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15:46 Mar 9, 2007
This question was closed without grading. Reason: Answer found elsewhere
English to Italian translations [PRO] Tech/Engineering - Mechanics / Mech Engineering / ultrasonic cleaning plant
English term or phrase:front-to-back resistance
La frase esatta è:"Use a ohmmeter and measure the front-to-back resistance of each diode and tyristore (TH3-D1, TH4-D2) in the half controlled bridge rectifier.
Si sta parlando del generatore di ultrasuoni di un impianto di lavaggio ad ultrasuoni.
2. A ratio of parameters used to characterize rectifiers or other devices, in which electrical current, signal strength, resistance, or other parameters, in one direction is compared with that in the opposite direction.
-------------------------------------------------- Note added at 17 days (2007-03-27 09:56:18 GMT) --------------------------------------------------
If a diode has been subjected to excessive voltage or temperature and is suspected of being defective, it can be checked in various ways. The most convenient and quickest way of testing a diode is with an ohmmeter (fig. 1-28). To make the check, simply disconnect one of the diode leads from the circuit wiring, and make resistance measurements across the leads of the diode. The resistance measurements obtained depend upon the test-lead polarity of the ohmmeter; therefore, two measurements must be taken. The first measurement is taken with the test leads connected to either end of the diode and the second measurement is taken with the test leads reversed on the diode. The larger resistance value is assumed to be the reverse (back) resistance of the diode, and the smaller resistance (front) value is assumed to be the forward resistance. Measurement can be made for comparison purposes using another identical-type diode (known to be good) as a standard. Two high-value resistance measurements indicate that the diode is open or has a high forward resistance. Two low-value resistance measurements indicate that the diode is shorted or has a low reverse resistance. A normal set of measurements will show a high resistance in the reverse direction and a low resistance in the forward direction. The diode’s efficiency is determined by how low the forward resistance is compared with the reverse resistance. That is, it is desirable to have as great a ratio (often known as the front-to-back ratio or the back-to-front ratio) as possible between the reverse and forward resistance measurements. However, as a rule of thumb, a small signal diode will have a ratio of several hundred to one, while a power rectifier can operate satisfactorily with a ratio of 10 to 1.
Gian Italy Local time: 11:15 Specializes in field Native speaker of: Italian PRO pts in category: 2464