KSD211B 3BHE022455R1101 ABB 输入耦合单元ICU

KSD211B101 3BHE022455R1101

For example, the following full wave rectifier circuit, where the transformer transformer transformer ratio of 10:1 (output voltage output than the input voltage is 10 times smaller), channel A is to detect the AC voltage signal before rectification (in order to distinguish from other wires, changed to yellow), channel B detects the voltage signal after rectification. The two diode models are 1N4148 with a load resistance of 40 ohms.

In order to facilitate observation, the A channel signal waveform diagram is moved down 1.4 grids.

In Figure A and B channel signal coupling input mode, when DC coupling is selected, the waveform of B channel is in line with the theoretical unidirectional pulse characteristics after full wave rectification, and the frequency is twice that of the signal frequency before rectification.

When the input mode of B channel signal coupling is changed to AC coupling, the waveform of B channel moves down a distance. See the following figure:

Why does this happen? What happens to the input signal because of the AC coupling input. What is DC coupling and AC coupling? And what about the middle 0 coupling?

In the field of signal processing, this is a debatable topic. What is AC coupling and DC coupling? Let’s start with what coupling is.

What is coupling?

The transmission process (or mode of transmission) of energy from one medium to another is called coupling. For example, the transmission process of electric energy from metal wires to optical cables is a coupling, the kinetic energy of the motor becomes the pressure energy of the hydraulic pump, and the intermediate transmission process is also a coupling. Coupling can be understood as a means of transmission, or transformation.

The oscilloscope in the above circuit converts the electrical signal at the input end of the channel into the electrical signal displayed on the screen through AC coupling or DC coupling. What kind of transformation is AC and DC coupling?

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First, DC coupling can allow AC and DC signals in the circuit to pass at the same time, or it can be understood that it does not intercept the signal and allows all types of signals to pass. Therefore, DC coupling can show the original appearance of a signal, but in circuit analysis, what is often needed is a useful signal in a signal source, such as a signal

V (t) = Vsin + 5 + phi (wt)

This signal source contains an AC signal

V (t) = Vsin + phi (wt)

And a DC signal 5 volts. A signal source like this is generally referred to as an AC signal with a 5 volt DC bias.

If we only need the signal that is useful for circuit analysis, such as the AC signal, then the signal source can be coupled through AC.

AC coupling allows only AC signals to pass through. When the oscilloscope selects the AC coupled input mode, it is actually to add a capacitor to the input circuit, so as to isolate the DC signal, so that the oscilloscope screen only displays the AC component of the signal source, which is convenient for engineers to detect the circuit.

To put it bluntly, DC coupling is not to do any processing on the input signal, and does not have any impact on the input signal.

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