Weak current College】 【common mode and differential mode knowledge】.

What is the common mode interference and differential mode interference
Voltage and current changes through wire transfer when the second form, we will which is called "common-mode" and "differential mode". Equipment of the power cable, telephone and other communication lines, and other equipment or peripherals exchange of communication line, at least two wires, conductors as line transmission of electricity or signal. But in addition to the two wires are usually there is a third conductor, this is the "ground". Interference voltage and current are divided into two kinds: one is two wires respectively for the transmission to and from the line; the other is a two wire do Avenue, ground do return to the road transport. The former is called the differential mode ", which is called" common-mode ".



What is the common mode rejection of residual pressure what is residual voltage

Common mode voltage (commonmodevoltage): in each of the conductor and the reference point (often dramatically or rack) of the average of the Phasor voltage. Or at the end of the two measurements and meter provides public between that part of the input voltage.

Differential mode voltage (symmetricalvoltage): a set of provisions of the conductor in any voltage between the two roots. The differential mode voltage also known as symmetric voltage.


On a specified waveform, nominal discharge current of the impulse valve plate, zinc-oxide Varistors ends the peak voltage measurement, known as the residual voltage. Residual voltage and pressure-sensitive voltage ratio, residual compression ratio. Lightning, lightning will input/output power lines generate instantaneous high voltage, high current, affect the user equipment and stable operation, would create serious damage to the equipment. Arrester press connection points can be divided into common-mode connection and differential-mode connection in two ways: arrester received in the line or the line between the zero line is called the differential mode Add method, the so-called lateral protection. Surge arresters connected between phase lines and ground wire or zero line and ground connection between called common mode, the so-called vertical protection.

Common mode interference in the signal lines and ground transport between, belongs to the asymmetry of interference. Eliminate common mode interference in several ways, including:
(1) adopt STP and effective grounding
(2) where strong electric should also consider using galvanized pipe shielding
(3) wiring away from high-voltage and high voltage power supply will power and signal cables together alignment
(4) do not and electronic lock with the same power
(5) assume linear regulated power supply or high-quality switching power supply (ripple noise less than 50mV