What is the cause of resistivity test are not accurate

Adjustable resistor is a kind of adjustable electronic components. It is formed by a resistor and a rotating or sliding system. When the resistance between two fixed electric shock, plus a voltage by rotating or sliding system change the location of the contact on the resistor body, between the fixed contact and moving contact can be a relationship with the moving contact position with a certain voltage. It is mostly used as a divider, the encoder is a four-terminal element. Encoder is basically a slide rheostat, there are several kinds of style, commonly used in speaker volume switch and laser power size adjustment. So, what are the cause of resistivity test are not accurate? Electronic give you summed up as follows. Cause a medium material, test voltage resistance ( Rate) Value generally cannot keeps the same wide voltage range, namely the ohm's law is not applicable. Under the condition of normal temperature, within the scope of the low voltage, electrical current increases linearly with the increase of the applied voltage, resistance of materials remain the same. After more than a certain voltage, due to the ionization motion increases, the increase of the electric conduction current far faster than test voltage increase, material of resistance lower quickly. Thus, plus the test voltage is higher, the lower the resistance of materials, so that testing materials under different voltage resistance may have bigger difference. It is worth noting that lead to material resistance determinants of change is a test of the electric field intensity, rather than test voltage. The test voltage for the same, if the distance between the test electrode is different, the testing results of material resistivity will also be different, the smaller the distance between the positive and negative electrodes, test values. Reason two, interference after high insulation and dc voltage, by sample of current is very small, vulnerable to the influence of outside interference, cause larger test error. Thermoelectric potential and contact potential is generally small, can be ignored. Electrochemical potential is mainly produced by wet samples with different metal contact, only about 20 mv, moreover in the static test requirements of relative humidity is low, in the dry environment test, can eliminate potential electrolysis. Therefore, the interference of stray current is coupled or electrostatic induction electric potential. The test current is less than 10 - 10 a or above 1011 ohm resistance measurement; Are test samples, test electrode and the test system are strict screening measures should be taken to eliminate the effects of interference. Three reasons, the test time pressure with a dc voltage to be measured materials, the material being tested is not instantaneous current reach a stable value, but a decay process. In pressure at the same time, through the larger charging current, then it is a long time slowly reduce the absorption of current, finally achieve steady electrical current. Measured resistance value is higher, the longer the equilibrium time is. Accordingly, when measured in order to correctly read the measured resistance value, should be read after stable numerical or reading value of pressure after 1 minute. In addition, high insulation resistance value but also to the history of charged. Materials for accurate evaluation of electrostatic properties, resistance to material ( Rate) Test, should be first to eliminate electric processing, and let stand for a certain amount of time, the incubation time may take 5 minutes, and then, again according to measurement procedure test. In general, the test of a material should randomly at least 3 ~ 5 samples for testing, to the average as test result. The reason of four ordinary materials, environmental temperature and humidity resistance decreases with the increase of environmental temperature and humidity. Relatively, the surface resistance ( Rate) Humidity is sensitive to the environment, and the body resistance ( Rate) Is sensitive to temperature. Humidity increases, the surface leakage increase, the body electric conduction current will increase. Temperature, the movement of the carrier rate is accelerated, the absorption of dielectric materials and conductance current will increase, according to relevant data, in a normal medium 70 C when the resistance value of only 10% of the 20 C. Therefore, when measuring the resistance of the material, must indicate the sample balance with the environment temperature and humidity. Reason five leakage in the test, test equipment, circuit insulation resistance is not high in attachment, tend to improperly and the sample under test, such as sampling resistor in parallel, can bring great influence the measurement result. Therefore to reduce the measurement error, should adopt protection technology, installed on the leakage current of line protection, the conductor to basically eliminate the influence of the stray current is the result of the test; High voltage line-to-line ionization on the surface, of a leak, so try to use high insulation, large wire diameter of high pressure wire as high voltage output line and try to shorten the wires, reduce tips, put an end to the corona discharge; Use the insulation materials such as polyethylene, ptfe test bed and to support the body, to avoid the test value is low due to this reason. Taken together, these factors could be the cause of resistivity is not accurate. 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