Definition:
Accuracy is the degree to which the flowmeter’s reading matches the actual flow rate. It is usually expressed as a percentage of:
- Reading (RD) – more precise at higher flow rates.
- Full Scale (FS) – used for simpler systems; less accurate at low flows.
- Span – the difference between maximum and minimum measurable flows.
Example:
If a flowmeter has an accuracy of ±1% of reading, and the actual flow is 100 GPM, the meter will read between 99 and 101 GPM.
Note: Accuracy may vary depending on fluid type, temperature, and installation conditions.
Flowmeter Repeatability
Definition:
Repeatability measures the meter’s ability to provide consistent readings under the same conditions over multiple tests. It is typically tighter than accuracy (e.g., ±0.1% vs. ±1%).
Why It Matters:
High repeatability ensures reliable trend data and process control—even if the meter isn’t perfectly accurate.
Example:
If a flowmeter shows 100.2, 100.3, and 100.1 GPM under identical conditions, it has good repeatability.
Flowmeter Rangeability (Turndown Ratio)
Definition:
Rangeability is the ratio between the maximum and minimum flow rates that a meter can accurately measure.
Formula:
Rangeability = Maximum Flow / Minimum Measurable Flow
Example:
A flowmeter with a rangeability of 100:1 can measure from 1 GPM to 100 GPM with reliable accuracy.
Importance:
Wide rangeability is critical in applications with variable flow, such as batch processes or systems with seasonal load changes.
Summary Table
| Parameter | Definition | Typical Value | Importance |
| Accuracy | Closeness to true flow value | ±0.1–2% of reading | Ensures flow measurement meets spec |
| Repeatability | Consistency of readings at same conditions | ±0.05–0.2% | Essential for reliable trend analysis |
| Rangeability | Effective measurement range | 10:1 to 1000:1 | Allows accurate readings over wide flows |
