All You Need to Know About Pressure Gauge Accuracy Grades
1. How Accurate Do You Need ?
Gauge accuracy is one of the factors in determining the best pressure gauge for your application.
Accuracy always has a cost. The more accurate the gauge, typically the more expensive. Lack of accuracy can cost even more if the quality of the end process result suffers.
The most important thing to consider when determining your accuracy needs are the engineering requirements of your process and any applicable regulatory requirements. But, for a starting point, these are some industry recommendations
Test Gauges and Standards
0.25% through 0.10% full-scale accuracies
0.5% full-scale accuracy
General Industrial Processes
Less Critical Commercial Processes
2. What Is ±3-2-3% of Span Accuracy?
Accuracies on gauges are typically listed as a grade like B or 2A or written as ±3-2-3% of span accuracy.
These ratings come from two charts that are often considered the standard in grading accuracy, the ASME B40.1 for dial-type gauges and the ASME B40.7 for digital gauges.
3. What’s the Difference in the Grades and Spans?
The grades are shorthand assignments to the accuracy span in that grade. The accuracy span percentage is based on the the entire range of the gauge. So 1% of a 100psi gauge is 1psi and 3% of a 300psi gauge is 9psi. The smaller the percentage in the accuracy rating the more accurate the reading is.
Example: 100psi Pressure Gauge
±1% of span accuracy
Never more than 1 psi over or under the pressure reading in ideal conditions .
±0.1% of span accuracy
Never more than 0.1 psi over or under the pressure reading in ideal conditions.
±3-2-3% of span accuracy
Accuracies with multiple percentages indicate that the accuracy varies at different reading points on the gauge. These types of gauges are most accurate in the middle half of their range. So then margins of error on our 100# pressure gauge would be:
- 3psi or ±3% for 0-25 psi range of the gauge
- 2psi or ±2% for 26-75 psi range of the gauge
- 3psi or ±3% for 76-100 psi range of the gauge
4. A Form Can Make You Understand Better
For example, a 10 bar pressure gauge with measuring accuracy class 4 may deviate across the entire measuring range by ± 4% (± 0.4 bar).