Monday, January 3, 2011

【 Weak current College 】 universal table usage 】

A pointer to the tables and figures, and tables of selection:

1, pointer poor table reading accuracy, but the process of the pointer swing, swing more intuitive speed ranges may sometimes compare objectively reflects the measured size (such as measuring TV data bus (SDL) to transmit data at a slight jitter); digital table reading intuitive, but the numbers change process looks cluttered, is not easy to watch.

2, pointer table in general have two batteries, a low voltage 1.5V, one is a high voltage of 9 v or 15V, the black table pen relative red table is positive-sum. A commonly used digital table or 9V battery 6V. In the resistance, pointer table pen output current relative numeric tables to a much larger, with R × 1 Ω stalls can make loud speakers "da" sound, with R × 10 k Ω stalls even light-emitting diode (LED).

3, in the voltage rail that pointer table is the table of relative digital internal resistance is smaller,-measuring accuracy compared to the poor. Some high voltage micro-current occasions even unable to measure accurately, because of its resistance to impact measured circuits (for example, in measuring TV picture tube acceleration level voltage measurement values than the actual value is much lower). Digital voltage rail internal resistance of the table, at least in megohm-level, the impact test circuit is small. But very high output impedance makes it vulnerable to the effects of induced voltage, and in some relatively strong electromagnetic interference situations measured data can be virtual.

4. in short, in relatively large current and high voltage analog circuit measurement applicable pointer table, such as television sets, audio amplifier. In low-voltage low-current digital circuit measurement applicable digital table, such as BP machine, mobile phone, etc. Is not absolute, according to the situation to select pointer tables and figures on the table.

2. measurement techniques (if not described, using a pointer table):

1. measuring speakers, headphones, moving coil microphone: used R × 1 Ω, any table pen pick end, another table for the pen at the other end, normal dianchu issue crisp sound of "click" sound. If not, then is the coil, if the noise is small and sharp, is a Polish circle, also cannot be used.

2. capacitance: resistance, according to the capacity to select the appropriate range, and note the measurements for Electrolytic Capacitor black table pen to add capacity cathode. ①, estimation of microwave-level capacity size: experience or reference the same capacity of standard capacitors, according to the most significant swing of a pointer to the judgment. The reference of capacitance do not have to withstand voltage too, as long as the same capacity, such as estimating a 100 μ F/250 v capacitors are available in a 100 μ F/25 v capacitors to reference, as long as they like the most drastic swing the pointer, you can conclude that capacity. ②, estimating rind-capacitor size: want to use R × 10 k Ω stalls, but can only be measured more than capacitor 1000pF. To 1000pF or slightly larger capacitance, as long as the table pin slightly swing, you can view capacity enough. ③, whether leakage capacitance: more than a thousand micro-method, you can use the capacitance R × 10 Ω stalls to fast charge, and a preliminary estimation of capacitance, and then change to the R × 1 k Ω stalls dating for a while, then continued the pointer should not return, and should stop at or very close to ∞, otherwise there is a leakage phenomenon. On some dozens of micro method the following timing or oscillation capacitor (such as TV switching power supply's oscillation capacitors), on its leakage characteristics with the very high, the slightest leakage cannot be used when available in R × 1 k Ω stalls after filling out electric switch R × 10 k Ω stalls continue to measure, the same hands should stop at ∞ Department and not return.

3, in the road test, Zener diode, triode tube is good or bad: as the actual circuit, transistor bias resistor or diodes, Zener tube peripheral resistance are relatively large, mostly in the hundreds of thousands more than this, Omron, we can use multimeter R × 10 Ω or R × 1 Ω stalls to road measuring pn junction is good or bad. Measurement in the road, with R × 10 Ω stalls dating PN should have a clear forward and backward properties (if the difference between forward and reverse resistance are less obvious, you can use the R × 1 Ω stalls to measurement), the General positive resistance in R × 10 Ω rail measuring table pin should indicate in 200 Ω at R × 1 Ω stall timing table pin should indicate 30 Ω or so (depending on the phenotype may slightly). If the measurement results to the resistance is too big or too small, reverse resistance, have shown that there is a problem with the pn junction, this tube is also a problem. This method is particularly effective for repair, you can very quickly find broken pipe, even measure has not been completely broken but the characteristics of the deterioration of pipes. For example, when you use small resistance measurement of a pn junction stalls to the resistance is too large, if you put it down to the commonly used welding R × 1 k Ω stalls then measured, may be good, in fact, the pipe character has become broken, not working correctly or is not stable.

4. measuring resistance: it is important to select the right range, when the pointer indicates that 1/3 to 2/3 full time measurement accuracy highest, most accurate readings. Notably, in measuring with R×10k resistance stalls megohm-great resistance, not the fingers in the resistance ends, so the human resistance causes the measurement result is small.

5. measure Zener diode: we usually used voltage tube voltage value is generally greater than 1.5V, and pointer table R×1k following resistance gear is used in battery-powered 1.5V, such that the electrical resistance of R×1k following stalls measurement voltage tube is like measuring the diode, has full one-way conductivity. But the pointer table R×10k stalls is a 9V battery or 15V, using measuring voltage value is less than R×10k 9V or 15V voltage tube, reverse resistance would not be ∞, but have a certain resistance, but this resistance or much higher voltage tubes forward resistance. So, we can estimate the regulator hose initially. However, good voltage tube also has a precise voltage value estimation of the amateur: how the condition of the voltage value? not difficult, go find a pointer to the table. First a table placed R×10k stalls, its black and red table pens respectively inVoltage tube cathode and anode, analog out voltage tube working status, and then take another table into voltage rail V×10V or V×50V (according to the voltage value), the red and black table amount respectively to have just one splice table of black, red, then on the table amount measured voltage value is essentially the voltage tube voltage values. "Basically," because the first table on voltage tube bias current relatively normal use of the bias current slightly smaller, so measured voltage value is slightly larger, but the basic difference is not significant. This method is only available to estimating the voltage value is less than pointer table-voltage battery voltage regulators. If the voltage tube voltage value is too high, you can only use the power of methods to measure the (so that we in the selection pointer table, choose the high-voltage battery voltage 15v than some of the more suitable 9V).

6. measuring triode: usually we use R × 1 k Ω stalls, NPN or PNP pipe pipe, whether it is a low power, medium power, high-power tube, measuring their cb be knot knot should be rendered exactly the same with diode one-way conductivity, reverse the resistance infinity to the resistance around about 10K. To further estimate the pipe character is good or bad, if necessary, should transform resistance stalls for several measurements, methods are: reset R × 10 Ω stalls dating pn junction is Wizard-resistance are around in about 200 Ω; reset R × 1 Ω stalls dating pn junction is Wizard-resistance is approximately 30 Ω, (the above is 47-table of the measured data to other model table probably slightly more tests a few good tube to sum up, be aware of) if the reading is much too much, you can determine the characteristics of the pipe. You can also place the table R × 10 k Ω and then measuring, pressure and then lower the pipe (basically the transistor voltage are 30V above), the cb-reverse resistance should be, but its infinity of reverse some resistance may, table needle deflection slightly (generally not exceeding the full range of 1/3, under the pressure of the pipe is different). Similarly, the use R × 10 k Ω stalls dating between ec (NPN) or ce (on PNP tube) of resistance, the hands may be slightly biased, but this does not mean that the pipe is bad. But using R × 1 k Ω following stalls dating ce or resistance between ec, table headers indicate is infinite, the tube is a problem. You should note that these measurements are for Silicon tubes, tubes for GE. But now it is very rare in Germanium tube. In addition, the "reverse" is a pn junction, NPN and PNP pipe direction is different.

Now the most common of the transistor is shrink-wrapped, how to accurately judge the transistor's three pin which is b, c, b e? triode very easily measured, but how do you tell which is which is e c? here recommend three ways: the first method: measurement of transistor hFE for Jack's first gauge pointer table b, the transistor randomly inserted into the Jack on the go (of course you can plug the b is extremely accurate), have your hFE value, then the tube upside down and then test again, the measured value larger hFE once the PIN insertion position is correct. The second method: measurement of hFE-Jack tables, or pipe is too large to facilitate insertion Jack, you can use this method: NPN, first measure b (NPN or PNP pipe is and its b feet are easy to detect, isn't it?), a table placed R × 1 k Ω in the red table amount received extremely hypothetical e (note taking red table pen hand not encountered table tip or PIN), the black table amount received extremely hypothetical c, while finger squeeze table tip and the PIN, will take up the pipe, use your tongue lick b, see header pointer should be deflected if you have received the table amount is correct, the pointer deflection would be greater, if something wrong, pointer deflection is smaller, the difference is obvious. From here you can determine the tubes of the c, e. On PNP tube, to move the black table amount received extremely hypothetical e (hand not to encounter the pen or PIN), red hypotheses of the table amount received, while c extreme fingers live table tip and the PIN, and then use the tongue lick b, if the table amount received correctly, the table header pointer deflection is relatively large. Of course measurement table pen to swap out a comparative measure twice, before the final judgment readings. This method applies to all appearance of triode, facilitates practical. Deflection of the needle under the table, you can estimate the capacity of amplification tubes, of course, this is the experience. The third approach: first determine pipe of NPN or PNP type and b, the table over R × 10 k Ω stalls, NPN, black table amount received e-pole, red table amount received when the table c is likely to have a needle deflection on PNP tube, black table amount received extremely red table c, e very received the pen, the hands may have a certain amount of deflection, which in turn will not be a deflection. From here you can determine the transistor of c, e. But for high pressure pipe, this method is not applicable.

For common import model of power, the plastic tube c very basic is in the middle (I haven't seen before b in the middle). Medium and small power possession b most probably in the middle. For example, the commonly used 9014 triode and series of other models 2N5401 transistor, 2SC1815, etc, transistor, its 2N5551 b very in the middle. Of course they also have c pole in the middle. So when the repair replace triode, especially these Audion, not to install directly on as is, we must first look at logging.

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