Table 2

Voltmeter	Measurement range Umax, V	Amount of pitches N, pitch.	Scale factor C, V/pitch	Accuracy class %	Absolute error DU, V	Voltmeter resistance RV, W

Task 2. Make an electric circuit for unknown resistance R determination

2.1. Make an electric circuit as shown in figure.

2.2. Choose measurement range of ammeter and voltmeter in such a way that their pointers deviate synchronously.

2.3. Check up the electrical circuit and lock the circle by the key K.

2.4. Move the rheostat sliding contact in such position, where the pointers of the devices are in the third part of their scales. Enter amount of pitches according to voltmeter and ammeter scales into table 3.

2.5. Move the rheostat sliding contact in such position, where the pointers of the devices are in medial part of their scales. Enter pitches amount according to voltmeter and ammeter scales into table 3.

2.6. Move the rheostat sliding contact in such position, where the pointers of the devices are in initial part of their scales. Enter amount of pitches according to voltmeter and ammeter scales into table 5.

2.7. Unlock the circle by the key K.

Table 3

Task 3. Calculation of the value of unknown resistance R_x and the measurements error determination

3.1. Using data from table 1–3, calculate the value of unknown resistance according to the formula:

Enter the results into table 3.

3.2. Calculate the absolute and the fractional errors of R_x determination according to the formulas:

where DU and DI is absolute errors of voltmeter and ammeter measurements (see tables 1–2):

Enter the results into table 3.

3.3. Determine the fractional errors for each measured value of current and voltage according to the formulas:

Conclusions

The data of laboratory work fulfillment

Pass mark Signature

Mark of laboratory work defending Signature

questions to be admitted for doing laboratory work and its defending

1. What measuring devices do you know?

2. What is permissible error limit of electric measuring instruments?

3. What metrological characteristics of measuring devices do you know?

4. Give the definition of accuracy class of measuring devices.

5. What is sensitiveness and scale factor of measuring device?

6. How can absolute and fractional errors of measurements be calculated?

7. What are absolute and fractional errors of current and voltage measurements determined?

8. Does absolute error of current and voltage measurement depend on the value of the measured quantities?

9. How are ammeter and voltmeter measurements ranges chosen?

10. Draw the scheme of the experimental electrical circuit.

11. Deduce the formula for the calculation of unknown resistance R_x.

12. Deduce the formula for the calculation of absolute error of unknown resistance R_x.

13. How can the measurement range of ammeter and voltmeter be changed?

14. Deduce the formula for the shunt resistance calculation.

15. Deduce the formula for the voltmeter additional resistance calculation

LABORATORY WORK

Date: 2015-01-12; view: 893