Measurement of a constant and alternating voltage

In radio engineering the potential difference between two points is called as tension. The term «падение напряжения» is sometimes applied;. The device for measurement of tension is called as the voltmeter. As a rule, on a tester the mode of the voltmeter is designated by DCV and ACV that is deciphered as constant tension and an alternating voltage respectively. Sometimes these modes are designated as V and V ~. The voltmeter is connected by in parallel to a measured site of a chain, that is if we have to measure power failure on the resistor, contacts of a tester are connected by the ends of this resistor without a rupture of a chain. As it is known from a physics course, at parallel connection of conductors tension on them is identical, and indications of a tester which as we remember, can measure only myself, will be almost equal to tension on a measured site of a chain. But necessary conditions are carried out not always. If indications not such, predictably, remember that resistance of a tester in a mode of the voltmeter is very great and makes about 10 megohms. Therefore at tension measurement on resistance, comparable already with 1 megohm, the tester will give the underestimated evidences. But in amateur radio engineering such resistance meet very seldom. Tension measurement between two untied points (for example, tension in the household socket) is possible in case the source of tension can give out a current considerably bigger, than U/10 megohm, where to U - measured tension. For the majority of sources it is carried out, but, say, at creation of high-voltage low-power sources it is necessary to remember it.

There is one more problem, and it is connected with measurement of an alternating voltage. The diodes used for its straightening in a tester, have considerable power failure and low boundary frequency. Therefore at measurement of variable tension in 1-3 In a tester will issue the underestimated indications. It should be remembered. The tester also is not able to measure high-frequency tension and begins «врать» (to underestimate real indications) already from frequencies in some hundred kilohertzes.