Look at the electric circuit and answer the questions.

• What elements does this circuit include?
• How are the elements connected?
• Is the value of current the same in all the elements?
• Is the value of voltage different in all the elements?
• Is this circuit a parallel circuit?

Do the following tasks.

Task 1.

Resistance equals 80 ohm, voltage equals 55 volt. How much is the current in the circuit?

Task 2.

Resistance equals 10.5 ohm, current equals 35 ampere. How much is the voltage in the circuit?

Task 3.

Voltage equals 80.7 volt, current equals 120 ampere. How much is the resistance in the circuit?

Task 4.

According to the scheme determine the voltage measurement relative error of resistor R1. Accuracy class of analog voltmeter is 1,5 and accuracy class of digital voltmeter is 0.5.

Task 5.

Determine relative error of the interaction, if Rн=1000 Om and resistance of voltmeter is 1 Mom.

Task 6.

Is this scheme correct? Justify your answer.

Task 7.

Can we use this voltmeter for voltage measurement of resistor R1? If U=50 V, R1=500 Om, R2=30 kOm, R3=10 kOm.

13. Make a short presentation on the topic: ”Voltage measurement”.

14. Form past participle of the following verbs:

To misgive, to stride, to withdraw, to strew, to heave ,to partake, to draw, to cleave, to dwell, to rend, to leave, to smite, to spread, to stride, to upset, to suit.

Read and translate text B.

TEXT B

Digital voltmeter

A digital voltmeter (DVM) attains the required measurement by converting the analog input signal into digital, and, when necessary, by discrete-time processing of the converted values. The measurement result is presented in a digital form that can take the form of a digital front-panel display, or a digital output signal. The digital output signal can be coded as a decimal BCD code, or a binary code.

The main factors that characterize DVMs are speed, automatic operation, and programmability. In particular, they presently offer the best combination of speed and accuracy if compared with other available voltage-measuring instruments. Moreover, the capability of automatic operations and programmability make DVMs very useful in applications where flexibility, high speed and computer controllability are required. A typical application field is therefore that of automatically operated systems.

When a DVM is directly interfaced to a digital signal processing (DSP) system and used to convert the analog input voltage into a sequence of sampled values, it is usually called an analog-to-digital converter (ADC).

DVMs basically differ in the following ways: (1) number of measurement ranges, (2) number of digits, (3) accuracy, (4) speed of reading, and (5) operating principle.

The basic measurement ranges of most DVMs are either 1 V or 10 V. It is however possible, with an appropriate preamplifier stage, to obtain full-scale values as low as 0.1 V. If an appropriate voltage divider is used, it is also possible to obtain full-scale values as high as 1000 V.

If the digital presentation takes the form of a digital front-panel display, the measurement result is presented as a decimal number, with a number of digits that typically ranges from 3 to 6. If the digital representation takes the form of a binary-coded output signal, the number of bits of this representation typically ranges from 8 to 16, though 18-bit ADCs are available.

The accuracy of a DVM is usually correlated to its resolution. Indeed, assigning an uncertainty lower than the 0.1% of the range to a three-digit DVM makes no sense, since this is the displayed resolution of the instrument. Similarly, a poorer accuracy makes the three-digit resolution quite useless.

The speed of a DVM can be as high as 1000 readings per second. When the ADC is considered, the conversion rate is taken into account instead of the speed of reading.

DVMs can be divided into two main operating principle classes: the integrating types and the nonintegratingtypes.

Date: 2016-04-22; view: 937