The Tips to Measure High Megohm Resistors

Resistance value is 1 GΩ or higher resistors often called high megohm resistors. High megohm resistors make these components become unusual devices. So in the measurement, we want to consider the following factors: voltage coefficient and temperature coefficient, mechanical vibration effect and pollution, etc.

The extensive use of high megohm resistor has two kinds: carbon film resistors and metal oxide resistors. Compared with ordinary resistors, high carbon film megohm resistance has big noise, high temperature coefficient, and high voltage coefficient and it’s instable and very fragile. The development of metal oxide type resistors in recent years made voltage coefficient greatly reduced, the temperature coefficient and time stability are also improved. The modern devices can achieve voltage coefficient is less than 5 PPM/V, after five years of testing, it has no obvious drift. 100 M Ω temperature coefficient is in 0.01% / ℃, 100 G Ω temperature coefficient is in 0.025% / ℃.

Dealing with this sort of resistors should be very careful. Due to conductive materials particles movement caused by mechanical vibration, it may greatly change resistance value. It is very important not to touch the resistance components or the glass shell. If we do so, it will produce new current access or a few of electrochemistry will produce electric current, and it may change its resistance value.

The resistors are coated to prevent water film forming on the surface. So, if the careless handling or air pollutants in sedimentary and forming on the surface film, it should use bubble sign dipped the methanol to clean. After cleaning, we shall make the resistor dry for several hours in low humidity in the air, thus to make static electricity to dissipate.