Abstract : Currently, there is a wide range of test and measurement hardware and software to choose from. This article systematically describes the various parameters and factors you need to consider when making a decision, introduces four types of test equipment structures and their advantages and disadvantages, and finally offers some suggestions for reference. Keywords : Spectrum Channel Choosing from the available test and measurement hardware and software is understandably difficult for both novice and experienced users. Technological advancements have accelerated the development of measurement and testing methods exponentially, providing users with unimaginably powerful system capabilities. Test and measurement equipment spans a wide range. For simple applications, it is relatively easy to choose a suitable structure to meet the needs and budget. As the complexity of the application increases, the choice of structure and related costs also become more complex, leading to incorrect choices and higher costs, making the correct choice even more important. The starting point is to know the level of the signal or sensor output and the sensitivity required for the measurement (defined as the smallest change that can be detected during measurement and expressed in units of measurement). Accuracy, resolution, and measurement speed are some important factors that engineers must consider when deciding how to collect and measure data. Another important factor is the environment. Is the measurement conducted in a noisy factory environment or a quiet laboratory? Additionally, is the sensor located too far away to be easily accessible? In many applications, environmental factors can play a decisive role in the structural design. Measurement Requirements : 1. Sensitivity: The smallest detectable change in the measured signal; 2. Accuracy: The degree of agreement between the measured value and a primary standard; 3. Resolution: The smallest portion of the observed signal; 4. Measurement Speed: Maximum sampling rate; 5. Bandwidth: The highest frequency signal component of the sampled signal; 6. Data storage requirements; Number of channels to be measured; 7. Number of I/Os: Analog and digital; 8. Triggering: Timing control and switching control; 9. Noise immunity: Normal noise rejection ratio and its analog rejection ratio; 10. Signal conditioning; Isolation; 11. Network/bus protocol requirements, such as Ethernet and IEEE-488 (GPIB); 12. Display; Ease of setup and use; 13. Calculation and analysis of collected data; 14. Size, weight, and portability; 15. Power requirements; System integration issues; 16. System cost and cost per channel. After considering these factors and specifying your requirements, you can consider the correct system architecture for your application. Instrument Structure Selection There are four main types of test equipment structures: 1. Standalone Instruments. The most accurate and sensitive standalone instruments are benchtop instruments. These are traditional instruments with many new and improved features, such as graphical displays, key selection functions, and menu programming. Portable digital multimeters with self-powered power supplies are used for field measurements, but generally, they do not have the performance, sensitivity, and accuracy of benchtop instruments. 2. Computer-Connected Instruments. This is a subset of standalone instruments. These are used when the quantity or type of measurements exceeds the capacity of a standalone instrument, requiring a terminal display or flexible software control. Many instruments offer both standalone operation and computer control modes for complex measurement methods and systems. The external data communication bus connecting the instrument to the PC controller can use one of several standard protocols. 3. Distributed Instruments. Currently provided by some manufacturers. This type of test system consists of several standalone instruments connected together via a communication network. This structure consists of miniaturized instruments and can, in principle, be placed anywhere in the factory, transmitting fully processed signals to the computer via the communication network. Many instruments meet laboratory-grade measurement requirements. Because they are located near the test signals, cable-induced noise is minimized, thus reducing measurement errors. The biggest advantage of a distributed instrument network layout is the elimination of cable connections from each test point to the PC, simplifying installation. A small local monitor can be placed near the instrument to read data and troubleshoot. You can also rely entirely on the monitor on the control computer. Distributed instruments use data communication protocols similar to those used by computer-connected instruments. 4. PC-based test instruments. The most important attributes here are measurement speed and the ability to acquire large amounts of data. There are two basic configurations. The most common is that analog test signals are connected to a PC plug-in board located on a computer bus slot or on a PC parallel port. Another configuration consists of many boards mounted in a chassis, which is rack-mounted and positioned a considerable distance from the PC. The chassis contains measurement boards, multiplexing boards, A/D conversion boards, and signal conditioning boards, which network the fully processed digital signals with the PC. The chassis system effectively expands the scale of the measurement system, offering a much larger number of channels than using a PC with only a few available board slots. Checking Parameters An important parameter determining the sensitivity of a digitizing instrument is resolution and sensitivity, where sensitivity equals the range divided by the resolution. Therefore, for a given instrument's measurement range, higher resolution results in better sensitivity. Sampling rate (or measurement speed) is another parameter, but this comes at the cost of sensitivity. The desired instrument accuracy (how close the measured value is to a primary standard) must also be considered. Accuracy is expressed in several ways, depending on the specific instrument. However, it is typically expressed as a percentage, PPM, or bits. Benchtop stand-alone instruments offer the highest accuracy, sensitivity, and resolution. They are suitable as calibration sources for transferring standards. For each basic type of instrument, some of the parameters discussed above, along with others, are listed in Table 1. Adaptability and Noise Suppression Various additional signal conditioning amplifiers can be used to boost signal levels input to PC-based test systems, allowing this type of system to operate with low-level signals (e.g., signals from low-voltage couplers, strain gauges, etc.). Deciding on the type of hardware often involves trade-offs between various required properties. Table 1 Typical Structural Properties Measurement Parameters Standalone Instruments Distributed Instruments PC-Based Test Instruments Sensitivity 1nV 100nV 5μV Resolution 20 to 28 bits 16 to 20 bits 12 to 16 bits Sampling Rate 2KSampIe/s 30kSampIe/s 330KSampIe/s Number of Channels 1 8 or more Some 8 or 16 Switching Speed ​​Medium Limited Height Form Factor Benchtop/Rack, Push-to-Place/Portable Miniaturized/Remote Determined by PC Software Function Convenient/No Setup Required/Required for Communication[/align] These specifications reflect the highest or optimal values ​​that each parameter of this type of instrument can typically achieve, and not all of these values ​​simultaneously. Some measuring instruments have built-in noise suppression devices. They use internal techniques such as filtering, integration, and current inversion to reduce noise. However, there are no built-in noise suppression devices in PC-based insertion loss and PC-based external chassis systems. An alternative approach is to use software-provided averaging techniques in PC-based test systems to reduce noise from measurement and/or signal conditioning add-ons such as filters. In short, a drawback of PCs is their inherently noisy bus, which limits the use of PC plug-in boards for sensitive measurements. Conclusion Finally, cost is a consideration. Benchtop instruments are the most expensive, and therefore should only be used when there is a genuine need for accuracy and resolution. Since almost everyone owns a PC, PC-based systems are likely the best solution in terms of cost and flexibility. If measurements are required in environments with high electrical noise, distributed miniaturized instruments will be your best option. The price of these instruments falls between that of benchtop and PC plug-in instruments.