Electrometer resistance measurement

This is probably caused partly by the fact that no satisfactory theory is available for interpreting the data obtainable from current measurements during and after irradiation, partly by the experimental difficulties involved in using sensitive electrometers and high resistance measuring cells required for the measurements. 

IV. Keithley electrometer to measure the electrical resistances of pure polymers and their blends cast films (thickness of each sample, 6.0 pm) on microscope slides (6.25 cm X 0.1 cm), based on the two-probe method [1] and four-probe Van der Pauw technique [1-2]. 

The electrometer bandwidth characterizes the ac frequencies the electrometer can measure when it is driven from a low-impedance source. The electrometer bandwidth must be higher than the bandwidth of the rest of the potentiostat electronics. The electrometer input capacitance and the reference electrode resistance form an RC filter. If this filter s time constant is too large, it can limit the effective bandwidth of the electrometer and cause system instabilities. Smaller... 

If the sample shown in Figure 2.4 is to be tested, two electrodes would be connected to two terminals of an electrometer to measure E and I or just R (resistance). 

The preferred potential-measuring instruments are potentiometers or electrometers, either of which permit measurements to be made without flow of sufficient current to polarise the electrodes during the determinations. It is also possible to use millivoltmeters if the internal resistance of the instrument is high enough to avoid any appreciable flow of current. 

The magnitude of AV is measured most conveniently by placing an air electrode (a radiation emitter Po210 [alpha-emitter]), near the surface (ca. millimeter in air), connected to an impedance electrometer. This is required since resistance in air is very high, but it is appreciably reduced by the radiation electrode. However, proper isolation is essential for the data to be reliable. 

The direct-current (DC) volt-ampere (V-A) characteristics were measured with a microcomputer-controlled Keithley 617 electrometer in the temperature range 10 to 60 °C. From linear part of V-A dependences the resistance ffl - U/I was determined [32], where U is the voltage on the needle electrodes and I is the current passing through the sample. 

D.c. resistance is measured by a high impedance electrometer (Vibron Electrometer 33B). 

Mechanical conditioning can greatly affect the measured resistivity but the effect of deformation is not entirely permanent and recovery can be accelerated by heating. For this reason, ISO 1853 specifies conditioning at 70°C, followed by conditioning at 23 °C and 50% RH without disturbance of the test piece. The potentiometric electrodes are shown in detail and sources of a suitable electrometer given in an annex. The potential of the current... 

If both electrode processes operate under standard conditions, this voltage is E°, the equilibrium standard electrode potential difference. Values of E and E° may be conveniently measured with electrometers of so large an internal resistance that the current flow is nearly zero. Figure 3.1.6 illustrates the measurement and the equilibrium state. The value of E° is a most significant quantity characterizing the thermodynamics of an electrochemical cell. Various important features of E and E° will be addressed in the following chapters. 

If we take into account the finite input resistance Rm of any real electrometer, we recognise that any reading of a probe potential will decay exponentially with a time constant RmCm. If is of the order of 10 pF (it cannot be made high otherwise Vm will be too small to measure) the input resistance must be kept above about 1013 fl to keep the time constant long compared with the time required to take a reading. 

---