Method for measuring the value of high resistance with a pointer multimeter.
Ordinary pointer multimeter, such as MF47, has only Rx10k electric barrier. When measuring the high resistance value of several megaohms, it is difficult to read because the angle of pointer swing is not large. In this case, the following workarounds can also be used to measure high resistance with a pointer multimeter.
1.A circuit for measuring high resistance using a pointer multimeter is shown in figure 1. Fig. 1 (a) is an expansion measurement circuit with NPN low power transistor, and fig. 1 (b) is an expansion measurement circuit with PNP low power transistor. Due to the amplification of the transistor, the equivalent resistance between A and B is less than that indicated by the Rx, pointer of the measured resistance, R is only-(K > 1) of the Rx, and its relation is as follows.
The K in the above formula is not the amplification signal number B of the transistor, but is related to B, K < B. And K will vary with the swing angle of the meter needle, which is mainly caused by the non-linearity of the electric blocking scale of the pointer-type multimeter and the nonlinearity of the transistor.
When the Rx= 33M0 is measured, the indicator value of the watch needle is R = 335kq; when the Rx=8.2M0 is measured, R = 108kq; and when the Rx=1. Is measured, when the transistor is used, the value of the meter is 335kq. When SMO, R=25kn. The K values corresponding to the above three different positions are 97, 76 and 60, respectively.
2, the detection method.
According to the above-mentioned method, the dial scale (about 90 °) can be classified into 5 equal parts, each of which is 18 °. The K value of each 18 °area can be determined by experiment first. In this way, when measuring the Rx, the value of the measured resistance can be obtained by multiplying the R of the area in which the stylus is located by the corresponding K value.
Although the above-mentioned method of measuring high resistance has some errors, but because the method is simple, it is more practical to measure and estimate the leakage of electricity in this part or component.