Introduction to the main indicators, display digits and display characteristics of digital multimeters
The display digits of a digital multimeter are usually 3 1/2 to 8 1/2 digits. There are two principles for judging the display digits of digital instruments: one is that the digits that can display all numbers from 0 to 9 are integer digits; The numerator is the numerator, and the count value is 2000 when the full scale is used, which indicates that the instrument has 3 integer digits, and the numerator of the fractional digit is 1, and the denominator is 2, so it is called 3 1/2 digits, read as "three and a half digits ", the highest bit can only display 0 or 1 (0 is usually not displayed). 3 2/3 digits (pronounced "three and two-thirds digit"), the highest digit of the digital multimeter can only display numbers from 0 to 2, so the maximum display value is ±2999. Under the same conditions, it is 50% higher than the limit of a 3 1/2 digit digital multimeter, which is especially valuable when measuring 380V AC voltage.
Popular digital multimeters generally belong to handheld multimeters with 3 1/2 digits display, and 4 1/2, 5 1/2 digits (less than 6 digits) digital multimeters are divided into handheld and desktop. More than 6 1/2 digits mostly belong to desktop digital multimeters.
The digital multimeter adopts advanced digital display technology, with clear and intuitive display and accurate reading. It not only ensures the objectivity of the reading, but also conforms to people's reading habits, and can shorten the reading or recording time. These advantages are not available in traditional analog (ie pointer) multimeters.
The principle and standard of on-off gear of multimeter
The on-off position is a measurement mode that almost all multimeters have, and is used to measure whether the line is on or off (short circuit). Generally, a buzzer and an LED light are used. The buzzer sounds or the LED light turns on, indicating that the circuit is connected. As shown in the figure, the sign in the red box is the on-off gear of the multimeter.
On-off gear principle
When the multimeter is turned to the on-off position, the internal circuit that is connected is: the black test lead is connected to the negative pole of the internal battery, the positive pole of the battery is connected to a resistor with a small resistance, and the other end of the resistor is connected to the red test lead. The internal chirping circuit gets the trigger signal from the resistor. If the two test leads are short-circuited or the resistance between them is small, then the voltage on the trigger resistor inside the meter is high, thus triggering the beep. If the resistance between the two test leads is large, then the divided voltage of the internal trigger resistor connected in series is very small, and the beep cannot be triggered.
On-off file standard
The general definition is that 80 ohms and below are conduction, otherwise it is non-conduction. That is to say, connect the red and black test leads of the multimeter to both sides of a line. If the resistance of this line is lower than 80 ohms, the multimeter will make a sound and think that this line is conducting.
