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 capable of measuring a feature within its specified tolerance limits.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( PTR \) — Precision-to-Tolerance Ratio (dimensionless)
• \( P \) — Precision of the measurement system (in same units as tolerance)
• \( T \) — Tolerance of the feature being measured

Explanation: The precision of the measurement system is divided by the tolerance to determine what proportion of the tolerance is consumed by measurement uncertainty.

3. Importance of PTR Calculation

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

4. Using the Calculator

Tips: Enter the measurement system's precision and the feature's tolerance in consistent units. Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a good PTR value?
A: Typically, PTR ≤ 0.1 (10%) is recommended, though some applications may accept up to 0.3 (30%).

Q2: How is precision (P) determined?
A: Precision is often estimated as 6 times the standard deviation of repeated measurements (6σ).

Q3: What if my PTR is too high?
A: A high PTR suggests your measurement system consumes too much of the tolerance. Consider improving measurement methods or equipment.

Q4: How does PTR relate to GR&R?
A: PTR is a simpler alternative to Gage R&R, focusing specifically on the relationship between measurement precision and tolerance.

Q5: Can PTR be greater than 1?
A: Yes, but this indicates the measurement system's precision exceeds the tolerance, making meaningful measurement impossible.