The multimeter is one of the most commonly used measuring instruments for electronic enthusiasts. It is an instrument that integrates many common electrical measurement functions. The common multimeter has three basic test items of voltage, current and resistance. Nowadays, many multimeters are developing in the direction of intelligence and multi-function, so many digital products have automatic range selection and extended functions such as measuring capacitance, inductance, frequency, duty cycle, temperature, and triode amplification. Generally, the low-end multimeter technology has become very popular, and some small workshops can produce a variety of multi-function digital multimeters, and the price is very low. The price of a multimeter in the market ranges from a few yuan to several thousand dollars. How do we choose a multimeter that meets the needs of our application?
The purchase of a multimeter should be considered from the aspects of product performance, brand, appearance, after-sales service, price and so on.
Performance of the multimeter The performance of the multimeter mainly includes five aspects: measurement accuracy, extended function, reliability, durability, and product safety characteristics.
The accuracy of the multimeter includes two aspects: one is the accuracy of the measurement, which is commonly referred to as the “error”; the other is the resolution of the measurement, which is commonly referred to as the “number of bits of the multimeter”. The measurement resolution of the multimeter is not necessarily related to the measurement accuracy. Although it is generally said that the measurement resolution is higher and the measurement accuracy is better, it is not absolutely true.
Some manufacturers are opportunistic, the product seems to display more digits, more functions, but limited by cost and technology, can not control the accuracy and stability, a three-and-a-half-digit multimeter measurement accuracy is better than one It seems entirely possible that the station looks like a product with four and a half displays. The resolution of the multimeter is based on accuracy, otherwise the display of high digits is not measured. In the high-demand measurement, the measurement accuracy of the multimeter is quite demanding, and the measurement accuracy of the multimeter is one of the main indicators for measuring the product grade.
The measurement accuracy of a multimeter will slowly degrade over time, which is the main reason why the instrument needs regular calibration. The high-reliability multimeter has a long service life and is resistant to harsh external environments. The cause of the multimeter error is inherent and external: the external cause is the use environment and the frequency of use. High and low temperature and high humidity will affect the characteristics of the components. As the number of times and time increases, wear and aging It is inevitable; the internal factors are the quality of the product, from circuit design to component selection and manufacturing processes. The same function of components, there are expensive but low temperature coefficient, excellent performance, durable products, but also low-cost but flat performance products, the use of components of the grade is directly related to the cost of the product, manufacturers of different brands are Different considerations.
Taking the high-end brand, the high-stability components and design are selected according to the principle of high quality and high price, ensuring the reliability and durability of the product. Although the price is higher, the product performance is stable, the service life is long, and the repair rate is low. The brand that takes the “price” route strictly controls the cost and even shrinks. Although such a product is cheap, it may not be easy to find the problem at the beginning of use, but as the use time is extended, the problem will be slowly exposed. Fortunately, most low-end users are not sensitive to the accuracy of the multimeter, and there is no means of measurement. Generally, the dry battery display shows 1.5xxV, and the measured power supply shows 22xV. So many users say that their cheap multimeter quality. Ok, it hasn’t been broken for many years. In fact, many products are really taken to measure, and they are no longer in the “state”.
The durability of the multimeter is closely related to the design and quality of the product. Durable products are designed with the multimeter in a tough environment, including wind and rain and accidental drops and collisions. High-strength housing materials and impact-resistant design and high sealing are the basis for increased product durability. Internal high-quality components can delay long-term wear and tear. Some high-quality multimeter dials are made of high-quality metal, and the contacts are made of thick gold plating, which can resist oxidation and wear. Some famous brand multimeters produced more than 10 years ago have been repeatedly changed in the second-hand market, and even picked out from foreign garbage, they can still be used normally, which shows their durability.
Many users talk about the performance of the multimeter, often focusing on the accuracy of the product. In fact, the security of the product is more important, and it is closely related to the user’s personal safety. It is difficult to avoid accidental operation. In the case of overload or incorrect setting, the multimeter can guarantee to avoid personal injury to the user and keep the safety of the instrument itself, which is related to the safety design of the product. More than one design margin will cost more, but it will be more secure. Strict implementation of safety standards is responsible for life.
High-end multimeters often use expensive fuses. For example, the price of a fuse in the high-end series of Fluke is more than 60 yuan. The price of a fuse can completely buy one or two cheap multimeters. High-performance, high-response fuses are more sensitive and fast to isolate overload accidents, minimize the possibility of explosions, melts, etc. due to severe overload, and the internal resistance of the fuse tube itself is extremely low. The effect of stringing into the circuit is minimal.
The extended function is the performance of the modern digital multimeter. In addition to the traditional basic measurement of voltage, current and resistance, common extended measurement functions include on-off measurement, diode measurement, triode measurement, capacitance measurement, temperature measurement, frequency measurement, duty cycle measurement, maximum value retention, and simulation. Pointer quick response display, built-in anti-interference low-pass filter, PC communication interface, and misoperation protection. The extended measurement function can sometimes replace some special instruments, expand the application range of the multimeter, achieve a multi-purpose table, and improve work efficiency and automation rate.
The brand is the guarantee of the quality of the multimeter, and it is also the embodiment of the product grade. A well-known brand is the accumulation of the market after many years, and is also the commitment of manufacturers to users. Although the low-end multimeters of some international famous brands are not brilliant in the measurement accuracy and expansion functions that the mass users pay attention to, they are relatively solid in terms of product reliability, stability, safety characteristics and other intrinsic qualities that are not often valued by users. Meticulous. Users can use it for a long time to realize the meaning of high quality products. Many users like to compare the performance of products by comparing parameters. The authenticity of the product parameters provided by famous big brands is more secure.
As the saying goes, “interlacing is like a mountain.” In the era of industrial development, the division of the industry has become more and more refined, and the technologies involved have become more and more professional and narrow. In the same electronics industry, the masters of electrical maintenance are generally not proficient in instrumentation expertise, and most of them stay at the stage of instrument application, so most multimeter users do not have in-depth understanding of the product like the industry insiders of the multimeter manufacturing industry. It is also unrealistic to become a multimeter expert to buy a multimeter. Ordinary basic knowledge plus brand guarantee is a shortcut to purchase, because the factory has designed a series of different grades for different grades of application from a professional perspective. Trust in the brand is widely accepted in the electronics industry. When you come up with a high-end brand-name multimeter, people who know it will naturally add a little trust to your test results and also recognize your professionalism.
The design is related to the durability, indestructibility, and operational certification of the multimeter. As the multimeter’s service life increases, the error becomes larger. At this time, professional calibration is needed to re-improve the measurement accuracy of the multimeter and reduce the error. For the current mainstream digital multimeter, this kind of calibration often only needs to cooperate with special instruments to perform software calibration on the data in the machine. The calibrated multimeter can fully meet the performance of the new product, and the cost of calibration is far lower than the purchase. The cost of the new form. The professional calibration can greatly increase the life of the multimeter, thus reducing the cost of the instrument. In addition to maintenance and calibration, high-end after-sales services include advanced services such as technical support.
Pointer multimeter purchase
The high-quality pointer multimeter should have a high-quality mechanical head, flexible and durable gear dials, stable system accuracy, high voltage resistance, internal resistance, complete protection mechanism, and rugged housing. The high-quality pointer head has a good response speed and has appropriate damping characteristics. Some high-grade dials are also equipped with mirror strips to reduce readout errors. Generally, a large-area dial is easier to read, but for a small portable multimeter, the overall volume of the product should also be considered. The current-grade application-grade products of domestic pointer multimeters have a DC accuracy of 2.5, and a small number of scientific-grade products have reached 1.5 and 1.0. The higher-level pointers are mostly dedicated to single-function single-range, and the actual application is 2.5. The table is enough.
In the era of digital multimeters, high-precision measurement is already the world of digital meters, and the practical significance of high-end pointers is declining. Some users think that the multimeters produced in the early stage use a large number of high-precision wirewound resistors, and the inside of the back cover is full, and the multimeters produced in recent years use the color ring resistors commonly available on the market to disassemble the interior of the back cover, so the quality Declining, new products are not good, but it is not entirely true. Early multimeters used wirewound resistors because the accuracy of the carbon film resistor was not good enough at the time, and it was easier to obtain a resistor with a small resistance error by the conventional wire winding method. Over time, the accuracy of the current color ring resistance (carbon film resistance and metal oxide film resistance) is greatly improved. With the secondary screening, it is easy to obtain the resistance that meets the error requirement, and the price of the color ring resistance is cheaper than the wire wound resistance. Many, so the use of color ring resistance is an inevitable trend. Appearance The seemingly similar color ring resistance is also graded, including the accuracy level and stability level. As long as the product is properly adjusted, it can produce a multimeter that meets the technical specifications.
The high-end products featured in the domestic pointer multimeter are: MF35 and MF18 with DC accuracy of 1.0, MF12 and MF14 with DC accuracy of 1.5, with 10 microamp test block and DC internal resistance up to 100kΩ/V. High sensitivity MF10 type. These multimeters represent the highest level of this country’s pointer table, and have a certain collection value, especially some old factory watches.
However, the use value of these high-end performances is not high. This is because these pointers, which were considered to be highly accurate in the past, cannot be compared with the current high-end digital meters. Users who demand high measurement accuracy should now use high-end desktop high-precision digital meters.
Digital multimeter purchase
Digital multimeters are the mainstream in the current market. Buying on demand and focusing on the quality of products is the wise choice. The average user does not have to pay too much attention to the resolution of the product (display digits). For even applications such as appliance repair, the most common three-and-a-half digit digital meter is enough. High-resolution testing is the most common case. There is no substantive help. For most users, the multimeter is practical and sufficient, and it is not necessary to buy high-priced, high-end products. Brand name is the guarantee of quality, and the mid-range products in the general product line have the highest price/performance ratio. Although the high-end products have excellent performance, in addition to the high initial purchase cost, the later use costs will be higher.
First, high-performance products consume more power and battery overhead. Secondly, the cost of consumables (such as fuses) is relatively high. For example, a fuse of FLUKE high-end multimeter has more than 60 yuan, and the loss caused by one misoperation will increase significantly. Again, the post-maintenance costs are also related to the grade of the multimeter, and the maintenance cost of the high-end multimeter is very high.
For some users who deal with high voltage and high current, the safety of the multimeter is more important than the measurement accuracy. The general high-precision multimeter is suitable for scientific and research-grade applications. Especially the desktop multimeter is more suitable for laboratory use. The true multimeter with more than seven and a half ultra-high precision requires strict specifications, including proper temperature and humidity. It needs to be regularly calibrated. If it is placed as casually as a normal multimeter, it will be used at startup and it will lose its practical use.
From the measurement technology, there are two methods for measuring the rms value of the digital multimeter: the average rectification principle and the true rms principle. The former method has a lower cost ratio and is mainly adapted to the measurement of a sine wave. When a square wave is encountered, the reading will be too large. Although the latter method is relatively complicated to implement, the measurement of various waveforms is relatively accurate. Most middle and high-end multimeters use true RMS measurement methods. A multimeter with true rms measurement will have the word “Ture-RMS” on the meter, which has become a sign of the digital multimeter.
In addition to measurement accuracy and measurement resolution, the multimeter’s measurement performance also has a very important indicator response speed, which is the time to start measuring stable readings. This also reflects the processing power of the multimeter processor, and the high-end digital meters. Has a very fast response speed. It should be noted that this is not directly related to the speed at which the multimeter screen is refreshed. Some users complain that their digital multimeters are measuring slowly, which is related to this indicator. There are many mid-range and low-end multimeters that avoid this problem in the parameter list.
For ordinary home users, there is basically no requirement for measurement accuracy. Consider cheap and good products, such as UT33 B, which is about 30 yuan for Unid. As long as the products of regular manufacturers can be used without too much, put them in the toolbox. Needs from time to time