Digital Multimeters

This is because the input impedance for mV measurement is high, typically at a level of GΩ, leading a strong drive capability to the voltage source. On the condition that the test leads are open, the induced voltage generating from ambient electromagnetic wave can easily be detected by the multimeter when performing mA DC or mV AC measurement, thus, it is normal that the displayed value can not be reset. The displayed value can be reset if the test leads are shorted.

The accuracy is typically denoted in the percentage form of the reading, that is 1% of the reading, for example, if the measured value is 100V, the actual value may be between 99V~101V. But for technical parameters, the least significant digit will be counted into the accuracy, for example, if the accuracy is ±(1%+2) and the measured voltage is 100V, the actual value will lie between 99.8 and 101.2V.

Ture RMS is a representation of non-normal AC signal.
Average Response Measurement: The average value multiplies by the waveform factor to obtain the value of AC signal.
True-RMS Measurement: The value of AC signal is obtained by the root mean square algorithm. For pure sine wave, accurate measurement can be achieved by average response or True-RMS; while for distorted waveforms or general non-sine waves such as square wave, triangular wave, sawtooth wave, an accurate measurement can be obtained by True-RMS only.

The audion (Q1) at the PCB is broken down. Please send the product to the manufacturer for maintenance.

1. Check if the USB function is started (There is symbol indication on the LCD)
2. Check if the software version supports the operating system.
3. Connect with other computers to check if the operating system is incompatible with the software.

Poor contact of conductive adhesive at LCD screen due to impact or bumping. (Apply new conductive adhesive or send the product to the manufacturer for maintenance)

The multimeter is protected by the fuse at current gear, it is also protected at voltage gear as it is able to detect voltage of 1000V and designed with internal resistance of 10MΩ. There is no fuse protecting the multimeter at resistance gear since voltage excitation source exits at resistance gear, the measured resistance is detected by detecting the current flowing through the measured resistance, if the voltage is measured at resistance gear, two voltage sources will crash, which may cause damage to the multimeter at resistance gear. Overload-protection circuit is also designed for the multimeter.

The copper wire of the test lead may be broken, please replace the test lead with new one. Note: Do not twist the test leads.

Generally, the specification of frequency accuracy is applicable to above 5% or 10% of the range, if below 5% or 10%, the accuracy will be affected, the affected value and the starting value of the range changes upon the models of products. For nonsinusoidal waveform measurement, please select a True-RMS meter and be sure that the range of duty cycle is 1%~99%.

It is generally difficult for multimeter to detect burr signal in AC signal, as what multimeter detects is the value at a certain time point. When the multimeter converts digital to analogue, the sampling point may not be the burr peak, so the test result can not reflect whether there is burr in the waveform signal. For detection by oscilloscope, what detects is continuous waveform generally, and the MAX/MIN value can be captured through oversampling, thus the burr signal will be displayed.

The MCU control chip is damaged, please send the multimeter to manufacturer for maintenance.

Because the air is moist and the moisture content in the vaseline applied on the PCB pad increases. Please wipe out the vaseline on the PCB pad and apply new vaseline, or perform measurement when the air is dry.