How to install a small capacitor measuring gear on a multimeter

When using an ordinary multimeter with the R×1kΩ range to measure a larger capacitor, the charge and discharge are more obvious, so it is more practical to judge the quality of the capacitor more intuitively. Experienced amateur electronics enthusiasts can also judge the approximate range of the capacitor. However, for small capacitors with a capacity below 0.01μF, it is difficult to observe the swing of the meter pointer using this measurement method, so it is impossible to judge the quality of the measured capacitor. Here we introduce how to cleverly switch the capacitor measurement range of the multimeter. This is achieved by using a Darlington tube and a double-pole double-throw switch to add an additional circuit to the multimeter. The principle is shown in the figure.

In the figure, VT1 and VT2 are NPN silicon triodes 9013 or 3DG4, 3DG6 and other triodes, and their β is required to be ≥ 60. Here they are connected as Darlington tubes (i.e. composite tubes, so that their amplification factor is β·β). Its working voltage is provided by the 1.5V battery of the multimeter. The amplification effect of VT1 and VT2 is used to increase the swing amplitude of the meter pointer when the small capacitor being measured is charged and discharged. Under normal circumstances, the swing of the meter pointer during charging can be observed for capacitors with a capacity of more than 10pF. When connected, on the contact below the double-pole double-throw switch S. When
in use, when the switch S is turned to the "capacitance measurement" position, the red test lead and the black test lead can be used to measure small capacitors; when S is turned to "normal", it can be used for normal use. When
making, S can use a small 2×2 toggle switch (also called band switch KBB-2×2) or a small boat switch.