Multimeter, also known as multimeter, multimeter and multimeter, is a multifunctional and multi-range measuring instrument. Multimeters can generally measure DC current, DC voltage, AC voltage, resistance, audio level, and some can also measure AC current, capacitance, inductance and some parameters of semiconductors (such as β).
1.[ Edit this paragraph] Structure of multimeter
(Model 500)
The multimeter consists of three main parts: meter head, measuring circuit and transfer switch.
(1) ammeter: It is a high-sensitivity magnetoelectric DC ammeter, and the main performance indexes of multimeter basically depend on the performance of ammeter. The sensitivity of the instrument refers to the DC current value flowing through the instrument when the pointer of the instrument deflects at full scale. The smaller the value, the higher the sensitivity of the blood glucose meter. When measuring voltage, the greater the internal resistance, the better its performance. There are four scale lines on the meter head, and their functions are as follows: The first line (from top to bottom) is marked with R or Ω, indicating the resistance value. When the changeover switch is in the ohm range, read the scale line. The second line is marked with ∽ and VA, indicating the values of AC and DC voltages and DC currents. When the change-over switch is in the range of AC, DC voltage or DC current, and the measuring range is in other positions except AC 10V, read the scale line. The third line is marked with 10V, indicating that the AC voltage value is 10V. When the change-over switch is in the AC and DC voltage range, read the scale line. The fourth mark is dB, which indicates the audio level.
(2) Measuring circuit
The measuring circuit is used to convert various measured signals into tiny DC current suitable for electric meter measurement. It consists of resistors, semiconductor components and batteries.
It can convert all kinds of measured data (such as current, voltage, resistance, etc.). ) and different measuring ranges are converted into a certain amount of micro DC current after a series of treatments (such as rectification, shunt, voltage division, etc.). ) and send it to the meter for measurement.
(3) Transfer switch
Its function is to select different measuring lines to meet the measurement requirements of different types and ranges. Generally, there are two transfer switches marked with different gears and ranges.
2.[ Edit this paragraph] Symbolic meaning of multimeter
(1)~ stands for AC and DC.
(2) V-2.5kV 4000Ω/V means that the sensitivity of AC voltage and 2.5kV DC voltage block is 4000Ω/V..
(3)A-V-ω represents measurable current, voltage and resistance.
(4) 45-65- 1000 Hz means that the frequency range is below 1000 Hz and the standard power frequency range is 45-65 Hz.
(5) 2000Ω/V DC means that the sensitivity of DC gear is 2000Ω/V.
The symbols on the pliers table and dial are similar to the above symbols (others can't all be written as "Indicating Magnetoelectric Rectifier with Mechanical Reaction" to indicate the prevention of the third-level external magnetic field and "Indicating Horizontal Placement" because of the wrong symbol format).
3. Be careful when using ohmmeter, and pay attention to uneven scale. [Edit this paragraph] The use of multimeter
(1) Be familiar with the meaning of each symbol on the dial and the main functions of each knob and selector switch.
(2) Perform mechanical zero adjustment.
(3) According to the type and size of measurement, select the gear and range of transfer switch, and find out the corresponding scale line.
(4) Select the position of the probe jack.
(5) Measuring voltage: Choose a good range when measuring voltage (or current). If the large voltage is measured with a small range, there is a danger of burning the meter; If a small voltage is measured in a large range, the pointer deflection is too small to read. When selecting the measuring range, the pointer should be deflected to about 2/3 of the full scale. If the measured voltage is not known in advance, the highest range block should be selected first, and then gradually reduced to the appropriate range.
A. Measurement of AC voltage: Put one change-over switch of multimeter in AC and DC voltage range, and the other change-over switch in proper AC voltage range. The two probes of the multimeter are connected in parallel with the tested circuit or load.
B. DC voltage measurement: put one switch of the multimeter in the range of AC and DC voltage, the other switch in the appropriate range of DC voltage, connect the "+"pin (red pin) to high potential, and connect the "-"pin (black pin) to low potential, that is, let the current flow in from the "+"pin and out from the "-"pin. If the stylus is connected backwards, the pointer on the meter will deflect in the opposite direction, and it is easy to bump the pointer.
(6) Current measurement: When measuring DC current, put one change-over switch of multimeter in DC current range and the other change-over switch in the appropriate range of 50uA to 500mA. The range selection and reading method of current are the same as that of voltage. When measuring, the circuit must be disconnected first, and then the multimeter is connected in series to the circuit under test in the direction from "+"to "-",that is, the current flows in from the red stylus and out from the black stylus. If the multimeter is mistakenly connected in parallel with the load, the internal resistance of the meter is very small, which will cause short circuit and burn out the instrument. The reading method is as follows:
Actual value = indicated value × range/full deviation
(7) Resistance measurement: When measuring resistance with multimeter, the following methods should be adopted:
Mechanical zero adjustment. Before use, the pointer positioning screw should be adjusted to make the current indication zero to avoid unnecessary errors.
Select the appropriate magnification. The scale line of the multimeter's ohm gear is uneven, so choose the multiplier gear to make the pointer stay in the thinner part of the scale line. The closer the pointer is to the middle of the scale, the more accurate the reading will be. Generally speaking, the pointer should be between 1/3 and 2/3 of the scale.
C ohm zero adjustment. Before measuring the resistance, the two probes should be shorted together, and at the same time, the "ohm (electric) zero adjustment knob" should be adjusted so that the pointer just points to the zero position on the right side of the ohm scale line. If the pointer is not set to zero, it means that the battery voltage is insufficient or there is a problem inside the instrument. Moreover, every time the amplification gear is changed, ohmic zero adjustment should be carried out again to ensure the accuracy of measurement.
D reading: the reading of the instrument multiplied by the magnification is the resistance value of the measured resistor.
(8) Precautions
A when measuring current and voltage, you can't change the range with electricity.
B. When selecting the measuring range, choose the large one first, then the small one, and try to make the measured value close to the measuring range.
C when measuring resistance, can't live measurement. Because when measuring resistance, the multimeter is powered by an internal battery. If it is charged, it is equivalent to connecting an extra power supply, which may damage the meter.
D after use, the change-over switch should be at the maximum position or neutral position of AC voltage.
E note that when changing the range of ohmmeter, it is necessary to carry out ohmic zero adjustment, and mechanical zero adjustment is not required. [Edit this paragraph] Digital multimeter
Now, digital measuring instruments have become the mainstream and have replaced analog instruments. Compared with analog instruments, digital instruments have the advantages of high sensitivity, high precision, clear display, strong overload capacity, convenient carrying and simpler use. Taking Festek FT368 digital multimeter as an example, this paper briefly introduces the significance of its specific parameters, usage and matters needing attention.
Basic features:
? 1, 44/5-bit true rms multimeter, maximum display number: 49999;
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2. GJB industrial design quality national military standard
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3. Ultra-wide frequency response range up to 200KHz, wide measurement range of capacitance and resistance, and more powerful function;
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4. The basic DC accuracy is 0.025%, and the true root mean square measurement makes the data more accurate;
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5. Equipped with USB interface, data transmission is more convenient, and trend drawing can be realized by using FaithtechView software.
Data viewing, real-time observation, logic analysis, single-channel oscillometric function and harmonic analysis.
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6, with AC voltage, DC voltage, AC current, DC current, resistance, capacitance, diode, pass.
Measurement functions, such as discontinuity, frequency, temperature, duty ratio, pulse width, relative value, dBV, dBmV and conductance;
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7. Fast, minimum and maximum modes can capture the instantaneous signal of 0.25ms very quickly;
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? 8. Patented design: manual or automatic diode screening voltage setting;
(1) usage
A. Before use, please read the relevant instructions carefully and be familiar with the functions of the cutter head, button and jack.
Close the cutter head and start the machine.
C basic measurement: dial the corresponding position as needed. Measurement of AC /DC voltage: directly display the mainstream component and AC component of mixed signal, and insert the stylus into the corresponding jack.
D Other functions such as temperature measurement, diode selection, temperature measurement, frequency, duty ratio, fast pulse, dB, logic analysis, oscilloscope, trend chart, harmonic analysis, on-off performance, conductance, capacitance, etc. can be realized.
(2) Precautions for use
The current jack is used to measure the current. Do not use this jack when not in use, or the multimeter may be burned.
The cat range of the multimeter is automatic. If you want to use the specified range, press the range selection key.
When the wrong jack is inserted, the multimeter will give an alarm. When using the functions of trend chart, oscilloscope, logic analysis and harmonic analysis, please check the range selection and cutter head position. [Edit this paragraph] Shake your watch.
Megohmmeter, also known as megohmmeter, is an instrument used to measure the insulation resistance and high-value resistance of the equipment under test. It consists of a hand-cranked generator, a meter head and three terminals (namely, L: line terminal, E: grounding terminal and G: shielding terminal).
1. Selection principle of vibration table
(1) Selection of rated voltage level. In general, for equipment with rated voltage below 500V, 500V or 1000V shaking table should be selected; For equipment with rated voltage above 500V, choose 1000V~2500V shaking table.
(2) Selection of resistance range. There are two small black dots on the dial scale line of the shaking table, and the area between the small black dots is the accurate measurement area. Therefore, when selecting instruments, the insulation resistance value of the tested equipment should be within the accurate measurement area.
2. Use of shaker
(1) Check the form. Before measurement, the shaking table should be tested for open circuit and short circuit to check whether the shaking table is in good condition. Open two connecting wires and shake the handle. The pointer should point to ∞, and then short two connecting wires. The pointer should point to "0", so long as the above conditions are met, otherwise it cannot be used.
(2) The equipment under test is disconnected from the line, and the equipment with large capacitance needs to be discharged.
(3) Choose a shaking table with voltage grade.
(4) When measuring the insulation resistance, generally only "L" and "E" terminals are used, but when measuring the insulation resistance of cables to the ground or the leakage current of the equipment under test is serious, the "G" terminal should be used and connected to the shielding layer or shell. After the wire is connected, you can rotate the crank clockwise, and the speed of shaking should be fast and slow. When the rotating speed reaches about 120 revolutions per minute (ZC-25 model), keep rotating at a constant speed, read after 1 minute, and read while shaking, without stopping reading.
(5) Take out stitches and leave the hospital. After reading it, shake it slowly, take out the suture, and then discharge the device under test. The discharge method is to remove the grounding wire for measurement from the shaking table and simply connect it with the measured equipment (not shaking table discharge).
4. Preventive measures
(1) It is forbidden to measure insulation resistance when lightning strikes or near high-voltage equipment, and it can only be measured when the equipment is not charged and there is no induced electricity.
(2) During the shaking test, no one is allowed to work on the tested equipment.
(3) The shaking table wires should not be twisted together, but should be separated.
(4) It is forbidden to touch the shaking table by hand before the shaking table stops rotating or before the device under test discharges. Don't touch the metal part of the wire when removing it.
(5) At the end of measurement, discharge the equipment with large capacitance.
(6) Check its accuracy regularly.
Three. [Edit this paragraph] Clamping table
Clamp meter is an instrument used to measure the current of running electrical lines, which can continuously measure the current.
1. Structure and principle
The clamp meter is mainly composed of current transformer, clamp wrench and rectifier magnetoelectric instrument with reaction force.
2. Method of use
(1) Mechanical zero adjustment is required before measurement.
(2) Choose a suitable range, first choose a large range, then choose a small range or look at the nameplate value estimation.
(3) Measure with the minimum range. When the reading is not obvious, the measured wire can be wound several times, and the number of turns will be subject to the number of turns in the center of the jaw, so the reading = indicated value × range/full deviation × turns.
(4) When measuring, the measured wire should be in the center of the jaw, and the jaw should be closed to reduce the error.
(5) After measurement, place the transfer switch at the maximum position of the measuring range.
3. Preventive measures
(1) The voltage of the tested line is lower than the rated voltage of the clamp meter.
(2) When measuring the high voltage line current, wear insulating gloves, shoes and stand on the insulating mat.
(3) The jaws should be closed, and the range cannot be changed by charging.
Comparison between pointer multimeter and Digital Multimeter
Pointer and digital multimeter have their own advantages and disadvantages. Pointer multimeter is an ordinary instrument, and its reading indication is intuitive and vivid. The general reading is closely related to the swing angle of the pointer, so it is more intuitive. Digital multimeter is an instantaneous sampling instrument. It samples every 0.3 seconds to display the measurement results, sometimes the results of each sampling are only very close, not exactly the same, and the reading results are not as convenient as the pointer. Pointer multimeter generally has no amplifier, so the internal resistance is small. For example, the DC voltage sensitivity of MF- 10 model is100 kω/V ... The DC voltage sensitivity of MF-500 model is 20 kω/V. Due to the internal operational amplifier circuit, the internal resistance of the digital multimeter can be very large, usually 1mω or more. (i.e. higher sensitivity can be obtained). This makes the influence on the tested circuit smaller and the measurement accuracy higher. Because of the low internal resistance, pointer multimeter mostly uses discrete components to form shunt and voltage divider circuits. Therefore, the frequency characteristics are not uniform (relative to numbers), while the frequency characteristics of pointer multimeter are relatively better. Pointer multimeter has simple internal structure, so it has lower cost, fewer functions, simple maintenance and strong over-current and over-voltage capability. Digital multimeter adopts oscillation, amplification, frequency division protection and other circuits, so it has many functions. For example, it can measure temperature, frequency (in a low range), capacitance and inductance, and can be used as a signal generator and so on. Digital multimeters have poor overload capability due to the internal structure of integrated circuits (although some of them can automatically shift gears and protect themselves, but it is more complicated to use), and it is generally not easy to repair after being damaged. The output voltage of digital multimeter is low (generally less than 1V). It is not convenient to test some components with special voltage characteristics (such as SCR, LED, etc.). ). The output voltage of pointer multimeter is relatively high (10.5V, 12V, etc. ). The current is also large (for example, MF-500* 1 Euromax 100 mA), which is convenient for testing silicon controlled rectifier and light emitting diode. Beginners use pointer multimeter, and non-novices use two kinds of watches.
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A, the choice of pointer table and digital table:
1, the reading accuracy of the pointer meter is poor, but the process of pointer swing is intuitive, and its swing speed and amplitude can sometimes objectively reflect the measured size (for example, slight jitter when transmitting data on the television data bus (SDL)); The reading of digital meter is intuitive, but the process of digital change looks messy and difficult to watch.
2. Generally, the pointer instrument has two batteries, one is 1.5V low voltage and the other is 9V or 15V high voltage, and its black stylus is the positive terminal relative to the red stylus. Digital instruments usually use 6V or 9V batteries. In the range of resistance, the stylus output current of pointer instrument is much larger than that of digital instrument. Using the range of r×1Ω can make the speaker emit a loud "beep" sound, and using the range of r×1Ω can even light up the light emitting diode (LED).
3. In the voltage range, the internal resistance of pointer instrument is smaller than that of digital instrument, and the measurement accuracy is relatively poor. In some cases, it is even impossible to measure high-voltage micro-current, because its internal resistance will affect the circuit under test (for example, when measuring the voltage of the acceleration stage of TV picture tube, the measured value will be much lower than the actual value). The internal resistance of digital meter voltage file is very large, at least in the order of megaohms, which has little influence on the circuit under test. However, the extremely high output impedance makes it vulnerable to the induced voltage, and the measured data may be false in some occasions with strong electromagnetic interference.
4. In short, the pointer instrument is suitable for the measurement of analog circuits with relatively large current and voltage, such as televisions and audio amplifiers. It is suitable for digital circuit measurement of low voltage and small current such as BP machine and mobile phone. Not absolutely, you can choose the pointer table and the digital table according to the situation.
Second, the measurement skills (if not specified, refers to the pointer table):
1. speaker measurement, earphone, dynamic microphone: use r×1Ω file, with one stylus connected to one end and the other stylus touching the other end. Under normal circumstances, it will make a crisp "beep" sound. If it doesn't ring, the coil is broken. If the noise is very small and sharp, there is a problem with wiping the coil and it cannot be used.
2. Capacitance measurement: Use a resistor to select an appropriate measurement range according to the capacitance, and pay attention to connecting the black contact pin of electrolytic capacitor to the positive electrode of capacitor during measurement. ① Estimation of microwave capacitor capacity: According to the maximum amplitude of pointer swing, it can be judged by experience or reference to standard capacitors with the same capacity. Reference capacitors do not have to have the same withstand voltage, as long as they have the same capacity. For example, it is estimated that a capacitance of 100μF/250V can refer to a capacitance of 100μF/25V. As long as the maximum amplitude of their pointer swings is the same, it can be concluded that the capacitance is the same. ② estimation of picofarad capacitance: r×10kΩ should be adopted, but only the capacitance above 1000pF can be measured. For the capacitance of 1000pF or a little larger, you can think that the capacity is enough as long as you swing your hands a little. (3) Measuring whether the capacitor is leaking: For the capacitor above 1000 microfarads, you can use the r×10Ω file to quickly charge, preliminarily estimate the capacitor, and then switch to the r×1kΩ file to continue the measurement for a period of time. At this time, the pointer should not return, but should stop at or very close to ∞, otherwise there will be leakage. For some timing or oscillating capacitors below tens of microfarads (such as the oscillating capacitor of color TV switching power supply), the leakage characteristics are very high, so it can not be used as long as there is a little leakage. At this time, it can be used for r× 1kω file after charging, and then it can be used for continuous measurement. Similarly, the pointer should stop at ∞ and should not return.
3. On-road test of diodes, triodes and voltage regulators: Because in actual circuits, the bias resistance of triodes or the peripheral resistance of diodes and voltage regulators are generally relatively large, mostly above several hundred thousand ohms, so we can use the r×10Ω or r×1Ω file of multimeter to measure the quality of PN junction on the road. In road measurement, the PN junction measured with r× 10ω gear should have obvious positive and negative characteristics (if the difference between positive and negative resistances is not obvious, it can be measured with r× 1ω gear). Generally, when measuring with R×10Ω file, the forward resistance should be indicated to be around 200Ω, and measured with R×1Ω file. If the measurement results show that the forward resistance is too large or the reverse resistance is too small, it means that there is something wrong with this PN junction and this lamp tube. This method is particularly effective for maintenance, which can find out the bad pipes very quickly, and even detect the pipes that are not completely broken but whose characteristics have deteriorated. For example, if you measure the forward resistance of PN junction with a small resistance file, it may be normal if you weld it down and re-measure it with the commonly used r× 1kω file. In fact, the characteristics of this tube have deteriorated, and it can't work normally or is unstable.
4. Resistance measurement: It is very important to choose a good measuring range. When the pointer indicates the full range 1/3 ~ 2/3, the measurement accuracy is the highest and the reading is the most accurate. It should be noted that when measuring megohm resistance with R× 10k resistor, fingers should not be clamped at both ends of the resistance, which will make the measurement result smaller.
5. Measuring the zener diode: The voltage stabilizing value of the commonly used zener diode is generally greater than 1.5V, and the resistance range of the pointer instrument below R× 1k is powered by the 1.5V battery in the instrument. In this way, the voltage stabilizing tube with the measuring resistance below R× 1k has complete unilateral conductivity just like the measuring diode. The R× 10k gear of pointer instrument is powered by 9V or 15V battery. When measuring the voltage regulator with R× 10k, the reverse resistance will not be ∞, but there is a certain resistance, but this resistance is still much higher than the forward resistance of the voltage regulator. In this way, we can preliminarily estimate the quality of the voltage regulator. But a good voltage stabilizing tube should have an accurate voltage stabilizing value. How to estimate this regulated value under amateur conditions? Not difficult. Just find another pointer table. The method is as follows: firstly, put a meter at R× 10k, with its black and red probes connected to the cathode and anode of the voltage stabilizer respectively, then simulate the actual working state of the voltage stabilizer, and then put another meter at the voltage level of V× 10V or V×50V (according to the specified value), and connect the red and black probes to the black and white probes of the meter just now. Say "basically" because the bias current of the first meter to the voltage stabilizer is slightly smaller than that in normal use, so the measured voltage stabilizer value will be slightly larger, but the basic difference is not big. This method can only estimate the voltage stabilizing tube whose voltage stabilizing value is less than the high voltage battery voltage of pointer instrument. If the voltage stabilizing value of the voltage stabilizing tube is too high, it can only be measured by the method of external power supply (in this way, when we choose the index, it is more suitable to choose the high-voltage battery voltage of 15V than 9V).
6. Measuring triode: We generally use r× 1kω. Whether NPN or PNP transistors, whether low power, medium power or high power transistors, cb junction of be junction should show the same unidirectional conductivity as diode, with infinite reverse resistance and forward resistance of about 10K. In order to further estimate the characteristics of the pipe, it is necessary to change the resistance gear for multiple measurements. The method is as follows: set the r×10Ω gear, and measure the forward on-resistance of PN junction, which is about 200Ω; Set r× 1ω to measure the forward on-resistance of PN junction, all of which are about 30ω. (The above data were measured with Model 47 instrument, and other models are slightly different. You can try several good tubes to summarize. If the reading is too large, it can be concluded that the characteristics of the lamp are not good. You can also put the meter at r×10Ω and retest. For tubes with low withstand voltage (basically, the withstand voltage of transistors is above 30V), the reverse resistance of cb junction should also be ∞, but the reverse resistance of BE junction may be a little, and the pointer of the instrument will slightly shift (generally it will not exceed 1/3 of full scale, depending on the withstand voltage of the tube). Similarly, when measuring the resistance between ec (for NPN tube) or ce (for PNP tube) with r× 10kω, the pointer may slightly shift, but this does not mean that the tube is not good. But when measuring the resistance between ce and ec with r× 1kω, the indication on the instrument should be infinite, otherwise there is something wrong with the pipeline. It should be noted that the above measurements are for silicon tubes, not germanium tubes. But germanium tubes are rare now. In addition, the so-called "reverse direction" refers to the PN junction, and the direction of NPN tube and PNP tube is actually different.
Nowadays, most common triodes are plastic-sealed. How to accurately judge which of the three pins of a triode are B, C and E? The B pole of triode is easy to measure, but how to determine which is C and which is E? Three methods are recommended here: the first method: for the pointer instrument with transistor hFE socket, first measure the B pole, then insert the transistor into the socket at will (of course, the B pole can also be inserted accurately), measure the hFE value, and then measure the lamp tube again in reverse. When the hFE value is relatively large, the insertion position of each pin is correct. The second method: For the meter without hFE measuring jack, or the meter with too large tube to be inserted into the jack, you can use this method: For the NPN tube, measure the B pole first (whether the tube is NPN or PNP, its B pin is easy to measure, right? ), put the watch into the r×1kΩ file, connect the red stylus to the imaginary E pole (be careful not to touch the pen tip or pin of the watch), and connect the black stylus to the imaginary C pole. At the same time, hold the nib and pin with your fingers, pick up the tube, and lick the B pole with your tongue. You should see that the pointer on the instrument should have a certain deflection. If the pen is connected correctly, the pointer deflection will be greater. Therefore, the C and E poles of the pipeline can be determined. For PNP tube, connect the black stylus to the hypothetical E pole (do not touch the pen tip or pin) and connect the red stylus to the hypothetical C pole. Hold the nib and this pin with your fingers at the same time, and then lick the B pole with the tip of your tongue. If the pen is connected correctly, the pointer on the meter head will deviate greatly. Of course, when measuring, the pen and the pen should be exchanged twice, and the final judgment can only be made after comparing the readings. This method is suitable for all shapes of transistors, which is convenient and practical. According to the deflection amplitude of the watch hand, the amplification ability of the electron tube can also be estimated, which is of course based on experience. The third method: first determine the NPN or PNP type of the pipeline and its B pole, and then put the electric meter into the r×10kΩ file. For NPN tube, when the black contact pin is connected to the E pole and the red contact pin is connected to the C pole, the instrument pointer may be deflected to some extent. For PNP tube, when the black stylus is connected to the C pole and the red stylus is connected to the E pole, the instrument pointer may be deflected to some extent, and vice versa. Therefore, the C and E poles of the triode can also be determined. However, this method is not suitable for high-pressure resistant pipelines.
Common imported high-power plastic sealing pipes, the C pole is basically in the middle (B is never seen in the middle). Some B's of small and medium power tubes are probably in the middle. For example, the commonly used 90 14 transistor and its series of other types of transistors, 2SC 18 15, 2N540 1, 2N555 1, etc. There are some B poles in the middle. Of course, there is also a C pole among them. Therefore, when repairing and replacing triodes, especially these low-power triodes, do not install them directly, but must test them first.
SK-ZJF-7 [1] On-site multimeter simulator for automatic instrument is a hand-held comprehensive digital calibrator with high precision, high resolution, high reliability and anti-drop performance, which integrates the functions of digital display DC voltage, millivolt and current signal source and digital multimeter. The instrument adopts a large LCD with a height of 22mm, and the reading is clear. At the same time, the instrument also has an EL backlight for reading in dark places. The instrument supplies power for AC and DC, making it more convenient to use.
The functions of instrument signal output and milliampere and millivolt measurement are mainly designed to meet the needs of field calibration and maintenance of industrial automation field instruments. The instrument also has the general function of multimeter, and is an ideal tool for field instrument workers, computer distributed control system maintenance personnel and instrument installation personnel. It is different from the general electric multimeter and signal source, and it is the multimeter of instrument workers.
The circuit design of the whole machine is based on large-scale integrated circuit double integral A/D converter, which has the functions of signal output and test. Its technical performance conforms to the calibration standard of electrical II and III automatic instruments, and its working environment conforms to the relevant provisions of Group II instruments in GB6587. 1-86 "Environmental Test Outline of Electronic Measuring Instruments".
I. Functions and Features
*4 1/2 LCD screens with word height of 22mm.
* The over-range display is "1", and the maximum display value is 19999.
*24V。 DC(30 ma. Maximum) power output, which can be used as 24V. DC working power supply of two-wire instrument.
* There are 0- 10V, 0- 100mV, 0-20mV, 0-20mA and 0-22mA DC signal sources, which can simulate the output signals of various II and III instruments during field calibration.
* 0~20KHz frequency output.
* there are 200mV, 2V, 20V, 200V and 700V DC voltage signal measurement files.
* 20mA, 100mA DC current signal measurement file.
* There are measurement files for 2V, 20V, 200V and 700V AC voltage signals.
* There are 20mA, 100mA AC current measurement files.
* There are 200Ω, 2kΩ, 20KΩ, 200KΩ, 2m Ω and 20MΩ resistance measurement files.
* There is diode voltage drop and line on-off gear.
* There are 20KHz frequency measurement files.
* EL backlight, suitable for reading in dark places.
* Use large-capacity battery packs. When the battery is low, ""will be displayed in the upper left corner of the LCD.
* A sealed enclosure was designed according to international safety standards, and the battery cover was removed.
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