What are the various characteristics of the inductive device of the digital bridge? What are the principles?

Digital bridges are instruments that can measure inductance, capacitance, resistance, and impedance. This is a traditional habit. The earliest impedance measurement uses the true bridge method. With the development of modern analog and digital technologies, it has already been eliminated. This measurement method, but the name of the LCR bridge has been used ever since. If it is a LCR bridge using a microprocessor, it is called an LCR digital bridge. The general users also call these: LCR tester, LCR bridge, LCR meter, LCR Meter and so on.

Digital bridge principle

history

Digital bridge (volume name: electrician)

Digital bridge

A bridge that measures impedance parameters using digital techniques. Digital technology is the conversion of traditional analog quantities into digital quantities, followed by digital operations, transmission and processing.

In 1972, the world's first digital capacitive bridge with microprocessors, which combined analog circuits, digital circuits and computer technology, opened up a new path for impedance measuring instruments.

principle

The measurement object of the digital bridge is the parameters of the impedance component, including the AC resistance R, the inductance L and its quality factor Q, the capacitance C and its dissipation factor D. Therefore, the digital bridge is often referred to as a digital LCR meter. The measurement frequency is from the power frequency to about 100 kHz. The basic measurement error is 0.02%, which is generally around 0.1%.

Balanced bridge test principle

Balanced bridge test principle

Zx = Ux/Ix = Rr * Ux/Ur

This formula is a phasor relationship. If a phase sensitive detector (PSD) is used to measure the in-phase component and the quadrature component of Ux and Ur corresponding to a reference phasor, respectively, and then convert it into a digital quantity by an analog-to-digital conversion (A/D), and then The complex value and the reactance value of the measured impedance Zx can be obtained by a computer performing a complex operation.

It can be seen from the circuit and working principle in the figure that the digital bridge only inherits the traditional name of the bridge. In fact, it has lost the form of the traditional classic AC bridge, but at a higher level back to Ohm's law-based ammeter, voltmeter circuit and principle.

The digital bridge can be used for the verification and transmission of impedance gauges by the metrology test department, as well as the conventional measurement of impedance components in the general sector. Many digital bridges have a standard interface, which can automatically divide the measured components according to the accuracy of the measured value. It can also be directly connected to the automatic test system for automatic inspection of the product on the component production line to realize the production process. QC. In the mid-1980s, there were dozens of digital bridges with a common error of less than 0.1%. Digital bridges are evolving with greater accuracy, more functionality, speed, integration, and intelligence.

Wide range of measurement objects

Semiconductor components: Impedance parameter measurements of capacitors, inductors, magnetic cores, resistors, transformers, chip components, and network components.

Other components: impedance evaluation of printed circuit boards, relays, switches, cables, batteries, etc.

Dielectric materials: Loss angle evaluation of the dielectric constant of plastics, ceramics and other materials.

Magnetic Materials: Assessment of magnetic permeability and loss angle of ferrite, amorphous and other magnetic materials.

Semiconductor materials: dielectric constant, conductivity and CV characteristics of semiconductor materials.

Liquid crystal material: CV characteristics such as a dielectric constant and a spring constant of a liquid crystal cell.

Multiple component and material property measurement capabilities

Multi-parameter mixed display function

Multi-parameter simultaneous display can meet the comprehensive observation and evaluation requirements of various distributed parameters of complex components without having to repeatedly switch measurement parameters.

The inductor L and its DC resistance DCR can simultaneously measure the display, significantly improving the efficiency of the inductor measurement.

Reveal the many characteristics of inductive devices

The internal/external DC offset, combined with various scan test functions, allows accurate analysis of the performance of magnetic and inductive devices.

Through the bias current superposition test function, it is possible to accurately measure the low current superposition performance of high frequency inductive devices, communication transformers, and filters. Using an external current stacking device, the bias current can be up to 40A for accurate analysis of high power, high current inductive devices.

Precise ceramic capacitance measurement

1kHz and 1MHz are the main test frequencies for ceramic materials and capacitors. Ceramic capacitors are characterized by low loss values, while the AC signal applied by their capacity and loss produces significant changes.

The instrument has broadband testing capability and provides good accuracy, six-bit resolution and automatic level control (ALC) to meet the reliable and accurate testing needs of ceramic materials and capacitors.

Measurement of capacitance characteristics of liquid crystal cells

Capacitance-voltage (C-Vac) characteristics are the main method for evaluating the performance of liquid crystal materials. A problem encountered by conventional instruments for measuring the C-Vac characteristics of liquid crystal cells is that the maximum test voltage is insufficient.

The extended measurement option provides programmable test signal levels of 1% resolution and up to 20Vms, enabling it to measure capacitance characteristics of liquid crystal materials under optimal conditions.

Measurement of semiconductor materials and components

When evaluating the MOS type semiconductor manufacturing process, parameters such as oxide layer capacitance and substrate impurity density are required, which can be derived from the measurement results of the C-Vdc characteristics.

The C-VDC characteristic measurement can be conveniently performed by providing a DC source combined with various scanning functions.

In order to test semiconductor devices on the wafer, extension cables and probes are required, and the instrument's 1m/2m/4m extension cable option minimizes cable extension errors.

The distributed capacitance of various diodes, transistors, and MOS tubes is also the test content of this instrument.

Instructions

Power up

First connect the power cable with the IEC end to the IEC socket on the left rear of the bridge, the other end to the appropriate power outlet, and move the boat switch on the left rear of the bridge, even if the bridge is energized. When powered up, the display, range, and function indicators light up. The bridge can be automatically placed in the inductor and capacitance measurement files, parallel equivalent and 1KHz frequency state. Under normal circumstances, the internal circuit can be stabilized after a few seconds of power-on, and measurement can be performed.

2. Access method of the tested component

(1) Generally, the components of the radial lead can be directly inserted into the combined test clamp, and the components of the special flexible lead should be connected by the clamp clutch, which is located directly under the test clamp.

(2) When accessing the axial lead components, in order to avoid twisting the leads, an axial adapter can be used. First, insert the two fittings into the two ends of the test clip, and then adjust the spacing to the position suitable for the component measurement, and then The axial lead elements are inserted into the accessory clips at both ends.

(3) Where the axial adapter must be fairly fixed, such as when measuring a large number of similar components, a support plate is required.

Install the support plate: first adjust the axial adapter to the appropriate position, then suspend the support plate over the axial adapter, let each axial adapter pass through the slot on the support plate, and place the support plate Align the fixing screws with the screw holes on the bridge panel and finally tighten the screws. Note: It is not easy to tighten the screws too tightly during installation.

Note: Although the bridge can protect the charging capacitor access test, it is better to measure the charging capacitor after discharging it with a suitable resistor.

3. Note the reading and measurement conditions during use

(1) The 6-bit display of the instrument may not all be valid. In some measurements, the untailed value of the measured data may be large. The jitter values ​​should be discarded and the stable value read.

(2) Generally, the automatic range measurement is used to ensure that the correct range is selected, and the actual working range can be observed by operating to the manual mode. When applied to the batch test of the same batch of the same measuring component, the range lock mode can be selected to work.

(3) string--parallel indication

Although the bridge has the selectivity to display the equivalent values ​​in series or in parallel, in the case of unfavorable Q values, it is impossible to obtain basic accuracy in either of the above two ways. When it is necessary to change a display mode in order to improve the basic accuracy, the bridge indicates the series connection by the subscript s, and the subscript p indicates the parallel connection.

(4) Frequency prompt

Capacitance of 200μF~2000μF, inductance of 200H~2000H, only the basic accuracy can be obtained when the measurement frequency is 100Hz. Similarly, 200pF~2nF capacitors and 200μH~2mH inductors can only obtain basic accuracy at 1KHz measurement frequency. Therefore, for the best test performance, the most suitable test frequency should be selected.

(5) Test level display

High-K ceramic capacitors or high-conductivity magnetic inductors are sensitive to the level of the test signal, and different test levels can produce different measurements. At the same time, the lower the test level, the worse the measurement stability.

4. Recommended measurement conditions reference table

Table measurement condition reference

Component name measurement frequency string - parallel

Capacitance <1μF 1KHz parallel

Capacitance ≥1μF (electroless capacitor) 100Hz parallel

Capacitance ≥1μF (electrolytic capacitor) 100Hz series (SER)

Inductance <1H 1KHz Series (SER)

Inductance ≥1H 100Hz series (SHR)

Resistance <10KΩ 100Hz series (SHR)

Resistance ≥10KΩ 100Hz parallel

When the bridge is capable of providing series and parallel equivalent component values ​​at both 100 Hz and 1 kHz frequencies, it is recommended that certain types and values ​​of components be measured in a certain way. This is done in order to obtain a structural form that is most suitable for the component and that is most suitable for the measurement of the working mode commonly used by the component. For example, a large-capacity electrolytic capacitor, often used as a power filter element, will find that the capacitance at 1KHZ frequency is significantly lower than the capacitance at 100Hz. This phenomenon is due to factors related to the geometry of such components. Therefore, the capacitance value measured by the electrolytic capacitor at a frequency of 100 Hz is most useful. The loss term of the electrolytic capacitor is usually displayed on the series equivalent resistance (ESR), so the series capacitance and series resistance value should be measured.

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