Pressure Gauge Markings, Accuracy & Range Selection – Practical Engineering Guide
This technical guide explains pressure gauge markings, EN 837-1 standard, accuracy classes, oversized gauge effects, and correct range selection rules. It is intended for instrumentation engineers, technicians, automation professionals, and engineering students working in industrial plants.
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1. EN 837-1 Pressure Gauge Standard
EN 837 is a European standard governing mechanical pressure gauges. EN 837-1 applies specifically to Bourdon tube pressure gauges, the most widely used type in industry.
This standard defines:
- Mechanical construction requirements
- Safety features (blow-out back, solid front)
- Accuracy classes & permissible errors
- Pressure testing procedures
- Material durability requirements
2. Accuracy Class (CL)
Range: 0–100 bar
Accuracy: CL 1.0 → ±1% FS
Maximum Error = ±1 bar
Accuracy: CL 1.0 → ±1% FS
Maximum Error = ±1 bar
Important: Accuracy is based on FULL SCALE value.
3. Effect of Oversized Gauge Range
0–100 bar gauge (CL 1.6)
Error = ±1.6 bar
Low pressure = Higher relative error.
Error = ±1.6 bar
Low pressure = Higher relative error.
4. Practical Gauge Range Selection
Golden Rule: Operating pressure should be 60–70% of full scale.
- Process pressure ≈ 10 bar
- Best: 0–16 bar
- Acceptable: 0–25 bar
- Avoid: 0–100 bar
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Quick Formula:
Gauge Range ≈ 1.5 × Operating Pressure
Gauge Range ≈ 1.5 × Operating Pressure
5. Common Industrial Mistakes
- Oversized gauges causing wrong readings
- Undersized gauges damaging instruments
- Ignoring vibration/pulsation
- Wrong wetted material
- No calibration schedule