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However, for measuring current, additional ports are provided. It is the inclusion of milliampere current port that requires a good protective circuitry in the multimeter, as accidental high current applications can damage the instrument and cause harm to the user as well.
Placed between the battery and the input ports, the fuse acts as circuit protector cutting the measuring process off when inputs higher than bearable range are applied on the multimeter. The battery and fuse are closed by a flap using just a single screw so that they can be easily changed avoiding longer interruptions in measuring process. An extra fuse is provided for convenience purposes. Internal Structure Fig. The PCB and all the circuitry are mounted upon the upper sectionwhile the lower section is a thin layer of anodized aluminum.
This non conductive layer aids in uniform heat dispersalin cases of high current inputs to the multimeter. PCB Fig. This IC has quad input and outputs and requires only a single power supply. Thus it delivers optimized power at low voltage inputs.
This IC is mainly used as logical comparator and parity checkers. Working on a medium power requirement, this inverter IC takes 30ns to change its output from low to high and vice versa.
Also, the contacts for switching the multimeter on and off can be seen. Some multimeters employ the rotary switch to handle the switching ON and OFF options while some require a slider switch, like the one in this insight.
The other side of the PCB has 11 concentric conducting rings among which connections are made and broken with the help of the rotary knob that functions as a switch. The pattern of the rings can vary depending on the multimeter manufacturer and the functions listed. None of the rings completes a complete circular pattern but are broken from some part or other. These lines are also greased so as to allow smooth run of the switch when it is rotated. The rotation of the switch defines which part of the circuit on the PCB would be active and which would be not.
As a matter of fact, the rotary switch does not necessarily make contact with the rings corresponding to the function they are placed near to.
For instance, when the multimeter is actuated to measure resistance in the range of K, the placement of the contacts of the switch can be seen in the images shown below: Fig. The metal leafs at the bottom of the dial act as jumper shorts which establish interconnections between different pairs of conducting rings at each position. The connection between the rings conveys an electric signal to PCB regarding the quantity and its respective range to be measured Fig.
The use of tiny metal balls over a corrugated track also makes the dial and hence the multimeter mode stays in position even if it the setup shakes or the multimeter is dropped. LCD Fig. Since LCD output is a direct measure of resolution of the multimeter, it is desired to have it show as many characters as possible.
Display of the LCD is measured in number of digits it can show. Total numbers that can appear on the LCD are defined as counts. The resolution of the LCD is defined by the number of counts along with the most significant digit.
Insight – How Digital Multimeter Works
cd4069中文资料详解（cd4069引脚图及功能_工作原理_内部结构及应用电路） - 全文
Original logic chip IC HCF4069UBE HEF4069/HCF4069 15V DIP14