Measurement circuit of direct current

Abstract

The invention provides a measurement circuit of direct current, comprising a main circuit of the direct current to be measured. In the measurement circuit of direct current, a first conductor is connected with the main circuit in series; one end of a second conductor is connected with the first conductor; the resistance of the first conductor is less than that of the second conductor; the other end of the second conductor is respectively connected with a drain electrode of a first field effect transistor of the measurement circuit of direct current and a positive voltage input end of an operational amplifier; the other end of the first conductor is connected with a negative voltage input end of the operational amplifier of the measurement circuit of direct current; an output end of the operational amplifier is connected with a grid electrode of the first field effect transistor; a source electrode of the first field effect transistor is connected with one end of an amperemeter; and the other end of the amperemeter is connected with the ground of the measurement circuit of direct current. The invention can accurately detect high current, and has low power consumption and large scope of detected current.

Description

technical field [0001] The invention relates to the field of large current measurement, in particular to a direct current measurement circuit. Background technique [0002] DC current measurement has always been a problem to be solved for high power DC powered electrical equipment. By measuring the current, people can know the amount of power consumption, whether the electrical equipment has safety problems such as short circuit and overload, so as to take relevant protective measures to avoid accidents. If the device is powered by a battery, the measurement of the current is directly related to the calculation of the remaining battery capacity, which affects the operation of the device, the use and maintenance of the battery. Therefore, the measurement of DC current, especially the measurement of large current is very important. [0003] The traditional measurement circuit is relatively simple, and generally the shunt is directly connected in series to the main circuit. ...

AI Technical Summary

Problems solved by technology

[0004] However, using a shunt to measure current also has many disadvantages. First, the shunt is connected in series in the main circuit. It will generate heat due to the large current flowing through it, and consume a certain amount of power.

The above example illustrates that a 100A current produces a voltage drop of 75mV on the shunt, and consumes 7.5W of power. This power is emitted in the form of heat, which increases the temperature of the shunt and changes the resistance of the resistor. , causing measurement errors, and the heat-generating shunt may affect the surrounding instruments and equipment, and even cause accidents

Secondly, to measure the voltage of 75mV requires a very high-precision voltmeter, and the cost is high

At present, digital voltmeters are commonly used, and the input voltage is converted into a digital signal by analog-to-digital conversion and then processed. However, the accuracy of analog-to-digital conversion is limited, especially when the input is low, because of the limitation of quantization accuracy, the measurement error will be large. It is very large and is seriously affected by noise, so it is difficult to guarantee the accuracy of using a shunt to measure large currents

Third, the measurement range of the shunt is fixed and cannot be measured in stages, so the range of use is limited

[0005] In addition, the industry also uses the isolated current sensor based on the Hall element to measure the current. It is characterized by being isolated from the circuit of the measured current, and there is no disadvantage such as heat generation of the shunt, but this method has measurement linearity. Disadvantages such as poor temperature, large zero drift, poor thermal stability, etc.

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