Device Introduction
There are some sensitive current type loads (such as generator excitation windings, electromagnetic actuators, etc.) in industrial production, and their common feature is to have strict dynamics for load currents. And steady state requirements, while satisfying the output current is smooth, the output current is required to quickly follow the current command. The current amplifier is based on current instructions to provide current to the sensing current load, essentially the controlled current source.
The current amplifier is generally composed of four parts of the power supply, power electronics, inductive load, controllers, and output current turning loop control, and the basic structure thereof is shown in FIG. Ideal Current Amplifier Requires Output Current i m (t) fully reproduced current command i ref (t), i.e., i m (t) = I ref (t). Since the sensitive load current cannot be mutated, the inductive load conveys the current as a inertial link. This inertia often causes the load current change in the current command change, which is unfavorable for the system for current response requirements. Increasing load inductance helps reduce current amplifier output current ripple, but at the same time, the inertia of the load is increased, and the dynamic response speed of the system is reduced.
It can be seen that the current steady state output quality and current response speed are a pair of contradictions. The most effective measure to solve this contradictory is to increase current response speed in the control system adopt appropriate compensation links.
amplifier
The amplifier is an apparatus for increasing signal amplitude or power, which is an important component of the process of processing signals in the automated technology tool. The amplification of the amplifier is to be implemented with the input signal control energy, and the enlarged power consumption is provided by energy. For linear amplifiers, the output is the reproduction and enhancement of the input signal. For nonlinear amplifiers, the output is a certain function relationship with the input signal. The amplifier is divided into mechanical amplifiers, electromechanical amplifiers, electronic amplifiers, hydraulic amplifiers, and pneumatic amplifiers according to the physical quantity of the signal processed, and the most widely used electron amplifier. With the promotion of jet technology, the application of liquid or pneumatic amplifiers has gradually increased. The electronic amplifier is divided into vacuum tube amplifiers, transistor amplifiers, solid amplifiers, and magnetic amplifiers in accordance with the active devices used. Among them, it is the most widely used in transistor amplifiers. In the automation meter, the transistor amplifier is often used for voltage amplification and current amplification, and the main form is single-ended amplification and push-pull enlargement. In addition, it is often used in impedance matching, isolation, current-voltage conversion, charge-voltage conversion (such as charge amplifier) and a certain function relationship between output and input using an amplifier (such as an arithmetic amplifier).
Structure and Principle
Circuit Structure
The current amplifier circuit topology can be a voltage, current in the first quadrant BUCK circuit, or a current unidirection The H bridge circuit of the flow, the voltage double reference can also be used, and the topological circuit structure is shown in Figs. 2 (a) to 2 (c). These three circuit structures are flexibly selected for different applications.
Basic principle
The current amplifier adopts output current closing loop control, and its control schematic is shown in Figure 3. As can be seen from Figure 3, the main factor affecting the speed of the current output response is the time constant T e = l / r L = L / R L , when this time constant is large. The output current response is difficult to improve. Therefore, the main measure to improve the response speed of the current amplifier is to reduce the equivalent time constant of the controlled object.
Examples
Ji Shili 428-PROG programmable current amplifier enables an enlarged low current. 428 Current amplifier Quick conversion small current is a voltage signal, and then use an oscilloscope, a waveform analyzer or a data acquisition system to display or measure.
Main features and advantages :
1,2μs rise time;
2, 1.2 Fa RMS noise;
3, gain up to 1011 V / A;
4, compatible with IEEE-488 interface / 5,428 adopts advanced "feedback current" circuit to achieve fast Rising time and noise below Pi'an. The gain of 428 is adjustable from 103V / A to 1011V / A, the step size is 10 times, and the rise time can be selected from 2 μs to 300 ms.
Application range :
Biochemical measurement: from the ion channel current of the cell wall and the cell membrane.
Beam Direction Monitoring: Used for electronic storage rings and synchronous accelerators.
Surface scientific research: The amplifier of the tunnel electron microscope system is scanned.
Observe the secondary electron emission (such as X-ray and electron beam current), laser and light measurement and PMT (photoelectric multiplier) and photodiode, fast optical conductive material Analysis, IR detection amplifier.