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Calibration Table

Overview

The Cal Table (Calibration Table) view displays calibration data for analog channels that require conversion between raw hardware values and engineering units. This is essential for accurate measurements from ADCs, sensors, and other analog devices.

What is Calibration?

Calibration is the process of establishing the relationship between raw hardware readings and actual physical values.

Example:

  • Raw ADC Value: 2048 (12-bit ADC, midpoint)

  • After Calibration: 2.500V (actual voltage)

Without calibration:

  • Values may be inaccurate

  • Offsets and gain errors present

  • Non-linearity not compensated

With calibration:

  • Accurate measurements

  • Offsets corrected

  • Gain adjusted

  • Non-linearity compensated (if calibration table used)

Accessing Calibration Tables

  1. Click Cal Table in the navigation panel

  2. Or Ribbon → Tools → Cal Table

  3. Or Right-click calibrated channel → "View Calibration"

Calibration Table Display

Table Structure

Calibration tables typically show:

Raw Value

Calibrated Value

Unit

Notes

0

0.000

V

Minimum

1024

1.250

V

1/4 scale

2048

2.500

V

Mid-scale

3072

3.750

V

3/4 scale

4095

5.000

V

Maximum

For Temperature Sensors:

Raw Value

Temperature

Unit

0

-40.0

°C

512

0.0

°C

1024

40.0

°C

1536

80.0

°C

2048

120.0

°C

Viewing Calibration Data

Select Channel

  1. Navigate to Cal Table view

  2. Select channel from dropdown or list

  3. Calibration data displayed

Calibration Details

Information Shown:

  • Channel Name: Which channel is calibrated

  • Calibration Type: Linear, Table, Polynomial

  • Number of Points: If table-based

  • Coefficients: If polynomial

  • Gain/Offset: If linear

  • Valid Range: Min/max raw values

  • Units: Engineering units (V, A, °C, etc.)

Graphical View

Some implementations show:

  • Graph of Raw vs. Calibrated

  • Visual representation of curve

  • Non-linearity visible

  • Interpolation points

Calibration Workflows

Verify Calibration

Check if channel calibrated correctly:

1. Navigate to Cal Table
2. Select channel (e.g., ADC_VOLTAGE_1)
3. Review calibration points
4. Verify expected range (e.g., 0-5V)
5. Check number of points (more = better for non-linear)

Apply Known Input

Verify calibration accuracy:

1. Apply known reference (e.g., 2.500V from calibrator)
2. Read channel value in Accordion Pilot
3. Compare to reference value
4. Difference should be within specification
5. If large error, recalibration may be needed

Multi-Point Verification

For critical measurements:

1. Apply multiple known references:
   - 0V (or minimum)
   - 25% scale
   - 50% scale
   - 75% scale
   - Maximum scale
   
2. Read each value

3. Calculate errors:
   Error = (Measured - Actual) / Actual × 100%
   
4. Document results

5. Verify errors within tolerance

Calibration Data Management

Export Calibration Table

Save calibration data:

  1. Right-click calibration table

  2. Select "Export"

  3. Choose format (CSV, Excel, Text)

  4. Save to file

Exported CSV Example:

Channel,Raw,Calibrated,Unit
ADC_1,0,0.000,V
ADC_1,1024,1.250,V
ADC_1,2048,2.500,V
ADC_1,3072,3.750,V
ADC_1,4095,5.000,V

Import Calibration Table

Load new calibration data:

⚠️ Warning: Requires proper authorization and understanding.

  1. Prepare calibration file (correct format)

  2. Use calibration tools or commands

  3. Load via module or system configuration

  4. Verify calibration applied

Note: Calibration modification typically requires:

  • Access to calibration tools

  • Knowledge of calibration procedures

  • Verification equipment

  • Proper authorization

Backup Calibration Data

Save before changes:

1. Export all calibration tables
2. Save to secure location
3. Document date and purpose
4. Include in version control
5. Can restore if needed

Calibration Procedures

Performing Calibration

⚠️ Requires Calibration Equipment:

  • Precision voltage source

  • Precision current source

  • Calibrated multimeter

  • Temperature chamber (for temp sensors)

  • Reference standards

General Procedure:

  1. Prepare Equipment:

    • Calibrate reference equipment

    • Connect to Accordion channels

    • Document setup

  2. Collect Data Points:

    • Apply known reference value

    • Read raw ADC value

    • Record both values

    • Repeat for multiple points (5-20 points)

  3. Generate Calibration:

    • Use calibration software

    • Fit curve or table to data

    • Verify fit quality (R², residuals)

    • Generate calibration file

  4. Load Calibration:

    • Load into Accordion system

    • Verify applied correctly

    • Test with known references

  5. Verify:

    • Apply test values

    • Verify accuracy

    • Document results

    • Archive calibration data

Calibration Interval

Regular recalibration recommended:

  • Critical Measurements: Every 6-12 months

  • General Use: Annually

  • After Repair: Always recalibrate

  • After Exposure: If exposed to out-of-range conditions

Understanding Calibration Errors

Types of Errors

Offset Error:

  • All readings shifted by constant

  • Causes: Reference drift, temperature

  • Correction: Adjust offset term

Gain Error:

  • Error proportional to value

  • Causes: Amplifier gain drift

  • Correction: Adjust gain/slope

Non-Linearity:

  • Error varies across range

  • Causes: Component non-idealities

  • Correction: Multi-point calibration or polynomial

Hysteresis:

  • Different reading depending on direction

  • Causes: Mechanical sensors, magnetic effects

  • Correction: Average up/down readings

Error Specifications

Common Specifications:

  • Full-Scale Error: ±0.1% FSR (Full-Scale Range)

  • Resolution: 12-bit (0.024%), 16-bit (0.0015%)

  • Temperature Coefficient: ±50 ppm/°C

  • Long-Term Stability: ±0.05% per year

Troubleshooting Calibration

Inaccurate Readings

Problem: Channel readings don't match expected

Solutions:

  1. Verify calibration loaded

  2. Check calibration table for channel

  3. Verify reference input accurate

  4. Check for hardware damage

  5. Recalibrate if needed

Missing Calibration

Problem: Channel has no calibration data

Solutions:

  1. Check if calibration required for channel

  2. Load appropriate calibration file

  3. Generate calibration if needed

  4. Contact support for factory calibration

Cal Table Empty

Problem: No calibration points shown

Solutions:

  1. Verify channel has calibration

  2. Check correct channel selected

  3. Reload calibration module

  4. Verify calibration file loaded

Best Practices

  1. Regular Calibration: Follow recommended intervals

  2. Document Everything: Record dates, procedures, results

  3. Use Quality References: Traceable calibration equipment

  4. Verify After Loading: Always test after loading calibration

  5. Backup Data: Archive calibration files

  6. Environmental Control: Calibrate at operating temperature

  7. Multiple Points: More points = better accuracy

  8. Version Control: Track calibration file versions

Calibration Resources

Tools and Equipment

Required for Calibration:

  • Precision voltage/current sources (Fluke, Keysight)

  • Calibrated DMMs (Keithley, HP/Agilent)

  • Temperature chambers/baths

  • Calibration software

  • Reference standards (NIST-traceable)

Software

Calibration Software:

  • Accordion calibration utilities

  • Custom calibration scripts

  • Data analysis tools (Excel, MATLAB, Python)