Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D4949-94 – Standard Test Method Technical Guide
📐 Test Overview and Scope
This test method describes the procedure for determination of both surface and volume (bulk) d-c resistivity of writing paper. It is specific to the Keithley 6105 resistivity adapter and has been developed for writing papers processed in high-speed nonimpact printers where resistivity control is critical. Paper generally is considered a material with good insulating characteristics, but control of resistivity to within specified limits is important in certain applications. This standard does not purport to address all safety concerns; it is the user’s responsibility to establish safety practices.
⚙️ Test Procedure and Equipment
A paper specimen is placed between appropriate metal electrodes. An electrical voltage is applied for a fixed period of time, and the resultant current is measured accurately. By using appropriate electrodes, surface and volume resistance can be measured separately. From this information, both surface and volume resistivity are calculated.
This test method is specific to the Keithley Model 6105 resistivity adapter. The precision statement was based on the use of that instrument. Studies have shown that results vary depending on the type of resistivity adapter used, and for reproducibility between laboratories, it is essential that the same model be used.
📊 Key Definitions and Calculations
| 🟦 Term | 📐 Definition |
|---|---|
| Surface Resistivity | The ratio of the potential gradient parallel to the current along the surface to the current per unit width of the surface. |
| Volume Resistivity | The ratio of the potential gradient parallel to the current in the material to the current density. |
Surface resistivity is numerically equal to the surface resistance between two electrodes forming opposite sides of a square, where the size of the square is immaterial.
⚠️ Technical Note: For accurate interlaboratory comparisons, always use the Keithley 6105 resistivity adapter as specified. Variation in adapter type can lead to significant differences in results.
❓ Frequently Asked Questions
🔍 What is the main purpose of D4949-94?
To determine the d-c resistivity (both surface and volume) of writing paper, especially for high-speed nonimpact printers where resistivity control is critical.
💡 Why is this method specific to the Keithley 6105?
Because the precision and reproducibility are based on this instrument, and using different adapters can cause variability in measurements.
⚡ How is resistivity calculated from this test?
By measuring the current after applying a voltage for a fixed time, resistance is obtained, and from electrode dimensions, surface and volume resistivity are calculated.
📌 Is this method in conflict with ASTM D 257?
No, it is a specialized test for writing papers and is not in conflict with Test Methods D 257 for general insulating materials.