Measurement of electrical quantities

The purpose of the work. To get acquaintance with work principles, classification and basic metrological characteristics of electric measuring instruments. To determine resistance using an ammeter and a voltmeter

Devices of and accessories Electrical scheme for resistance determination

Task 1. Get acquaintance with the electric measuring instruments

1.1. Get acquaintance with the devices and put down characteristics of ammeter and voltmeter into tables 3 and 4.

1.2. Calculate the scale factor for all measurement ranges of the electrical devices.

Enter the results into table 1; 2.

1.3. Determine measurements absolute error using the accuracy class and measurement range of electrical devices according to the formulas:

Enter the results into table 1, 2.

Table 1

Ammeter	Measurement range Imax, A	Amount of pitches N, pitch.	Scale factor C, A/pitch	Accuracy class %	Absolute error I, A	Ammeter resistance RA, 

Table 2

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

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

Scale part	Current, І		Voltage, U		Rx, Ω	R, %	Rx, Ω	І, %	U, %
	Pitches	А	Pitches	V
Last third
Medial part
Initial third

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 U and I 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