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D2525-22 – Standard Test Method Technical Guide
📐 Scope and Sampling Units
This practice, issued under the fixed designation D2525 −22, covers the design of a sampling plan to be used for the determination of moisture content in various forms of wool. The scope explicitly includes grease wool, scoured wool, carded wool, garnetted wool, wool top and intermediate products, and rovings.
The standard provides specific directions for the designation of sampling units, the calculation of the number of sampling units required to achieve a preselected precision and confidence level, and methods for calculating confidence limits for the mean based on the variability of the sample tested.
| 🟦 Referenced Document | 📏 Role within D2525 Framework |
|---|---|
| D1576 | Test Method for Moisture in Wool by Oven-Drying |
| D2462 | Test Method for Moisture in Wool by Distillation With Toluene |
| E122 | Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process |
| D1060 | Practice for Core Sampling of Raw Wool in Packages for Determination of Percentage of Clean Wool Fiber Present |
| D4845 | Terminology Relating to Wool |
⚙️ Key Statistical Requirements and Procedure
The practice outlines a two-pronged approach. The user can either calculate the number of sampling units required to give a preselected allowable variation at a stated probability level, or calculate the confidence limits for the sample mean obtained for a given size of sample. Correct probability statements about the relationship between the sample mean and the population mean require strict adherence to the defined conditions.
🎯 Statistical Foundation: The standard requires a deliberate act of randomization so that all potential sampling units have approximately the same chance of being taken. This ensures unbiased, representative samples for the moisture determination.
| 📐 Parameter | 🎯 Specification / Use Case |
|---|---|
| Allowable Variation | Preselected by the user based on specific precision requirements |
| Probability Level | Typically integrated from Practice E122 (e.g., 90% or 95% confidence) |
| Sampling Unit | Defined by subdividing the lot with unique identification |
| Insufficient Variability Data | Confidence limits for the mean can still be calculated directly from the sample |
📊 Integration with Test Methods and Terminology
The sampling plan devised by this standard is specifically intended for use in connection with Test Method D1576 (Moisture in Wool by Oven-Drying) or Test Method D2462 (Moisture in Wool by Distillation With Toluene). The correct application of these test methods on the samples obtained via D2525 is essential for generating valid moisture content results. Decision on which specific sampling units constitute the required lot sample ensures all units have an approximately equal chance of being selected.
💡 Important Distinction: While Practice D1060 covers core sampling of raw wool for clean wool fiber present, this standard (D2525) focuses exclusively on the statistical sampling plan for moisture content determination. Do not confuse the two objectives.
❓ Frequently Asked Questions
🔍 What forms of wool does the scope of D2525 cover?
The practice covers grease wool, scoured wool, carded wool, garnetted wool, wool top and intermediate products, and rovings.
💡 How does the standard ensure a valid probability statement?
It requires a deliberate act of randomization, giving all potential sampling units an approximately equal chance of being selected for the lot sample.
⚡ Can I calculate sample size if I have no prior data on variability?
Yes. If insufficient information about the variability of the sampling units is available, the standard provides directions for calculating confidence limits for the sample mean directly from the variability observed in the tested sample.
📌 What test methods are used in conjunction with this sampling practice?
The sampling practice is intended for use with Test Method D1576 (oven-drying) or Test Method D2462 (distillation with toluene) to determine the moisture content.