CN201378188Y - Digitally controlled resistance measuring device - Google Patents

Abstract

The utility model discloses a numerically controlled resistance measuring device, which is characterized in that it comprises a microprocessor, an amplifier for amplifying the measured voltage, an AD converter, a DA converter, and a numerically controlled constant current for the measured resistance. flow source; the two input ends of the amplifier are connected to the two ends of the measured resistance; the output of the amplifier is connected to the microprocessor through the AD converter; the microprocessor is connected with the DA converter through the DA converter The input end of the digital control constant current source is connected, and the output end of the digital control constant current source is connected to the measured resistance, which is used to provide a constant current to the measured electronics. The device can independently, accurately and conveniently measure milliohm-level resistance, and has the characteristics of simple circuit design, perfect function, accurate measurement, low cost and the like.

Description

Digitally controlled resistance measuring device

technical field

The utility model belongs to the technical field of instruments and electronics, and relates to a numerically controlled resistance measuring device, which is especially suitable for measuring milliohm level resistance.

Background technique

In the analysis and design of the circuit, people often ignore the switch resistance, transformer or motor coil, and the resistance value of the wire in the PCB board, that is, they think that their resistance value is zero. Of course, in most cases, this analysis and design will not affect system design. However, when the operating current of the circuit or system is large, such analysis often brings large errors, and even causes the system to fail to work normally. During the analysis, it is found that it is precisely because of the existence of these milliohm-level resistors that we have ignored. The above-mentioned error and malfunction of the circuit. Therefore, in engineering design, especially in the practice of circuit measurement, it is often necessary to measure the small resistance values of switches, transformers or motor coils, and wires in PCB boards, so as to facilitate circuit design and analysis. At present, the special milliohmmeters on the market are relatively expensive, and ordinary multimeters are often not accurate enough.

Utility model content

The technical problem to be solved by the utility model is to provide a numerically controlled resistance measuring device, which can independently, accurately and conveniently measure milliohm level resistance.

The technical scheme of the utility model is as follows:

A numerically controlled resistance measuring device is characterized in that it includes a microprocessor, an amplifier for amplifying the measured voltage, an AD converter, a DA converter, and a numerically controlled constant current source that provides a constant current for the measured resistance; The two input terminals of the amplifier are connected to the two ends of the measured resistance; the output terminals of the amplifier are connected to the microprocessor through the AD converter; the microprocessor is connected to the numerical control constant through the DA converter The input end of the current source is connected, and the output end of the digitally controlled constant current source is connected to the measured resistance for providing constant current to the measured electrons.

Described microprocessor is single-chip microcomputer or DSP.

Advantage and effect of the present utility model:

The utility model adopts the most basic volt-ampere test method. The numerical control constant current source is composed of a digital-to-analog conversion circuit, an operational amplifier circuit and a voltage-controlled constant current source circuit. The voltage is collected by an operational amplifier circuit and an analog-to-digital conversion circuit. Data processing and display. The utility model provides a high-performance and practical milliohm meter circuit design scheme. The designed milliohm meter (that is, the device) has the characteristics of simple circuit design, perfect function, accurate measurement, and low cost.

Description of drawings

The structural block diagram of Fig. 1 utility model embodiment 1;

Fig. 2 is a schematic circuit diagram of a digitally controlled constant current source in Embodiment 1 of the utility model. (RL in the figure is the measured resistance. The input signal Vin is 0~4V)

Detailed ways

Example 1:

As shown in Figures 1 and 2, a numerically controlled resistance measuring device is characterized in that it includes a microprocessor, an amplifier for amplifying the measured voltage, an AD converter, a DA converter, and provides a constant current for the measured resistance The numerically controlled constant current source; The two input terminals of the amplifier are connected to the two ends of the measured resistance; the output terminals of the amplifier are connected to the microprocessor through the AD converter; the microprocessor passes the DA The converter is connected with the input end of the digital control constant current source, and the output end of the digital control constant current source is connected with the resistance under test for providing constant current to the electron under test. Described microprocessor is single-chip microcomputer.

This program adopts the most basic volt-ampere characteristic test method: pass a constant DC current through the measured resistance, obtain the voltage on the resistance through the measuring device, and calculate the resistance value of the measured resistance through the single-chip microcomputer. According to Ohm's theorem U=R×I, it can be seen that since the resistance is milliohm, if the current is milliampere, the resulting voltage value will be very small and difficult to identify through the ADC chip. Of course, a large current method can be used to collect larger However, if a large current is used, many small resistors cannot withstand a large current, or when the current is large, the heat generated is too large, which will cause damage to the circuit system. Therefore, the collected voltage signal is amplified, the tiny voltage signal is amplified, converted by AD, sent to the single-chip microcomputer, and the resistance value is calculated and displayed by the single-chip microcomputer. The block diagram of the overall scheme design of the system is shown in Figure 1.

Design of Numerical Control Constant Current Source Circuit

A digitally controlled constant current source provides constant current for resistance measurements. In this system, the single-chip microcomputer provides the size of the output constant current according to the resistance range of the measured resistance. The triode used in the actual circuit is TIP41. The triode itself does not have the function of controlling the current, but it plays the role of driving and expanding the current. U2B is a voltage follower and forms a negative feedback circuit with transistor Q2. The voltage on R9 is the input voltage Vin. The input voltage is equal to the voltage on R9, so the load RL current is I=U/R9.

Voltage amplification module and data processing module

After the measured DC voltage signal needs to be amplified 100 times, it can be transmitted to the AD chip and then processed by the single-chip microcomputer. The voltage amplification module is shown in Figure 2: the voltage amplification factor can be changed by adjusting the ratio of R2 to R1.

A single operational amplifier can be used to amplify one hundred times, or a cascade of two operational amplifiers can be used, each amplified by ten times. In the actual circuit production process, the above two methods are tested, and it is found that the effect of a single operation magnification of 100 times is relatively better. Therefore, in this design, a method of amplifying a single operation by 100 times is adopted.

After the voltage signal obtained by resistance measurement is amplified 100 times, it is transmitted to the ADC conversion chip through AD-IN. Calculated by the single-chip computer, the resistance value of the resistance can be obtained by dividing the obtained voltage by the constant current during measurement, but the resistance value at this time is not the actual resistance value measured, because the voltage is magnified one hundred times earned. Therefore, the result should be reduced by 100 times to get the real resistance value of the resistor.

The DAC5615 chip is controlled by the microcontroller to generate voltages of 40mV, 400mV, and 4000mV respectively, and the currents to be measured are 1mA (40mV/40Ω), 10mA (400mV/40Ω), and 100mA (4000mV/40Ω). In the actual circuit, it is only necessary to select the corresponding resistance measurement range, and the single-chip microcomputer controls the voltage-controlled current source circuit to output the required current.

Claims (2)

1. a digital control type electric resistance measuring apparatus is characterized in that, comprises microprocessor, is used for providing with the amplifier of tested voltage amplification, AD converter, DA converter, for measured resistance the digital-control constant-flow source of steady current; The two ends of two input termination measured resistance of described amplifier; The output terminal of described amplifier connects microprocessor through described AD converter; Described microprocessor is connected the output termination measured resistance of described digital-control constant-flow source by the DA converter with the input end of described digital-control constant-flow source.

2. digital control type electric resistance measuring apparatus according to claim 1 is characterized in that, described microprocessor is single-chip microcomputer or DSP.