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Common mode and differential mode

Time:2023-09-30 Views:672
What are common mode interference and differential mode interference
    When the changes in voltage and current are transmitted through wires, there are two forms, which we refer to as "common mode" and "differential mode". The power line of a device, communication line of a telephone, etc., and communication line exchanged with other devices or peripheral devices must have at least two wires, which serve as round-trip lines to transmit power or signals. But there is usually a third conductor outside these two wires, which is the "ground wire". There are two types of interference voltage and current: one is that two wires are used as round-trip transmission lines; The other method is to use two wires as the destination and the ground wire as the return path for transmission. The former is called "differential mode", while the latter is called "common mode". For differential amplifiers, if the two input interference signals are of unequal size or in different directions, they are considered differential mode interference signals.
    Usually, the electrical appliances we use are two wires, one live wire (L) and one neutral wire (N). The neutral wire is considered the neutral wire of three-phase electricity, and there is also a grounding wire called the ground wire,. The interference between the zero wire and the live wire is called differential mode interference, while the interference between the live wire and the ground wire is called common mode interference. It is considered that there is no voltage between the ground and the zero line, or it can be considered that the zero line has no voltage and cannot drive the electrical appliance. Therefore, it is considered that there is no interference between the zero line and the ground line.
What is common mode residual voltage and what is common mode residual voltage
    Common mode voltage: The average value of the phasor voltage that occurs between each conductor and a specified reference point (often ground or frame). Alternatively, the part of the input voltage that is simultaneously applied between the two measuring terminals of the voltmeter and the specified common terminal.
    Differential voltage: The voltage between any two charged conductors in a specified set. Differential mode voltage, also known as symmetrical voltage.
    In the specified waveform, the nominal discharge current impacts the zinc oxide valve plate, and the voltage peak measured at both ends of the valve plate is called residual voltage. The ratio of residual voltage to voltage sensitive voltage, residual voltage ratio. Lightning strikes can generate instantaneous high voltage and high current on input/output power lines, affecting the stable operation of user equipment, and in severe cases, causing equipment damage. Lightning arresters can be divided into two types according to their connection methods: common mode connection and differential mode connection. The connection of lightning arresters between phase lines or between phase lines and zero lines is called differential mode connection, which is also known as lateral protection. The connection of lightning arrester between phase line and ground line or between zero line and ground line is called common mode connection, which is called longitudinal protection.
Common mode signal
    Common Mode Signals
    A common mode signal is the same signal that acts on the same or opposite input end of a differential amplifier or instrument amplifier. For example, the noise voltage introduced into two balanced terminals in a balanced pair. Another example is the DC voltage applied to the balance line (such as the DC level generated by the ground potential difference between the signal source and receiver).
    For an ideal differential amplifier, the common mode signal output can be completely eliminated because the differential inputs (in phase and out phase) cancel out the same input components. The parameter that measures this characteristic is called the common mode rejection ratio or CMRR.
brief introduction
    Common mode voltage: The average value of the phasor voltage that occurs between each conductor and a specified reference point (often ground or frame). Alternatively, the part of the input voltage that is simultaneously applied between the two measuring terminals of the voltmeter and the specified common terminal.
form
    Common mode and differential mode are the two forms of voltage and current changes transmitted through wires.
    There are two types of interference voltage and current: one is that two wires are used as round-trip transmission lines; The other method is to use two wires as the destination and the ground wire as the return path for transmission. The former is called "differential mode" and the latter is called "common mode".
    Power line noise is caused by electromagnetic disturbances generated by various electrical equipment in the power grid that propagate along the power line. Power line noise is divided into two categories: common mode interference and differential mode interference. Common mode interference is defined as the unwanted potential difference between any current carrying conductor and the reference ground; Differential mode interference is defined as the unwanted potential difference between any two current carrying conductors.
    Any conducted interference signal on the power line can be represented by differential and common mode signals. Differential mode interference propagates between two wires and belongs to symmetric interference; Common mode interference is transmitted between the wire and the ground (casing), which belongs to asymmetric interference. In general, the amplitude of differential mode interference is small, the frequency is low, and the interference caused is relatively small; Common mode interference has a large amplitude and high frequency, and can also generate radiation through wires, resulting in significant interference.
    Common mode interference: Generally refers to noise generated on two signal lines with equal amplitude and phase.
What are common mode interference and differential mode interference
    When the changes in voltage and current are transmitted through wires, there are two forms, which we refer to as "common mode" and "differential mode". The power lines of equipment, communication lines of telephones, and communication lines exchanged with other equipment or peripheral devices have at least two wires, which are used as round-trip lines to transmit power or signals. However, there is usually a third conductor in addition to these two wires, This is the "ground wire". Interference voltage and current can be divided into two types: one is that two wires are used as round-trip transmission lines; The other method is to use two wires as the destination and the ground wire as the return path for transmission. The former is called "differential mode" and the latter is called "common mode"
    Common mode interference is transmitted between signal lines and ground, and belongs to asymmetric interference. The methods for eliminating common mode interference include:
    (1) Using shielded twisted pair and effectively grounded
    (2) Galvanised pipe shielding should also be considered in areas with strong electric fields
    (3) When wiring, stay away from high-voltage wires, and do not bundle high-voltage power and signal wires together for routing
    (4) Do not share the same power supply with the electronic lock
    (5) Using linear regulated power supply or high-quality switching power supply (ripple interference less than 50mV)
  




 












   
      
      
   
   


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