The principle of making a detector for instantaneous current change

The transient current detector circuit principle uses TL084 junction field effect tube input operational amplifier. Each operational amplifier uses high voltage junction field effect tube and bipolar tube on a single integrated circuit, which is compatible with better matching, high conversion rate, small input base current and input drift current, and low drift voltage temperature coefficient. Integrated operational amplifier A and R1 form a short-circuit current amplifier, B and R2~R6, W1 form an inverting adder, which amplifies the output voltage V1 of operational amplifier A. Among them, R3, R4 and W1 form a circuit. If the output voltage VO of operational amplifier B is VO≠0 when the input i=0, the movable contact of the multi-turn potentiometer W1 can be moved to make VO=0. In fact, W1 is equivalent to the role of the pointer type galvanometer zero adjustment knob. The voltage amplification factor of operational amplifier B is AV=-R6/R2=-40. R7~R17 series voltage divider generates 10 reference voltages, and each integrated operational amplifier is connected to a voltage comparator, and forms a level indication circuit with resistors and light-emitting diodes.
 The op amps A to M use three op amp integrated circuits TL084, each of which contains four identical operational amplifiers. They share a common power supply and work independently. The light-emitting diode LED6 is red or yellow, and the other LEDs of the safety test instrument are green. They all use φ6 high brightness. All resistors use 1/8 W metal film resistors with an accuracy of 1±%. C1 uses an electrolytic capacitor with a withstand voltage of 25 V, and W1 uses a multi-turn potentiometer with a resistance of 1 kΩ. The power supply uses a ±5 V dual-output regulated power supply. Except for the potentiometer W1, LED and current limiting resistors R18~R28, the remaining components are designed to be installed on a copper-clad board. The circuit board diagram is shown in Figure 3. All current limiting resistors are soldered together with the LED to reduce the number of leads. In order to adapt to the observation habits of pointer-type galvanometers, LED1~LED11 can be installed on the panel in a fan-shaped arrangement, and LED6 is arranged in the middle, as shown in Figure 3. In order to facilitate students' observation, the external dimensions of the current detector can be appropriately larger, such as: 40 cm high, 25 cm wide, and 10 cm thick. As long as the components are correct and installed correctly, they can work normally without debugging. The production principle of the detector for instantaneous current changes
 The detector for instantaneous current changes overcomes the inherent shortcomings of pointer-type and cursor-type galvanometers in the circuit, which have large losses and slow response speeds. It can detect instantaneous current changes and is suitable for detecting instantaneous currents that require small losses and small loop resistance in the circuit to be tested.
  With the characteristics of high conversion rate of integrated operational amplifier circuits, small input base current and drift current, and small drift voltage temperature coefficient, the principle of short-circuit current amplifier is used to amplify the current to be detected by 1:1, widen the required range of the internal resistance of the signal, improve the sensitivity of detection, and realize the detection of instantaneous current changes. The input signal Vi is connected to the inverting input terminal ∑ of the integrated operational amplifier through resistor R1, while the non-inverting input terminal ∑ is grounded through resistor R2. The dynamometer output voltage VO is connected back to the inverting input terminal through the feedback resistor RF, forming a deep voltage negative feedback. In practical applications, in order to ensure that the two input terminals of the operational amplifier are in a balanced working state and avoid the input bias current generating additional differential input voltage, the resistance of the inverting input terminal and the non-inverting input terminal to ground should be equal.