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Non Profit Joint Stock Company

«Almaty University of Power Engineering and Telecommunications»

Department of Electric Drive and Automation of Industrial Installations

CALCULATION GRAPHIC WORK №2

On discipline Information and Measuring Technologies

Done by: student of group EPEe-16-8

Duisembayeva T.E.

Credit book number: 164155

Checked by:senior lecturer Abdulina Z.V.

Almaty, 2017

Content

Introduction……………………………………………………………………...…3

1.Bridges of direct and alternative current..........……………………………….....4

1.1 Task 1………...…………………………………………………………...4

1.2 Task 2………...…………………………………………………………...5

1.3 Task 3………...…………………………………………………………...6

2.Self-oscillatory mode of a scanning generator…………………………………...7

2.1 Task 1……………………………………………………………………..7

2.2 Task 2……………………………………………………………………..9

2.3 Task 3………………………………...…………………………………...8

Conclusion……………………………………………………………..………….10

Reference…………………………………………………..….………..................11

Introduction

It is difficult to imagine modern systems for automatic control of production processes and telecommunications for voice, data and image transmission, which can be designed and operated without taking the measurements necessary to assess their quality and technical condition.

The main purpose of the computational and graphic work is to consolidate theoretical knowledge and acquire practical skills for measuring the parameters of electrical signals with the required accuracy. To do this, it is necessary to make the right choice of the measuring device, the measurement method for eliminating additive and multiplicative errors, to be able to use not only traditional devices (analog and digital), but also virtual, computerized complexes, for example, the LabVIEW system.

CGW No. 2 is devoted to the study of methods of measuring resistances with the help of bridges of direct and alternating currents, as well as studying the operation of the oscilloscope in various modes when measuring signal parameters.

1.1Bridges of direct and alternative currents

Task 1

In couple of wires of a multicore connection cable there was a breakdown of isolation in some point (fig. 3.1). The cable is executed from a copper wire with the section of 1,5 mm².

It is necessary to locate damages of the line by means of the express device – Murray Bridge.

Figure 3.1 – Metallic circuit of a multicore cable

Solution:

S = 1,5 mm² = 1,5 ∙ 10^-6m²

ρ = 1,75 ∙ 10^-8 Ohm∙m

L = 2km = 2∙ 10³m

R₁ = 85Оhm

R₂ = 995Оhm

= 23,33Оhm

= 3,67Оhm

= 314,6m

Task 2

The alternating-current balanced bridge is set. Parameters of three shoulders and alternating-current frequency of the power supply of the bridge are known.

It is required to determine the capacity and a loss angle of the studied C1 condenser (see the figure 2). Variants of tasks are chosen according to table 2.

Solution:

R₂ = 2300 Ohm

R₁ = 107.3 Ohm

C₀ = 0.05 mcF

r₀ = 75 Ohm

f = 400 Hz

Equilibrium condition of the bridge is

(r_x + 1/jωc₁) · R₂ = (r₀ + 1/jωc₀) · R₁

where r_x, r₀ – the active components of arms of bridge;

jωc₁, jωc₀ – reactive components of arms of bridge.

Then:

С₁ = С₀R₂/R₁; r₁ = r0R₁/R₂;

tgδ₁ = r₁/XС₁ = ωr₁С₁ = ωr₀С₀.

Task 3

The alternating-current balanced bridge is set (see the figure 4). Parameters of three shoulders are specified in table 3, the alternating-current frequency of the power supply is equal to f = 100 Hz and the capacity of the model condenserC₀ = 0,1mcF.

It is required to define inductance and the fissile coil resistance and also its good quality. Variants of tasks are chosen according to table 3

Solution:

f = 100 Hz

C₀ = 0,1mcF

R₂ = 97 Ohm

R₃ = 104 Ohm

r₀ = 1.4 kOhm

Equilibrium of the bridge comes under a condition

Z₁Z₀ = R₂R₃

Where Z₁ = r₁ + jωL₁;

Z₀ = r₀/ (1 + jωС₀r₀)

After transformation we will receive

r₁r₀ + jωL₁r₀ = R₂R₃ + jωС₀r₀R₂R₃.

Then

r₁ = R₂R₃/r₀; L₁ = C₀R₂R₃.

Quality factor off the coil

Q = ωL₁/r₁ = ωC₀r₀

Theme 2. Measurement of parameters of signals by means of EO

2.1 Self-oscillatory mode of a scanning generator

Task1

On the main input U the electronic oscilloscope (EO) has a sinusoidal voltage U_y = U_my ∙ sinω_yt. The scan generator (SR) operates continuously and generates a sawtooth signal U_p = at with frequency f_p = 25Гц.

It is required to determine the number of images of the sinusoid of the input signal on the EO screen.

Figure 2.1 - Timing diagram of the input signal

Solution:

U_my = 5V

U_mp = 10V

f_y = 250 Hz

U_y=U_my∙sinω_yt

ω_y=2πf_y =6,28∙250=1570rad/s

U_y =5 ∙ sin1570t

T_p == 0.04s

T_p = =>n = T_p ∙ f_y = 0.04∙250 =10s

2.2 Frequency measurement with EO

Task 2

On an entrance of EO rectangular impulses arrive, GR works in the waiting mode. Are set: time of a delay of tz and development of Tr (see the figure 2).

It is required to determine the greatest possible duration of ti of an entrance impulse at the set GR parameters. The image of an impulse on the EO screen will be full if time of development of the horizontal line after the termination of an impulse is not less 0,1tz. Variants of tasks are chosen according to table 2.

Figure 2 – The chart of work of GR in the waiting mode

Solution:

t₃=30mcs

T_p=0.3ms

t_u=T_p-t₃-0.1t₃=0.310^-3-3010^-6-0.13010^-6=0.27310^-3s=0.273ms

Task 3

A sinusoidal signal with an unknown frequency f_x is applied to the vertical input (input Y) of the electronic oscilloscope EO. On the horizontal input (input X) a signal is sent from the sample sinusoidal signal generator (SSS) with frequency f_o. At some frequency ratio f_х/f₀ , a stationary figure of Lissajous is obtained on the screen (Table 4.3).

It is required to determine the unknown frequency f_x and the measurement result. If the relative error of the frequency of the HSF is equal to δ_отн.

Solution:

f₀ = 100Hz

δ_отн = 2 %

N_г = 2, N_в = 6

Conclusion

I studied the methods of measuring resistances with the help of bridges of direct and alternating currents, and also studied the work of the oscilloscope in various modes when measuring the signal parameters.

Reference

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2. Боридько С.И., Дементьев Н.В. Метрология и электрорадиоизмерения втелекоммуникационных системах. – М.: Горячая линия–Телеком, 2007. – 374 с.

3. Воротников С.А. Информационные устройства робототехнических систем. – М.: Изд – во МГТУ им. Н.Э. Баумана, 2005. – 384 с.

4. Назаров Н.Г. Метрология. Основные понятия и математические модели. – М.: Высшая школа, 2002.- 348 с.

5. Раннев Г.Г. Методы и средства измерения. – М.: Изд. Цент «Академия», 2006. – 336.