Pressure Gauge Calibration SOP

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• Document control header (SOP INST 005)
• Purpose, scope and references
• Safety, tools and prerequisites
• Numbered step by step procedure
• Acceptance criteria and records
• Approval block for sign off

1. Purpose

To confirm that pressure gauges indicate within their accuracy class.

2. Scope

Dial pressure and vacuum gauges (EN 837-1 classes 0.6 to 2.5) calibrated in the workshop.

3. References

• EN 837-1 (Bourdon tube pressure gauges)
• Comparator or dead weight tester manual

4. Responsibilities

• Instrument technician: carries out the work and records results.
• Instrument engineer or supervisor: reviews and approves the records.
• Operations: grants the permit, isolates the process and returns the equipment to service.

5. Safety Precautions

• Work only under a valid permit to work and follow the site isolation (lockout tagout) procedure.
• Wear the PPE required for the area: safety helmet, glasses, gloves and safety shoes as a minimum.
• In hazardous areas use certified or intrinsically safe test equipment, or obtain a gas free certificate and hot work permit.
• Inform the control room before starting, and before returning the instrument to service.
• Use the correct test medium: oil free (water or air) for oxygen service gauges, never oil.
• Do not exceed the full scale of the gauge by more than its stated overpressure rating.

6. Tools and Equipment

• Hydraulic or pneumatic comparator, or dead weight tester
• Reference gauge at least 4 times more accurate
• Adapters, seals and tools for the gauge connection

7. Prerequisites

• Gauge removed under permit, cleaned of process fluid.
• Gauge visually checked: glass, pointer, dial and connection undamaged.

8. Procedure

8.1 Setup

1. Mount the gauge vertically (its normal position) next to the reference.
2. Exercise the gauge to full scale and back to zero three times.

8.2 Test

1. Check the pointer at zero with no pressure applied.
2. Apply 0, 25, 50, 75 and 100 % of full scale upscale, tapping the gauge lightly before reading.
3. Return downscale through the same points without overshooting.
4. Record readings and calculate error and hysteresis in % of span.

8.3 Adjustment

1. If zero is out, reset the pointer (adjustable pointer or micrometer pointer).
2. If span or linearity are out, adjust the movement if the design allows; otherwise replace the gauge.
3. Repeat the test after adjustment.

9. Acceptance Criteria

• Error and hysteresis within the accuracy class at every point.
• Pointer returns to zero.

10. Records

Related tools

This is a generic procedure. Adapt it to your site permit system, the manufacturer instructions and your quality system before use.

Frequently Asked Questions