Monday, February 7, 2011

【 Weak current College 】 (universal table) the use of a multimeter (upper) 】

Multimeter is the measurement of resistance, voltage, current, and audio power equal meter. A measuring resistance
In the measurement of resistance, should be marked with a "tick" Ω at reading (because of electricity through the header and the measured resistance is not a proportional relationship, so dial scale of resistance is not uniform in size. ) Is the actual value of the measured resistance is equal to the scale ruler reading multiplied by the multiplier knob. In the survey before you will receive two table pen short, rotating zero potentiometer, the pointer in the location of the 0 Ω, and then choose the right gear to ensure accurate measurement. The amount of each change, all to zero. In addition, the resistance measurements, be sure to passive and no other parallel branches. Resistor (or current) measurement has been completed, should be to high voltage switch-gear, this is to prevent the misuse of an ohmmeter (or the current block) measuring voltage of good habits.
B DC voltage and current measurement
Reading should be at the "DC" or "V · mA" symbol scale table, at which point the knob is a DC voltage or current maximum limit (range). Measurement before estimated by measuring the size of the value, then will switch to the appropriate range of stalls. Proportional to the size of the measurement values are read out. Measure the voltage between two points on the circuit, the red pen should meet the test of high potentials, black test pen should receive low potential. Measuring DC current to the ammeter series into the branch, you must first disconnect the measured tributary. If you do not disconnect the slip road take two passengers into the slip road to the table amount of endpoints, actually is used to measure voltage, amperemeter, electricity is consumed.
Multimeter judged the quality of the capacitor
Depending on the electrolytic capacitor size, usually chosen multimeter R× R× 10, 100, R×1K retaining test judgement. Red and black tablepens respectively the negative terminal of the capacitor (before each test, the capacitor discharge), the needle by tilting the table to determine the quality of the capacitor. If the hands quickly swing up to the right, and then return slowly to the left in situ, the capacitor is generally good. If the table is no longer a Cycloid after starting, the capacitor has a rotary breakdown. If the table after the Cycloid up gradually return to a position of stop bits, then the capacitor has leakage. If the table Cycloid, explains capacitor electrolytic push lost capacity has run dry. Some of the leakage of capacitors, using the methods above are not easy to accurately figure out good or bad. When the capacitor voltage value is greater than the multimeter battery voltage value in, according to a Electrolytic Capacitor is charging leakage current is small, the reverse charge leakage current major characteristic, use the R×10K retaining, reverse charging capacitor, look at the table whether the needle stays stable (i.e. reverse leakage current is a constant), which determine the quality, accuracy of capacitor is relatively high. Black table amount received the negative terminal of the capacitor, red table amount received capacitor cathode, hands quickly swing up, and then gradually return to a stationary, then the capacitor is good, all hands in a location remain unstable or stay later gradually and slowly move to the right of the capacitor has leakage, could not continue to use. Hands remain stable in General and 50-200K scale range.
Multimeter as detection tools detect method of integrated circuit
Although IC substitution as well, but after all, a demolition. Therefore, the precise judgement before breaking circuits are you sure that is corrupted and the extent of the damage, and avoid blind demolition. This article describes only the multimeter as detection tools is not on the road and road testing methods and considerations of integrated circuits. Described in theroad test of the four methods (DC resistance, voltage, AC voltage and current measurement of the total) is the amateur service useful and frequently used detection method.    Here, I hope you will provide other useful (IC and component) discrimination testing experience. First, not in the road test this method is in the IC is not welded into the circuit when, under normal circumstances the PIN available multimeter measurement corresponds to the grounding pin between active, reactive and resistance, and good IC.   Second, in the road test this is a means of detecting the PIN IC multimeter in road (IC in circuit) DC resistance, AC and DC voltage to ground, as well as the total work current detection method. This approach overcomes the substitution test method requires the limitations of the IC can be substitution and the demolition of the IC, IC is to detect the most common and practical way.  1. on the road of DC resistance test method a multimeter ohmmeter, directly at the Board of the PIN on the measurement IC and external components of forward and backward DC resistance, and compared with normal data, to identify and determine whether the failure of the method.  Measuring time to pay attention to the following three points: (1) measurements before you disconnect the power supply, so as not to damage the meter and test components.   (2) internal electrostatic barrier multimeter voltage not greater than the best available 6V, quantum R× 100 or R×1k retaining. (3) measurement IC PIN parameter, it is necessary to pay attention to measuring conditions, such as the tested machine type, and IC related potentiometer, sliding arm position but also peripheral circuit elements. 2. DC voltage measurement is in power, multimeter DC voltage supply voltage to the DC block, and external components of working voltage measurement;  measuring the PIN IC on DC voltage value and compared with the normal value, which in turn compression failures, identify the damaged components. When measuring, pay attention to the following eight points: (1) multimeter to the internal resistance is large enough, at least, be greater than the measured circuit resistance more than 10 times, so as to avoid larger measurement error. (2) usually refer to the potentiometer to the middle position, if it is a TV set, signal source to a standard color bar signal generator. (3) the table amount or probe to take non-skid steps.  For any moment short-circuit are easily damaged IC.  You can take the following methods to prevent the table from sliding pen: a bicycle valve core set in table tip and long out of table tip about 0.5mm around, this makes the table tip good contact with the test points, and can effectively prevent skidding even run into adjacent points do not short circuit. (4) when measured a PIN voltage does not comply with the normal value should be based on the PIN voltage on IC works have no significant impact, as well as other pin voltage changes, in order to judge the IC.  (5) IC pin voltage will bePeripheral components.  When the peripheral components occurs leakage, short circuit, open circuit or a constant value, or the peripheral circuit connection of a resistance variable potentiometer, potentiometer sliding arm position, will enable pin voltage change. (6) if the PIN voltage IC, generally considered the normal; if IC IC part pin voltage anomalies, the normal value should be from deviation from the maximum service start, check the external components with and without fault, if fault-free, the IC is most likely corrupted.  (7) for dynamic receivers, such as TV, no signal, IC member pin voltage is different.   If it is discovered that the PIN voltage should not change but instead changes, the following signal size and adjustable components of different locations and change but do not change, you can determine the IC is damaged. (8) for a variety of devices, such as a VCR, in different work modes, IC member pin voltage is different. 3. AC voltage measurements in order to master the IC AC signal changes that can be used with dB Jack multimeter on IC AC operating voltage for approximate measurements. Detection multimeter in AC voltage, is inserted into the table amount; for no dB Jack dB Jack multimeter, you will need is a pen thread table 0.1 ~ 0.5 μ F capacitance.   The Act applies to the operating frequency is lower, such as TV IC video zoom level, field scanning circuits, etc. Because of these circuits of natural frequency, waveform, so the measurement data are approximate, only for reference. 4. total current measurement Act is done by detecting IC power total current, to judge the IC is good or bad. Because the vast majority of IC internal for direct coupling, IC damage (such as a pn junction breakdown or open circuit) causes after the level of saturation and closing so that total current change.    So by measuring the total current method can determine the IC. Can also be used to measure power supply pathway of voltage drop in the resistance, Ohm's law to calculate the total current value. The above testing methods, the advantages and disadvantages, in practice it is best to combine a variety of methods, flexible use.

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