments exceeding this limit must be repaired or discarded.
When must the Local Calibration Reference (LCR) undergo absolute calibration?
The LCR requires annual absolute calibration by the instrument manufacturer or qualified facility. It should be set aside from production use to minimize damage and maintain calibration integrity throughout the year.
What is the 2 dB comparison check requirement?
Monthly verification that the least and most sensitive instruments don’t disagree by more than 2 dB (ratio ≤1.59). This cumulative check compares highest to lowest polarization readings from all instruments since last LCR calibration.
How frequently should compliance survey instruments receive periodic recalibration?
All compliance determination instruments (except LCR and RPM) should return to manufacturer or qualified facility for absolute calibration at least once every 3 years, following good engineering and manufacturing practices.
What You Need to Do 👇
Recommended Actions
- Establish calibration constancy intercomparison system with required components
- Implement daily check program:
- Check polarization response before use
- Document results for each instrument
- Remove failed instruments from service
- Implement monthly check program:
- Verify reference field constancy
- Check compliance instruments against 10% criteria
- Perform 2 dB comparison checks
- Maintain required documentation
- Set up annual calibration schedule:
- LCR absolute calibration
- Other instruments as recommended by manufacturers
- Create documentation system:
- Daily check records
- 30-day instrument comparison logs
- 12-month historical records
- Calibration and repair records
- Establish procedures for:
- Handling failed instruments
- Repair and recalibration processes
- Record renewal requirements
- Train personnel on:
- System operation
- Check procedures
- Documentation requirements
- Failure response protocols
Key Considerations
Non-clinical testing
- Daily checks of polarization response required before instrument use
- Monthly checks of reference field and compliance instruments required
- Annual absolute calibration of Local Calibration Reference (LCR) required
- Periodic recalibration (every 3 years) of all compliance instruments recommended
Safety
- Polarization ellipticity error must meet manufacturer specifications
- Reference field readings must agree within 10% between checks
- Survey instruments must maintain readings within 10% between checks
- Maximum 2 dB difference allowed between most and least sensitive instruments
Other considerations
- System requires microwave source, radiated power monitor, anechoic environment, and local calibration reference
- Detailed documentation required for all checks and calibrations
- Specific procedures for repair and recalibration after failures
- Temperature monitoring during checks recommended
Related references and norms 📂
- 21 CFR 1030.10: Federal Performance Standard for Microwave Ovens