Lecture 1 on function analysis of the hottest freq

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Frequency converter function analysis lecture (I)

1 frequency setting mode and selection

1.1 basic concept

(1) basic meaning of setting mode

to adjust the output frequency of the frequency converter, you must first provide the frequency converter with a signal that changes the frequency. This signal is called the frequency setting signal, and it is also called the frequency command signal or the frequency reference signal. The so-called given mode is the specific method to adjust the output frequency of the frequency converter, that is, the way to provide a given signal

(2) panel setting mode

the mode of frequency setting (i.e. adjusting the frequency) through the keyboard or potentiometer on the panel is called panel setting mode. There are two cases of panel setting, as shown in Figure 1:

(a) the size of the given frequency of the keyboard is given through the up key (▲) and down key (Q key) on the keyboard. Keyboard setting belongs to numerical quantity setting, with high accuracy

(b) the potentiometer is set on the panel for the given part of the frequency converter, as shown in Figure 1 (a). The frequency can also be adjusted by potentiometer. Potentiometer setting belongs to analog quantity setting, and the accuracy is slightly low

panel setting mode of frequency in Figure 1

most frequency converters do not have potentiometers on the panel, so the "panel setting" mentioned in the manual is actually keyboard setting

the panel of the frequency converter can usually be removed and placed in a convenient place for users to operate through an extension cable, as shown in Figure 2

Figure 2 panel remote control setting

in addition, which setting method to adopt must be decided in advance through function preset

(3) external setting mode

input the frequency setting signal from the external input terminal to adjust the output frequency of the frequency converter, which is called external setting or remote control setting. The main external setting methods are:

(a) external analog setting

input analog signal (voltage or current) from the outside of the frequency converter through the external setting terminal, and adjust the output frequency of the frequency converter by adjusting the size of the given signal

the types of analog quantity given signals are:

· voltage signal

take the voltage as the given signal. The range of given signal includes: 0~10v, 2~10v, 0~ ± 10V, 0~5v, 1~5v, 0~ ± 5V, etc

Larsen believes that the current signal

takes the current as the given signal. 1 - pressing depth under the initial experimental force F0; The range of given signal is: 0~20ma, 4~20ma, etc

(b) external digital quantity setting

is given by inputting the switch signal through the external switch quantity terminal

(c) external pulse setting

it is given by inputting pulse sequence through external terminal

(d) communication setting

frequency setting is carried out by PLC or computer through communication interface

1.2 general principles for selecting a given method

(1) panel setting and external setting

panel setting is preferred. Because the operation panel of the frequency converter includes keyboard and display screen, and the display function of the display screen is very complete. For example, various parameters and fault codes during operation can be displayed

however, due to the limitation of the length of the connecting wire, the distance between the control panel and the frequency converter cannot be too long

(2) digital quantity setting and analog quantity setting

digital quantity setting is preferred. Because:

(a) the timing frequency accuracy of digital quantity is high

(b) digital quantity setting is operated through common contacts, which is not only not easy to be damaged, but also has strong anti-interference ability

(3) voltage signal and current signal

current signal is preferred. Because the current signal is not affected by the line voltage drop, contact resistance and its voltage drop, stray thermoelectric effect and induced noise in the transmission process, it has strong anti-interference ability

however, due to the complexity of the current signal circuit, the voltage setting method is still used in the majority in the case of a short distance. 2 adjustment function of analog quantity setting

2.1 basic concept

(1) definition of frequency setting line

the frequency is given by analog quantity, and the given signal x of frequency converter (x is the general term of the given signal, which can be either voltage signal UG, or the relationship curve between current signal Ig and the corresponding given frequency FX, FX = f (x), is called frequency setting line

(2) basic frequency setting line

(a) definition

in the process of the given signal x increasing from 0 to the maximum value xmax, the frequency setting line of the given frequency FX linearly increasing from 0 to the maximum frequency Fmax is called the basic frequency setting line that people have only one youth in a lifetime. Its starting point is (x = 0, FX = 0); The end point is (x = xmax, FX = Fmax), as shown in Figure 3 (a) and (b)

Figure 3 basic frequency setting line

for example, the given signal is UG = 0 ~ 10V, and the corresponding output frequency is required to be FX = 0 ~ 50Hz

then: UG = 0V corresponds to FX = 0Hz; UG = 10V and FX, and make the adjacent coils closely arranged in a spiral coil = 50Hz corresponding

(2) the maximum frequency fmax

is the maximum frequency that the frequency converter is allowed to output when the digital quantity is given (including keyboard setting, external speed up/speed down setting, external multi gear speed setting, etc.); When the analog quantity is given, it is the frequency corresponding to the maximum given signal

(3) frequency setting

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