SPC/Digimatic Protocol Scales
SPC (Statistical Process Control) and Digimatic are serial digital protocols commonly used in calipers and some DRO scales. These provide absolute position data in a digital format.
Protocol Characteristics
- Serial data: Digital position transmitted as serial packets
- Absolute position: No need for homing or reference
- Update rate: Typically 2-10 Hz
- Resolution: Usually matches the display resolution
Common Protocols
Mitutoyo Digimatic
- 52-bit data packet
- Includes sign, decimal point, and units
- Standard 4-pin connector
- Clock and data lines
iGaging Protocol
- 21-bit or 24-bit variants
- Simpler packet structure
- Compatible with many Chinese scales
Shahe Protocol
- Similar to iGaging
- 24-bit data format
- Common in budget calipers and scales
Typical Pinouts
Standard 4-pin (Mitutoyo style)
- Pin 1: Ground (0V)
- Pin 2: Clock
- Pin 3: Data
- Pin 4: Power (+1.5V)
6-pin variants (some Chinese scales)
- Additional pins for different voltage levels
- May include enable/request lines
Compatible Devices
- Mitutoyo digital calipers and height gauges
- iGaging DRO scales and calipers
- Shahe digital calipers
- Many Chinese "SPC output" scales
- Some Fowler digital tools
TouchDRO Compatibility
Fully supported:
- TDA-4xx series (all protocols)
- DIY adapters with appropriate firmware
- Dedicated iGaging/Shahe adapter kits
Protocol support by adapter:
- Mitutoyo Digimatic: TDA-4xx only
- iGaging: TDA-4xx and DIY adapters
- Shahe: TDA-4xx and DIY adapters
Advantages
- Absolute position (no homing required)
- Simple wiring (fewer connections)
- Built-in error checking
- Works with existing calipers/tools
Limitations
- Lower update rates than quadrature
- May have resolution limitations
- Battery-powered devices may sleep
- Protocol variations between manufacturers
Setup Considerations
- Verify protocol compatibility before purchase
- Some devices require "wake up" signals
- Check voltage requirements (1.5V vs 3.3V vs 5V)
- Consider update rate for your application
Troubleshooting
- No data: Check power and protocol selection
- Garbled readings: Verify clock/data line connections
- Intermittent operation: Device may be sleeping
- Wrong resolution: Check protocol configuration