## Measurement of High Ohmic Value Resistors

High ohmic valued chip resistors exhibit characteristics of both insulators and normal resistors. As a result, a chip resistor may have a significant voltage coefficient of resistance, i.e., the resistance may vary with the applied voltage. This mandates that a fixed voltage source rather than a fixed current source be utilized when measuring these devices. Resistances can then be computed as volts/amperes. The applied voltage for a high ohmic value chip resistor is often specified as appropriate for the application to assure correlation. Typical values of applied voltage are 1 and 5 volts DC. This requirement leads to the measurement of very low currents and the attendant problems of such measurements. The problems of low current measurements include: 1. Noise currents generated in the connecting cables when flexed (triboelectric effect) 2. Noise from sources other than the cables 3. Cable, fixture and probe leakage currents 4. Cable, fixture and other stray capacitances 5. Radio Frequency Interference (RFI) 6. Characteristically high Temperature Coefficients of Resistance (TCRs) These problems can be minimized by: 1. Properly connecting the resistor to the measurement system. 2. Properly guarding and shielding to reduce or eliminate electrostatic noise. IMS recommends that all meters be calibrated to [...]