How to Calibrate a Bourdon Tube Gauge

How to Calibrate a Bourdon Tube Pressure Gauge

Bourdon tube pressure gauges are widely used in industrial settings due to their reliability, accuracy, and mechanical simplicity. To maintain precision, regular pressure gauge calibration is essential. This guide explains how a Bourdon tube gauge works, outlines calibration methods, and dives into common errors and their corrections.

Whether you’re in manufacturing, energy, or process control, knowing how to calibrate these gauges ensures operational safety and compliance.

Understanding the Bourdon Tube Mechanism

A Bourdon tube is a curved, flexible tube fixed at one end and sealed at the other. When internal pressure increases, the tube tends to straighten. This motion is transferred via an S-link to a gear mechanism (called a movement), which rotates the pointer on the dial.

Key internal components include:

  • The C-shaped or helical Bourdon tube

  • A quadrant gear

  • A pinion attached to the pointer spindle

  • A slotted link for movement translation

This mechanical setup converts the tube’s deflection into rotary pointer motion, creating a readable pressure value on the dial. However, the mechanism’s inherent non-linearity requires precise calibration to ensure accuracy.

Why Calibration Matters

Over time, pressure gauges drift due to mechanical wear, process stresses, and environmental factors. A miscalibrated gauge can result in:

  • Inaccurate readings

  • Safety hazards

  • Product defects

  • Non-compliance with standards

Calibration involves comparing the gauge reading to a known, accurate pressure reference (like a deadweight tester), and making adjustments based on the observed discrepancies.

As-Found vs As-Left Calibration

  • As-Found: The gauge’s accuracy before any adjustments. This helps assess past performance and potential impact on operations.

  • As-Left: The condition after adjustments are made to bring the gauge within acceptable limits.

Maintaining both records is vital for compliance and traceability in industrial environments.

Types of Calibration Errors

Understanding the types of calibration errors is key to making effective corrections.

1. Zero Error

  • The pointer is off by a fixed value across the scale.

  • Correction: Remove and reposition the pointer or adjust using the micro-adjustment screw.

2. Span Error

  • The pointer moves too much or too little compared to the applied pressure.

  • Correction: Adjust the linkage pivot in the slot—move it closer to increase travel or farther to decrease it.

3. Linearity Error

  • The pointer doesn’t follow a straight calibration curve.

  • Correction: Set the link-slot angle to 90º at 50% of full scale to optimize mid-range accuracy.

4. Combination Errors

  • A mix of zero and span errors (common in most cases).

  • Correction: First correct the span, then reset the pointer for zero alignment.

How to Calibrate a Bourdon Tube Pressure Gauge

Step-by-Step Guide:

Apply Known Pressure: Use a certified reference source.

Compare Readings: Note deviations at 0%, 50%, and 100% of the scale.

Identify Error Type: Analyze the pattern to determine zero, span, or linearity errors.

Adjust Mechanism:

    • For zero: Adjust the pointer.

    • For span: Adjust linkage pivot.

    • For linearity: Optimize linkage angle.

    • Repeat and Verify: Recheck after each adjustment for improved accuracy.

Tip: Limit final adjustment errors to no more than 80% of the allowable tolerance to account for other potential deviations.

Other Factors Affecting Accuracy

  • Parallax Error: Occurs when viewing the pointer from an angle. Use knife-edge pointers and mirrored dials to reduce this.

  • Resolution Error: Arises when estimating values between scale markings. Mitigate with high-resolution dials.

Final Thoughts

Calibrating a Bourdon tube pressure gauge is both a technical skill and a safety necessity. By understanding the mechanical design, identifying error types, and adjusting precisely, you can ensure reliable performance and prolong the gauge’s lifespan.

At Blanes Pressure Solutions, we provide expert calibration services, high-precision tools, and technical support to keep your operations running smoothly.

Need Help with Pressure Calibration?
Visit our Calibration & Testing Services or Contact Us to schedule a professional assessment.

We also offer SANAS traceable calibrations complete with a certificate, valid for 1 year on our premises.

Blanes Pressure Solutions supplies a comprehensive range of pressure measurement instruments.

Blanes Pressure Solutions was founded in 2002 to take over the pressure business of Blanes Instruments CC, and can trace its pedigree back to 1893, when Robert Blane left Scotland to make his fortune on the Witwatersrand.

For more information on placing orders, after care and maintenance services you can contact our Sales Manager Ronel Olivier on ronel@pressuresolutions.co.za or 011 422 1749.