Features of the Digital Multimeter and the Dual Impedance Digital Multimeter
The basic composition of an ordinary digital multimeter is shown in the figure. Double integral A/D converter is the "heart" of the digital multimeter, through which the analogue - digital conversion. Peripheral circuits mainly include function converter, function and range selector switch, LCD or LED display, in addition to the buzzer oscillator circuit, drive circuit, detection line on and off circuit, low voltage indicator circuit, decimal point and sign (polarity sign, etc.) drive circuit.
A/D converter is the core of the digital multimeter, using a monolithic large-scale integrated circuits 7106. 7106 using the internal heterodyne gate output, can drive the LCD display, power consumption is extremely low. Its main features are: a single power supply, and a wide range of voltages, the use of 9V stacked battery to achieve miniaturisation of the instrument, high input impedance, the use of internal analogue switches to achieve automatic zero and polarity conversion. The disadvantage is that the A/D conversion speed is slow, but can meet the needs of conventional electrical measurements.
Basic knowledge of impedance
The vast majority of digital multimeters sold on the market today for measuring industrial, electrical, and electronic systems have very high input loop impedances, generally greater than 1 megohm. This simply means that when the DMM is measuring a loop, it will have little or no effect on the performance of the loop. This is what is needed for most measurement needs, especially for more sensitive electronic or control loops. Previously used troubleshooting tools such as analogue multimeters and solenoid testers typically had low impedance input loops of around 10 kOhm or less. Although such tools are not affected by stray voltages, they are only suitable for measuring power circuits or other applications where low input impedance will not adversely affect or alter the performance of the circuit.
Given the complexity and diversity of measurement and testing needs in most facilities today, dual-impedance input instrumentation provides the troubleshooter or technician with greater flexibility to meet a wide range of application or measurement needs, from basic voltage testing to troubleshooting sensitive electronic circuits. In addition, the instrument's voltage detector helps increase efficiency and provides an additional barrier before starting work in control cabinets or other areas where voltage may be present.
The Dual Impedance Input Meter provides the troubleshooter or technician with greater flexibility for applications or measurements ranging from basic voltage testing to troubleshooting sensitive electronic circuits. In addition to this, the voltage detector built into the meter helps to increase efficiency and adds another barrier before starting work in control cabinets or other areas where voltage may be present.
