In the rapidly developing world of electronics, precise measurements play a crucial role. Whether in the development of new devices, quality control in production or the calibration of measuring instruments – the accuracy of the measurement of electrical quantities is of fundamental importance. This is where measuring bridges come into play, which have become an indispensable tool in electronic measurement technology since their invention in the 19th century.
Measuring bridges make it possible to determine electrical quantities such as resistance, capacitance or inductance with the utmost precision. Their basic principle is based on the comparison of an unknown quantity with a known reference quantity. This comparison approach allows even the smallest deviations and differences to be recorded, making measuring bridges an essential instrument in modern electronics.
In converter technology, where the exact conversion of electrical signals is essential, measuring bridges are of particular relevance. They enable the precise characterization and calibration of transducers, which is essential for their reliability and accuracy. From the development of highly sensitive sensors to quality assurance in the mass production of electronic components – measuring bridges form the backbone of numerous measuring and testing processes.
The continuous development of measuring bridge technology, in particular the transition to digital systems, has further expanded their range of applications and further increased their precision. Today, measuring bridges are not only indispensable in laboratories and research facilities, but can be found in almost all areas of electronic measurement and control technology.
Basics of measuring bridge technology
The principle of the Wheatstone bridge
The Wheatstone bridge, named after the British physicist Charles Wheatstone, is the most basic and best-known form of measuring bridge. Its principle forms the basis for many other types of measuring bridge.
Wheatstone’s bridge consists of four resistors arranged in a square. Two adjacent corners of the square are connected to a voltage source, while a sensitive zero detector (usually a galvanometer) is connected between the other two corners.
The operating principle is based on the equilibrium state: if the ratio of the resistances on both sides of the bridge is the same, no current flows through the zero detector. This state is referred to as a “balanced bridge”. By varying a known resistance, an unknown resistance can be precisely determined by bringing the bridge into equilibrium.
The high accuracy of the Wheatstone bridge results from the fact that it performs a differential measurement, thus eliminating many systematic errors.
Types of measuring bridges in electronics
Based on the Wheatstone bridge, various specialized types of measuring bridges have been developed that are optimized for specific measuring tasks:
AC bridges
- Wien bridge: For measuring frequency and capacitance
- Maxwell bridge: For inductance measurements
- Schering bridge: For measuring capacitance and dissipation factor
Direct current bridges
- Kelvin double bridge: For very small resistances
- Thomson bridge: Also for precision measurements of small resistances
Autobalance bridges
These modern, often digital bridges balance themselves automatically and enable fast, precise measurements over a wide range.
Capacitance bridges
Specially developed for the precise measurement of capacitance, often with compensation for parasitic effects.
Inductance measuring bridges
Optimized for measuring inductance, often with options for measuring the quality factor.
Universal measuring bridges
Versatile devices that can record different measured variables by switching.
Each of these bridge types has its specific advantages and disadvantages and is selected according to the measurement task, required accuracy and quantity to be measured. The variety of available measuring bridges makes it possible to find an optimum solution for almost any measuring task in electronics.
The continuous development of measuring bridge technology, in particular the introduction of digital technologies, has further improved the accuracy, speed and user-friendliness of these instruments and constantly expanded their range of applications in modern electronics.
Measuring bridges in transformer technology
Application in current and voltage transformers
Measuring bridges play a central role in the development, calibration and testing of current and voltage transformers. These transformers are essential components in electrical systems that convert high currents or voltages into measurable quantities.
For current transformers
– Measuring bridges are used to check the accuracy of the transformation ratio.
– They enable precise measurement of the magnetizing current and the losses in the core.
– By using measuring bridges, phase errors and amplitude errors can be precisely determined.
For voltage transformers
– Measuring bridges are used to precisely determine the transformation ratio.
– They are used to measure the stray capacitances and inductances.
– The insulation properties are often checked using special capacitance measuring bridges.
The use of measuring bridges in this area enables high measurement accuracy, which is essential for the reliability and efficiency of energy transmission systems.
Use in sensor and measurement technology
Measuring bridges offer numerous advantages in sensor and measurement technology and are widely used:
Strain gages (DMS)
- Measuring bridges, in particular the Wheatstone bridge, are the basis for strain gauge-based force and pressure sensors.
- They enable the smallest mechanical deformations to be converted into measurable electrical signals.
- The bridge circuit compensates for temperature influences and increases sensitivity.
Temperature measurement
- Measuring bridges are used in conjunction with thermistors or resistance thermometers for precise temperature measurement.
- The bridge circuit allows a high resolution and linearization of the measured values.
Capacitive sensors
- Capacitive sensors in bridge circuits are often used to measure distance, level or humidity.
- The measuring bridge makes it possible to convert the smallest changes in capacitance into easily measurable voltage signals.
Inductive sensors
Inductive sensors are used for position or speed measurement and their signals are often evaluated with inductance measuring bridges.
Load cells
In precision weighing technology, measuring bridges with strain gages form the basis for high-precision measurements.
Advantages of measuring bridges in sensor technology
- High sensitivity: Measuring bridges can detect the smallest changes in the measured variable.
- Noise suppression: Differential measurement effectively suppresses interference signals.
- Temperature compensation: Many bridge circuits offer inherent temperature compensation.
- Linearization: With certain sensors, measuring bridges contribute to the linearization of the output signals.
- Versatility: Measuring bridges can be adapted to different sensor types and measuring tasks.
The use of measuring bridges in transducer technology, sensor technology and measurement technology therefore enables precise, reliable and low-interference measurements in a wide range of applications. From industrial process control to research and development, they form the basis for accurate and reproducible measurement results.
Precision measurements with modern measuring bridges
High-precision resistance measurements
Modern measuring bridges enable resistance measurements with extraordinary precision, which are essential for many applications in research and industry.
High performance
- Measurement accuracies of up to a few parts per billion (ppb) can be achieved with special bridges.
- Measuring range from microohms to several gigaohms, covering an enormous spectrum of resistance values.
- Resolutions in the nanoohm range for low-resistance measurements.
Techniques
- Use of direct current comparator bridges for maximum precision.
- Use of the four-wire measurement method to eliminate lead and contact resistances.
- Thermoelectric voltage compensation to reduce measurement errors due to thermal voltages.
Applications
- Calibration of precision resistors and standard resistors.
- Characterization of superconductors and semiconductors.
- Quality control in the electronics industry.
Capacitance and inductance measurements
Modern measuring bridges also offer outstanding performance in the measurement of capacitance and inductance, which is crucial for the development and testing of electronic components.
Capacitance measurements
- Accuracies in the range of 0.01% or better are achievable.
- Measuring range from femtofarads to several farads.
- Possibility of simultaneous dissipation factor measurement (tan δ).
Techniques
- Use of autobalance bridges for fast and precise measurements.
- Frequency variation to characterize frequency dependence.
- Compensation of parasitic capacitances by special circuit techniques.
Inductance measurements
- Accuracies of up to 0.05% with modern bridges.
- Measuring range from nanohenry to several henry.
- Simultaneous determination of the quality factor (Q).
Techniques
- Use of Maxwell or Hay bridges for precise inductance measurements.
- Use of multi-frequency measurement techniques for comprehensive characterization.
- Compensation of stray capacitances and inductances.
Common aspects
- Automatic calibration and zeroing to increase measurement accuracy.
- Digital signal processing for noise suppression and improved resolution.
- Ability to perform sweep measurements over frequency or voltage ranges.
Applications
- Characterization of passive components such as capacitors and coils.
- Development and quality control in the electronics industry.
- Materials research, particularly in the investigation of dielectric and magnetic properties.
The performance of modern measuring bridges in precision measurements makes it possible to detect even the smallest deviations and differences in electrical properties. This forms the basis for progress in many areas of electronics, from basic research to the development of high-precision electronic devices and systems. The continuous improvement of measuring bridge technology contributes significantly to increasing the quality and reliability of electronic components and systems.
Measuring bridges in quality assurance and calibration
Measuring bridges play an indispensable role in the quality assurance and calibration of modern electronic systems. Their precision and reliability make them a cornerstone in the metrological infrastructure, which is essential for the accuracy and comparability of measurements in industry and research.
Role in the calibration of measuring instruments
Measuring bridges serve as highly accurate reference instruments in the calibration of a wide range of measuring devices. Their ability to measure electrical quantities such as resistance, capacitance and inductance with exceptional accuracy makes them the ideal starting point for checking and adjusting other instruments. From simple multimeters to complex analyzers, measuring bridges often form the foundation of the calibration process.
The versatility of modern measuring bridges makes it possible to calibrate a wide range of measuring devices. In the electronics industry, for example, they are used to check LCR meters, which are essential for the quality control of components. In calibration laboratories, they are used to characterize precision resistors and capacitance standards, which in turn are used as references for other calibrations.
Due to their multifunctionality, measuring bridges contribute to efficiency and cost-effectiveness in quality assurance. Their ability to accurately measure multiple electrical quantities with a single device reduces the need for various specialized calibration tools. This not only simplifies calibration procedures, but also reduces the cost of maintaining metrological infrastructure.
Contribution to the traceability of measurements
A particularly important aspect of measuring bridges in quality assurance is their contribution to the traceability of measurements. Traceability means that every measurement can be traced back to international standards through an uninterrupted chain of comparisons. Measuring bridges often play a central role in this chain, as they can act as transfer standards between national metrological institutes and industrial calibration laboratories due to their high precision and stability.
The traceability supported by measurement bridges is of crucial importance for the global comparability of measurements. It enables companies to prove the quality of their products worldwide and meet regulatory requirements. In research, it ensures that results from different laboratories can be compared and reproduced – a cornerstone of scientific progress.
Conclusion: The indispensable role of measuring bridges in electronics
Since their invention in the 19th century, measuring bridges have become an indispensable tool in modern electronics. Their importance extends across various areas and applications, from basic research to industrial production. The central role of measuring bridges is summarized below, with a particular focus on their importance for precise transducer measurements.
In summary, it can be said that measuring bridges are far more than just one measuring instrument among many. They are a fundamental building block of modern electronics, enabling precision, reliability and innovation. Their central importance for precise transducer measurements and beyond makes them an indispensable tool in a world that is increasingly characterized by electronic systems. As such, measuring bridges will remain a mainstay in the development and quality assurance of electronic technologies in the future.