GENERAL. a. The Model 6105 Resistivity Adapter is a guarded test fixture for measuring volume and surface resistivities of materials when used with a regulated power supply and an electrometer. The complete system permits measurement of volume resistivity from 10³ to 3 x 10¹⁹ ohm-cm and surface resistivity from 10³ to 5 x 10¹⁸ ohms, in accordance with procedures of the American Society for Testing and Materials. The Adapter can accommodate samples up to 4 inches in diameter and 1/4 inch thick with excitation voltages up to 1000 volts. b. The Model 6105 has been designed to minimize measurement error. The electrode configurations conform to the ASTM recommendations for measurement of electrical resistance of insulating materials. The test sample is shielded to prevent stray pickup. The guard ring circuit is arranged to minimize leakage currents from the measuring circuit. Uniform pressure is always applied over the measuring area, because the test sample is held between the spring-loaded, guarded electrode and the one-pound test weight assembly. Due to these considerations, measurement accuracy depends primarily upon the accuracy of the voltage source and the electro meter. c. Recommended instruments for use with the Model 6105 are the Keithley Model 240A Regulated High Voltage Supply and the Keithley Model 610C Multi-Range Electrometer. The Model 240A provides excitation voltages up to 1200 volts in calibrated one-volt steps. Its output is accurate within 1%. The Model 610C provides direct reading current ranges to 10⁻¹⁴ ampere full scale. Its accuracy is ±2% of full scale to 10⁻¹¹ ampere, and ±4% of full scale beyond. Although the Model 240A and the Model 610C are the recommended instruments for use with the Resistivity Adapter, the Model 6105 is compatible with all Keithley high voltage supplies and electrometers.