Saturday, January 1, 2011

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

Use a pointer multimeter to distinguish optocoupler. The author of four foot type PC817 opto coupler to illustrate its discriminant method.
In optocoupler, contains a light emitting diode and a phototransistor.
1. determine the PIN light emitting diode. Use MF30 multimeter R × 1 k Ω, on any of the four just feet feet for forward and backward measurement, if you have a table pin index is infinite, but the table amount of swap, 30 k Ω after around resistance values, the black table pens made of tube feet is the cathode light emitting diode, red table pens made of tube feet for light emitting diode anode.
2. determine the phototransistor of collector and emitter. In optocoupler phototransistor NPN-normally, and ordinary NPN silicon transistor has many similarities. Multimeter R × 10 k Ω, remaining on PC817 feet. If you have a resistance to infinity, but exchange table pen after 250 k Ω or resistance values, then this black table amount received the PIN is the optical transistor emitter, red table amount received the PIN for the photo-transistor collector.
So far, four feet optical coupling pin arrangement PC817 has completely OK, as shown in the drawings. As regards the number of feet of optical coupling tube pin arrangement, you should first of all light-emitting diode, pin discriminant and then determine the corresponding phototransistor PIN. Multimeter testing transformer power only a multimeter is not enough, you can find several motorcycle lamp, according to the output voltage of the transformer, the transformer series lamp access output multimeter measuring the output terminal voltage, transformer output go parallel output voltage bulb, found significantly lower in many cases, stop continue parallel bulb, remember the voltage value. Then use the current measured at multimeter, remember current value. Voltage value × current value = basic digital multimeter and a rated power of the pros and cons of needle and digital multimeter has advantages and disadvantages. Pointer multimeter is an average-instruments-it has intuitive reading indicates that the image (usually read numeric and pointer swing angle are closely related, so it is very intuitive). Digital multimeter is instantaneous access style instruments-it uses 0.3 seconds in a time-like to display the measurement result sometimes each sampling results very similar-but is not exactly the same as the results for read-just not as convenient. analog multimeter pointer general internal no amplifiers-so the internal resistance is smaller. for example, type MF-10 DC voltage sensitivity of 100 kilohms/Volt. This is prizes the .MF-500-DC voltage sensitivity of 20 thousand euro/Volt. digital multimeter for internal uses operational amplifier circuit. internal resistance could be very large. 1M often in Europe or greater. (That is, you can get a higher sensitivity). This makes the device under test circuit can be smaller. measurement accuracy is high. Digital multimeter because the internal resistance is smaller, and the use of discrete components constitute the shunt Volt circuit. therefore frequency characteristic is heterogeneous (in terms of relative digital). While the frequency characteristics of analog multimeter relatively better.

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