P stands for the degree of tolerance to environmental conditions, which is divided into four groups: P, S, A and B \ x0d \ x0d \ Attached with the basic knowledge of electric meters: \ x0d \ x0d \ the meaning of letters and numbers on the nameplate of electric meters \x0d\ 1, and the meaning of models. The type of electric meter is expressed by letters and numbers, and the contents are as follows: \ x0d \ x0d \ category code+group code+design serial number+derivative number \x0d\ 1) category code: d- electric meter \x0d\ 2) group code: indicating phase line: d- single phase; S- three-phase, three-wire active; T- three-phase four-wire active. \x0d\ Instruction: Ampere-hour meter; Class b standard; D- multifunction; F- compound interest rate; H- total consumption; J- direct flow; L- long life; M pulse; S- all-electronic; Y- advance payment; X- reactive power; Z— Maximum demand \x0d\ 3) The design serial number is expressed in Arabic numerals. Such as 862,864,201,etc. \x0d\ 4) The derivative number can be expressed in the following ways: t- dual-purpose, used for damp heat; Th- is a humid and hot zone; Ta- used in dry and tropical areas; G- platform use; h-marine； Chemical corrosion protection, etc. For example: \ x0d \ DD-for single-phase electric meters, such as DD862 and dd702 \ x0d \ ds-for three-phase three-wire active electric meters, such as DS864 and ds8 \ x0d \ dt-for three-phase four-wire active electric meters, such as DT862 and dt864 \ x0d \ dx- \ x0d \ db —— refers to standard electric meters, such as DB2, DB3\ x0d \ DBS —— refers to three-phase three-wire standard electric meters, such as DBS25\x0d\ DZ— —— indicates the maximum demand electric meters, such as DZ 1, \ x0d \ DBT —— indicates the three-phase four-wire active standard meter, such as \ x0d \ dssd —— refers to a three-phase three-wire fully electronic multifunctional electric meter, such as dssd331; \ x0d \ ddy —— indicates a single-phase prepayment meter, such as DDY59\x0d\ 2. Nameplate logo: \x0d\ 1) trademark. \x0d\ 2) Measurement License Mark (CMC). \x0d\ 3) Name or symbol of measurement unit, such as "kW" for active watt-hour meter? "or" kWh "; Is the reactive power meter "kW"? "or" kval ". \x0d\ 4) In the window of the V-wheel counter, different colors are used to distinguish between integer digits and decimal digits, with a decimal point in the middle; Without decimal places, each character wheel in the window has a multiplication factor, such as × 1000, × 100, × 10, × 1. \x0d\ Meter name and model \x0d\ 5) Basic current and rated maximum current. The basic current (also called calibration current) is the current value that determines the relevant characteristics of the meter, which is expressed by Ib; The rated maximum current is the maximum current value that the instrument can meet the precision specified in its manufacturing standard, and is expressed by Imax. \x0d\ 6) Reference voltage. Refers to the voltage value that determines the relevant characteristics of the electric meter, expressed by UN. For a three-phase three-wire meter, it is expressed by multiplying the number of phases by the line voltage, such as 3× 380 V; For a three-phase four-wire meter, it is expressed by multiplying the phase number by the phase voltage/line voltage, such as 3× 220/380 V; For single-phase meters, it is expressed by the voltage at the voltage line terminal, such as 220V V. \x0d\ 7) reference frequency. Refers to the frequency value that determines the relevant characteristics of the electric meter, expressed in hertz (Hz). \x0d\ 8) meter constant. Refers to the constant of the relationship between the electric energy recorded by the electric meter and the corresponding number of revolutions or pulses. The active watt-hour meter is expressed in kWh/r(imp) or r(imp)/kWh; The reactive power meter is expressed as kvarh/r(imp) or r(imp)/kvarh. These two constants are reciprocal. \x0d\ 9) accuracy level. The symbols of the number of phases and lines are represented by the series recorded in the circle. \x0d\ 1 1) The ability to withstand environmental conditions is divided into four groups: P, S, A and B. \x0d\ 12) Manufacturing standard. \x0d\ 13) Name or address of the manufacturer. \x0d\ 14) year of manufacture. \x0d\ 15) If the instrument is equipped with a backstop, it is marked with a bar code: backstop \x0d\ 16). \x0d\ 17) factory number. \ x0d \ \ x0d \ d- used in the front to indicate the electric energy meter, such as DD862；; Used in the back to indicate multifunction, such as dtsd 855 \ x0d \ DD- single phase, such as DD 862 \ x0d \ dt- three-phase four-wire, such as dt 862 \ x0d \ ds- three-phase three-wire, such as ds 862 \ x0d \ f- compound ratio, such as ddsf855 \ x0d \ y-. \x0d\ Meaning of nameplate content of electric meter \x0d\ On the nameplate of electric meter, we can see the following terms: single-phase, three-phase, active and reactive, etc. The nameplate is also marked with the registration model: DDS×××, the first D is the pinyin prefix of "electricity meter", the second D is the pinyin prefix of "single phase", and S is the prefix of "static (commonly known as electronic)" English static. "×××××" represents different types of electric meters produced by different enterprises. China adopts a voltage system of 220V, and the frequency of alternating current is 50Hz. Pay special attention to the marked current values: for example, 5(20)A means that the basic current is 5A and the maximum current is 20A. Overloading electricity is unsafe and a fire hazard. \x0d\ Meter Grade \x0d\ The nameplate is also marked with ① or ②, indicating that the meter accuracy is 1%, or 1 class table; (2) The accuracy of the representative instrument is 2%, or 2m. The nameplate is also marked with the standard code, manufacturer, trademark and factory number of the product. The section of 0.5 in the accuracy grade of electric meter refers to the accuracy grade of metering winding, which can reach 0.5 when the current reaches more than 10% of the rated current. S stands for wide range. When the current reaches more than 1% of the rated current, the accuracy level can reach 0.5. \x0d\ The grade of the electric meter is used to indicate the accuracy of the electric meter. China stipulates that electric meters are divided into seven grades, namely 0. 1, 0.2, 0.5, 1.0, 1.5, 2.5 and 5.0. The smaller the grade value. The higher the accuracy of the instrument. Usually, the grade of the electric meter used is marked on the dial of the electric meter. \x0d\ Why can the grade of the electric meter reflect the accuracy of the electric meter? This is because the grade of the electric meter is determined by the measurement error of the electric meter. When measuring with an electric meter, the difference Δ x between the indicated value x of the electric meter and the measured actual value X0 is called the absolute error of electric meter measurement. The ratio of the absolute error value to the range Xn of the electric meter, expressed in percentage, is called the reference error en of the electric meter, that is, en = (δ x/xn) × 100% \ x0d \ When measured by the electric meter, the maximum reference error Enm will be obtained. If you remove the% symbol, it will be the level of the instrument. If the result is between two specified grade values, the grade of the electric meter is set to low precision grade at this time. For example, if the maximum reference error of a meter is 0.7%, the rating of the meter will be 1.0 instead of 0.5. \x0d\ When measuring, the maximum absolute error can be calculated by knowing the grade and range of the electric meter used, so as to estimate the measurement accuracy. \ x0d \ x0d \ The current value before brackets is called basic current, which is used to calculate the current value of load base. The current in brackets is called rated maximum current, which is the maximum current value that can make the meter work normally for a long time, and the error and temperature rise completely meet the specified requirements. \x0d\ According to the requirements of regulations, the basic current of the direct-connected electric meter should be determined according to the rated maximum current and overload multiple, in which the rated maximum current should be determined according to the recognized customer load capacity; Overload multiple, if the actual load current of the meter reaches more than 30% of the maximum rated current during normal operation, it should be 2 times; If the actual load current is less than 30%, count 4 times. \ x0d \ x0d \ What are the symbols A, A 1, B, B 1 on the nameplate of the electric meter? When the ambient temperature changes, what effect does it have on its additional error? \x0d\\x0d\ A: symbol a indicates that the external ambient temperature used by the electric meter should be 0 ~+40℃ and the relative temperature should be 95%\x0d\ A 1 indicates that the ambient temperature is 0 ~+40℃ and the relative humidity is 85%\x0d\ B indicates that the ambient humidity is-/kloc-0. \ x0d \ x0d \ When the ambient temperature changes, the braking flux, voltage, current working flux and phase angle of the electric meter all change, thus causing additional errors. For example, when the temperature rises, the braking flux decreases, the braking torque decreases, and the speed of the electric meter increases. At the same time, the resistance of the meter turntable increases, the angle between the current working flux and the total current decreases, and the excitation component and corresponding flux of the total current increase, which makes the meter rotate faster. Moreover, the reluctance of this part of the voltage working flux decreases, which increases the voltage working flux and speeds up the speed of the electric meter. The above three actions will produce additional error of positive temperature.