1. What is Precision-to-Tolerance Ratio (PTR)?

Definition: PTR is a dimensionless ratio that compares the precision of a measurement system to the tolerance of the feature being measured.

Purpose: It helps determine whether a measurement system is adequate for inspecting a particular tolerance.

2. How Does the PTR Calculator Work?

The calculator uses the formula:

Where:

• \( PTR \) — Precision-to-Tolerance Ratio (dimensionless)
• \( P \) — Precision of the measurement system (mm)
• \( T \) — Tolerance of the feature being measured (mm)

Explanation: The precision (typically 6 times the standard deviation of measurement variation) is divided by the tolerance to determine the ratio.

3. Importance of PTR Calculation

Details: A lower PTR indicates better measurement system capability. Industry standards often recommend PTR ≤ 0.1 (10%) for critical measurements.

4. Using the Calculator

Tips: Enter the measurement system precision and feature tolerance in the same units (typically mm). Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a good PTR value?
A: Generally, PTR ≤ 0.1 (10%) is recommended, though some industries may accept up to 0.3 (30%) for non-critical features.

Q2: How is precision determined?
A: Precision is typically calculated as 6 times the standard deviation of repeated measurements of a reference standard.

Q3: What if my PTR is too high?
A: A high PTR suggests your measurement system isn't precise enough. Consider using more precise equipment or widening tolerances if possible.

Q4: Can PTR be greater than 1?
A: Yes, but this indicates your measurement variation exceeds the tolerance, making the measurement system unsuitable for inspection.

Q5: How does PTR relate to GR&R?
A: PTR is a simpler alternative to Gage R&R, providing a quick assessment of measurement system adequacy relative to tolerances.