“Oh that You would bless me with Your blessing, enlarge my borders, and Your hand would be with me, protecting me from evil, so that I would not grieve!.. And God sent down to him what he asked” (1 Chron. 4:10 ).

We are familiar with these words and this amazing story through the book “The Prayer of Jabez.” You remember: pain, loneliness, rejection and doom. This is not just the fate and experiences of this biblical character, but, look closely, this is the fate of many of our compatriots. Sometimes it even seems that this is the lot of evangelical believers and the evangelical church in our country. And at such moments, Jabez is especially remembered, inspiring us to believe, dream, and experience a similar story in our personal lives, to pray and ask for expansion, spreading the boundaries of missionary service, according to the plan and blessing of God, with the assistance of His supporting hand, protecting us from evil, so that we do not grieve.

Like us, looking around the vast expanses of Russia, Jesus looked with his disciples at their native Palestinian fields and said: “Pray the Lord of the harvest to send out laborers into His harvest” (Matthew 9:38). He first invited them to pray for the expansion of God's work, and then, as a result of their heartfelt participation in this prayer and as a consequence of the expansion of their vision, He sent them out on mission in twos.

Before we talk about territorial expansion and expansion of influence, we need to talk about developing our missionary vision and expanding the boundaries of our hearts. The Apostle Paul states to believers: “You are not crowded with us; but your hearts are cramped... you also will be enlarged” (2 Cor. 6:12). We need to enlarge our hearts for mission again and again, to renew and sanctify our intentions. We need pure motives love and compassion for the individual sinner and the perishing crowds, contrition and constant pain in the heart for our compatriots near and far, as well as expanding the horizons of acceptance different people and participation in their special destinies.

Thus, first - prayerful cooperation with God, then - a change in our hearts and our inner limits, after which the boundaries of our participation, service and influence expand.

How important this prayerful upsurge is for us now, this cry and cry to the sky: “Oh, that You would bless me with Your blessing and expand my borders!” How we need these intercessors, who, as intercessors for our Russian lands, cry out and cry before the Lord: “O God, the laborers have gone out into the ripe fields.” Let this representative prayer for the people of Christ rush to God: “Spread and enlarge the hearts of Your children, O Lord!” Indeed, only a special blessing from God, intended for our days, can expand the boundaries of His Kingdom in our country. This renewal will change and expand our understanding of modern missionary service, new ways to reach people with salvation in Christ Jesus, planting new churches and multiplying the gospel church in the country and further abroad.

“Oh that You would bless me with Your blessing, enlarge my borders.” This is a prayer for the endless expanses of central Russia, and not only for central Russia, where in many regions there are only three to five evangelical churches. There are areas where there are only 200–300 Christians. And again I remember: Jabez – pain, loneliness, doom and rejection. But there is a prayer and a dream, an answer and a special blessing.

When I think about cities with over a million people, I remember with joy that in modern Russia Our partners have experienced the amazing blessing of church multiplication in Yakutia. This did not happen somewhere abroad and not in some ancient times - today, through the same missionaries, from our own churches, more than 60 churches were formed within 15 years. At the same time, exactly one million people live in Yakutia. If the same thing happened in Moscow, then more than 1000 new churches would have been founded there today. Thank God for new churches in Yakutia! But the question remains: “Lord, is it possible for so many churches or more to be established in cities with a population of one million? Oh, that You would bless me with Your blessing and expand my borders!”

We can pray for a special blessing for our megacities and million-plus cities. We can dare in prayer that the Lord will send workers to these fields. This is possible for God, He is doing it today in our Russia. We need a special blessing, a wonderful time of visitation for our large empty cities and an enlargement of our heart boundaries.

Semyon Borodin,
Bishop of the EHMC for mission in Central Russia,
Senior Pastor of the “Good News” Church, Moscow

Extending the measurement limits of the voltmeter is achieved by connecting an additional resistance in series with the existing device (Fig. 5).

According to Fig. 5 we have:
. From here we obtain an expression for determining the value of additional resistance:
(6), where U etc - the maximum voltage for which it is determined R ext , I etc - deflection current of the device needle, r vn - internal resistance of the device. Usually additional resistance R ext It is made from magnesium or constantan wire, as well as from graphite and metallized resistances.

2. Expanding the measurement limits of ammeters

DIRECT CURRENT.

To expand the measurement limits of DC ammeters, shunts are used. A shunt is a resistance that is connected parallel to the frame of the measuring device (Fig. 6). The shunt removes part of the total current I about through itself and thereby reduces the current flowing through the frame of the device.

WITH According to Fig. 6 we have:
, or
.

From here, after transformation, we obtain the ratio by which the shunt resistance is determined:

(7),

Where r vn - resistance of the device frame,
, I about - the amount of current that needs to be measured, I vn- current of full deflection of the instrument needle.

3. Expanding the measurement limits of ammeters

ALTERNATING CURRENT.

To measure large alternating currents, measuring current transformers are used, which not only make it possible to expand the measurement limits of ammeters, but also allow them to be well isolated from high voltage circuits, which is important for safety reasons. The current transformer consists (Fig. 7) of two primary windings, connected to the network and designated by letters L 1 And L 2 (L 1,2 - switches on towards the generator), and the secondary, designated by the letters U 1 And U 2 and connects to an ammeter.

Current transformers are made portable, as well as with a detachable core, the so-called current clamps, which are used to measure current without breaking the circuit, for example, on power lines of 220-380 V.

EXPANDING LIMITS

ALTERNATING CURRENT VOLTMETER MEASUREMENTS.

D To expand the measurement limits of AC voltmeters, voltage measuring transformers are used (Fig. 8).

The primary winding of the voltage transformer is connected to the high voltage network, i.e. controlled circuit. A voltmeter is connected to the secondary winding of the voltage transformer, as well as parallel coils of a wattmeter, phase meter and other measuring instruments.

EXERCISE 1

R calculate using formula (6) and select the nominal additional resistances for the voltmeter at the resistance store V 2 with measurement ranges of 30 and 160V in order to expand its measurement limits to 220V.

Assemble the circuit according to Fig. 9, where V 1 -control voltmeter 300V, a V 2 - voltmeter being tested. As R ext a resistance store is used.

By changing the input voltage, take 10-15 instrument readings V 1 And V 2 , write them down in table form and build a graph
. Plot the values ​​along the abscissa axis V 1 , and along the ordinate axis V 2 .

EXERCISE 3.

WITH
assemble the circuit according to the diagram in Fig. 10. Ammeter A 1 designed for 10A, and A 2 up to 5A. Changing the current using a rheostat R make 10-15 measurements, write them down in table form and build a dependence graph

EXERCISE 4.

Connect the voltmeter to the measuring transformer according to Fig. 11, take measurements and write them down.

CONTROL QUESTIONS.

1. Independently study the design of magnetoelectric system devices. Basic equation of the scale. Advantages and disadvantages of ME system devices.

2.Explain the structure and principle of operation of devices of electromagnetic and electrodynamic systems.

Is it possible to use a magnetic shunt to influence the character of the scale and why?

Will the electrodynamic constant of the device change if it is used not as an ammeter, but as a voltmeter?

5. Is it possible to influence the nature of the scale by changing the counteracting moment?

6. What are instrument transformers used for?

Is it possible to measure DC voltage with an electromagnetic system device?

Electrical engineering.

^ To measure grounding resistance, instruments are used that use one of the following methods:
- ammeter-voltmeter method;
- compensation method;
- bridge method.

Ammeter-voltmeter method.

Compensation method.

Various devices and circuits based on the so-called compensation method for measuring grounding have become widespread.
When measuring using this method, in addition to the main current circuit in the ground, another circuit is created - on a special calibrated resistance. In this case, the circuit is designed in such a way that the same current flows through the calibrated resistance as in the ground. By changing the value of the calibrated resistance, it is possible to achieve such a situation that the voltage drop across this pre-known calibrated resistance will be the same as in the area where the current flows in the ground.

Bridge method.

The bridge method, as its name suggests, uses a linear AC bridge for measurement purposes. Three measurements are made: with the first, the grounding switch - auxiliary electrode circuit is included in the measuring arm of the bridge, with the second - the grounding switch - probe circuit, and with the third - the probe - auxiliary electrode circuit.
This method is inconvenient because it requires three measurements and is not accurate enough. Stray currents in this case have a significant impact, and sometimes even make measurements impossible.

Of the methods described, the most accurate is the ammeter-voltmeter method. If you have good and correctly selected instruments and with correctly conducted experiments, the ammeter-voltmeter method is the best for making critical measurements. Using this method, it is possible to obtain with sufficient accuracy a picture of the change in potential along the surface of the earth near the ground electrode.

^ 49. Methods and means of measuring power.

There are instantaneous, average and pulsed powers of electric current.

Instantaneous power is determined by the expression: p=u*i, where u and i are the instantaneous values ​​of voltage and current in the circuit.

^ Average power P is equal to the average value of instantaneous power over a time equal to the oscillation period,

where T is the period of voltage or current.

^ Pulse power defined as the average power during the action of a voltage or current pulse

where tn is the duration of the voltage or current pulse.

In DC circuits, power is calculated using the formulas

where U and I are the value of constant voltage and current, R is the circuit resistance.

In sinusoidal current circuits, average active, reactive and apparent powers are distinguished, which are calculated using the formulas

where U and I are the effective values ​​of voltage and current in the circuit, R, X and Z are the active, reactive and total resistance of the circuit, respectively: - phase shift.

Distinguish straight And indirect power measurement methods.

Indirect The electrical method of measuring power is based on the use of an ammeter and a voltmeter. Two possible schemes for measuring power using an ammeter and a voltmeter are shown in Fig. 1.a and b.

Fig.1

for the diagram in Fig. 1,a or

^ Direct electrical method Power measurements are based on the use of electrodynamic, ferrodynamic or electronic wattmeters. Connection diagrams for electrodynamic and ferrodynamic wattmeters are shown in Fig. 2. The diagram shown in Fig. 2, a. is similar to connecting an ammeter and voltmeter according to the diagram in Fig. 1, a. The diagram shown in Fig. 2, b. is similar to connecting an ammeter and voltmeter according to the diagram in Fig. 1, b.

The equation of the wattmeter scale without taking into account the errors introduced by the windings has the form

where is the instrument reading, k. is the proportionality coefficient.

Due to the fact that the wattmeter coils have resistance and inductance, an additional error appears in the device readings.

When taking into account the resistance Rv and inductance Lv of the wattmeter voltage coil, an additional angular error appears

where =arctg(Lv/Rv) is the additional phase shift introduced by the wattmeter winding.

^ 50. Measurement of active and reactive power in three-phase circuits.

Active power.

One Wattmeter Method.

Method of two wattmeters.

Three wattmeter method.

Reactive power.

One Wattmeter Method.

Method of two wattmeters.

Three wattmeter method.

^ 51.Power measurement using the voltmeter-ammeter method.

Ammeter-voltmeter method is based on the use of the ratio R=U/I, known from the electrical engineering course, which is a mathematical expression of Ohm’s law. In the formula, R is the resistance of the section of the electrical circuit in which, when current I flows, a voltage drop U occurs. To determine the resistance of the ground electrode, it is necessary to pass a certain current through it and measure the voltage drop in the spreading area. After this, make a simple calculation using the formula.
This method of measuring ground resistance has the following disadvantages:
a) It is necessary to use two measuring instruments simultaneously, and then make calculations.
b) In order to obtain fairly accurate measurement results, you need a source of fairly significant current (tens of amperes) with good stabilization to ensure the ability to take readings from two instruments: an ammeter and a voltmeter.
c) A large current can be a source of additional error, since with a high density of alternating current, the total resistance of steel conductors increases compared to the resistance of the same conductors to direct current.
d) The voltmeter must have a sufficiently large internal resistance.
e) Stray alternating and direct currents in the ground can introduce additional and sometimes significant errors in measurements.

Two possible schemes for measuring power using an ammeter and a voltmeter are shown in Fig. 1.a and b.

For the circuit shown in Fig. 1, a. calculated power value

differs from the power consumed by the load by the amount of power Рv = UаIv consumed by the voltmeter.

For the circuit shown in Fig. 1b, calculated value of power consumed by the load,

differs from the power consumed by the load by the amount of power PA = UaIn consumed by the ammeter.

When measuring power in AC circuits, formulas can only be used with a resistive load, i.e. at cos=1. With a reactive load, the calculation results in the total power. To eliminate errors caused by: connecting measuring instruments, corrections are introduced into the calculation results:

for the diagram in Fig. 1,a or

for the diagram in Fig. 1.b, where Rv is the resistance of the voltmeter, and Ra is the resistance of the ammeter.

^ 52. Expanding the measurement limits of wattmeters.

Extending the measurement limits of wattmeters for current and voltage is achieved using measuring transformers.

Extension of the voltage measurement limits of wattmeters is carried out using additional manganin resistances connected in series with the moving coil.

Extension of the measurement limits of wattmeters for current and voltage is carried out using current and voltage measuring transformers

To expand the measurement limits of wattmeters, their current coils are connected to the circuit using shunts or measuring current transformers, and the voltage coils are connected through additional resistors or measuring voltage transformers.

^ 53. History of standardization.

It can be assumed that hunters who used bows and arrows were among the first to feel the need for standardization, back in the days of the primitive communal system. Indeed, they quickly discovered that in order to accurately hit the target it was necessary to use arrows of a certain length with tips of a certain size and weight. The use of poles of the same length in housing construction should also be considered a prototype of standardization. After the invention of the wheel, the need to use wheels of standard sizes became obvious. Another example of standardization is the use of coins of the same size, shape and weight.

IN Ancient Rome standard pipes were used to make water pipes. Also in ancient Egypt During construction, bricks of a constant “standard” size were used, while special officials were responsible for controlling the size of the bricks. Remarkable monuments of Greek architecture - famous temples, their columns and porticos are assembled from a relatively small number of “standard” parts. The ancient Romans applied the principles of standardization in the construction of water pipes - the pipes of these water pipes were of the same constant size.

In the Middle Ages, with the development of crafts, standardization methods began to be used more and more often. Thus, uniform dimensions for the width of fabrics, a uniform number of threads in its base, and even uniform requirements for raw materials used in weaving were established.

In 1785, the French engineer Leblanc produced a batch of gun locks - 50 pieces, and each of these locks had an important quality - interchangeability; it could be used in any of the guns without preliminary adjustment.

Elements of national standardization have appeared in various countries, for example:

in 1846, the railway gauge and coupling devices for wagons were unified in Germany;

in 1869, a reference book containing the dimensions of standard profiles of rolled iron was first published there;

in 1870, standard brick sizes were established in a number of European countries;

in 1891, the standard Whitworth thread (with inch dimensions) was introduced in England and then in other countries, which was subsequently replaced in most countries by metric threads.

These first results of national and international standardization were of great practical importance for the development of productive forces. However, these were only the first steps.

The increased militarization of many countries at the beginning of the twentieth century required the production large quantity weapons, subject to mandatory observance of the principle of interchangeability; this problem could only be solved through standardization. It is therefore not surprising that several national standards organizations were founded during and immediately after the First World War, for example in Holland (1916), Germany (1917), France, Switzerland and the USA (1918). .

After the First World War, standardization was increasingly perceived as an objective economic necessity.

With development industrial production standardization began to develop also on an international scale. The constant expansion of international trade and the need for closer cooperation in the field of science and technology led to the founding International Association on standardization (ISA). In 1939, the work of ISA was interrupted by the Second World War.

Founded in London in 1946 International organization for Standardization (ISO), which included 33 countries. Currently, ISO is the largest international organization, uniting more than 100 countries.

§ 74. Voltage measurement. Extending the measurement limits of the voltmeter

Voltmeters, millivoltmeters and microvoltmeters are used to measure voltage. various systems. These devices are connected in parallel to the load, and therefore their resistance should be as high as possible. In this regard, the energy consumed by the device is reduced and the reliability of the measurement is increased.
To expand the measurement limits of the voltmeter, a multi-ohm resistance called additional resistance (r d). The connection diagram for a voltmeter with additional resistance is shown in Fig. 88.

With such a scheme from n parts of the voltage to be measured, only one part falls on the winding of the device, and the rest n- 1 part - for additional resistance. This happens because the resistance r d take more resistance of the voltmeter in n- 1 time, and with a series connection, the voltage is distributed proportionally to the resistance value.
Additional resistance

r d = r V ( n - 1) (99)

The total measured voltage is equal to the sum of the voltage drop across these resistances.
Number n shows how many times the measurement limit of the voltmeter is expanded.
Let the voltmeter we have allow us to measure voltage U in = 30 V, but you need to measure the voltage with this device U = 120 V. This means that we need to expand the limit of its measurement to

The additional resistance that must be connected in series to the voltmeter can be determined by the formula

r d = r V ( n - 1).

If the voltmeter resistance r in = 3000 ohm, then to expand the measuring limit of the device by 4 times it is necessary that the additional resistance

r d = r V ( n - 1) = 3000(4 - 1) = 9000 ohm.

After connecting an additional resistance to the voltmeter, each division of the instrument scale will correspond to a value in n times greater than indicated on it. For example, in our case, if the instrument needle points to 30, this will mean that the voltage

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