Motion picture electricity

Front matter

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G PICTURE WOKLD

: , :: 17 Matliscn Avenue VtQKKGITY

Foreword

THE motion picture industry has within a very short time expanded to such tremendous proportions that the call for experienced managers and operators has been greater than the supply. Mechanics and electricians, in general, have qualified themselves as motion picture operators. There are, however, conditions to be met with in practice which require special knowledge in this particular line.

In order, in a measure, to assist the operator in securing education concerning the fundamental principles involved and the best methods of getting perfect results, the writer herewith presents a reproduction of his "Electrical Talks," which appeared in the Film Index some time ago. There is also included additional new matter and valuable data and tables which will be of interest to the proprietor, manager and operator of motion picture theaters.

The day has passed when "any old thing goes." The public insists upon perfect pictures and perfect projection, and it is incumbent upon each individual proprietor to meet this demand. The operator is the man behind the gun — he has to stand the brunt if the picture is not brilliant and if things don't go right generally, as far as the picture is concerned. He is the man whom I want to, and can assist, and a careful study of the following pages will make many operators better qualified to secure ideal results.

I do not contend that there are not other ways to accomplish results than those set forth within these pages, but I do claim that if these instructions are followed the best results will be obtained.

Mr. Manager: You are conducting one of the most beneficial and educational institutions of the country.

Every motion picture theater, properly conducted, is, as I might say, a recreation and resting place for the overworked brain and from an educational and amusement point of view it has no parallel because you teach without language through the eye to the brain by means of motion and acting, making everybody, foreigner or native, understand alike. Therefore, you must do your part to make this transmission of intelligence without words as clear, easy and restful as possible by making your picture stand out bold, steady and clear on your screen.

Publishers' Note

Following a plan outlined a few years since, the publishers of The Moving Picture World take pleasure in adding this volume to their standard publications for the moving picture industry.

This book covers the very important end of the picture theater electrical equipment. Its author is well known throughout the trade, and through his extensive experience is particularly well equipped for the preparation of this volume.

The publishers trust and believe the book will prove a valuable help. It contains complete, practical and technical information which should answer the requirements of every reader, as well as standard tables of electrical and kindred subjects that are in constant use in the trade. We consider each department in this publication to be of the highest possible worth to those interested in motion picture exhibiting. Therefore, we highly recommend it as a technical authority.

Chalmers Publishing Company July, -1914

Technical Section

CHAPTER I Electricity

THAT magnificent and most wonderful force or power, which almost runs the world, has in no little measure contributed to the phenomenal success of the motion picture industry. In justice to yourself, to your business and to your patrons, you must become more familiar with the functions and the general application of electricity in your theater so that you may economize and improve the results to the greatest possible extent.

There is no substitute, at the present moment at least, for the electric current as a means for advertising your place of business ; illuminating your theater and for projecting brilliant pictures.

The economical application and most practical selection of the many different kinds of current and appliances for motion picture theaters is not so thoroughly and generally understood by the average electrician as one would believe. Experience in all branches of the electrical business, including designing and manufacturing electrical apparatus, electric wiring, installation of electrical machines, ventilating systems and fittings of all kinds, generating and distributing electric current, and last but not least, thorough knowledge of the requirements of motion picture theaters in particular, must be the accomplishments of your electrical advisor.

The most difficult part of my problem will be to make everything clear and plain to you, but I am sure that if you will carefully read each line you will understand ; read it again and again so that you will remember it.

Before discussing electrical equipment in detail, we will first become familiar with the meaning of electrical terms and names.

VOLTAGE

Voltage is the word which signifies the pressure of the electric current on or in an electric circuit.

Voltage is also represented by any of the following words which practically mean the same thing : Potential, Electro-Motive-Force, Electric Pressure. These are the most common.

Voltage represents the pressure of an electric system or service just the same as pounds per square inch represents the pressure in a water, steam or compressed air pipe.

To give you a practical illustration by which you can judge voltage, I may say that an ordinary electric battery such as used for telegraph and fire alarm systems gives a pressure of just about one volt. Now if we take no such batteries and connect them in series one after the other, we will have between the first and the last wire a potential or voltage of no volts.

Electric batteries which produce electric current by means of chemical action are not practical for heavy or continuous work, therefore, electric dynamos or generators, which produce almost any desired voltage and current by the use of mechanical power to drive such generators are necessary and are universally used for the supply of current on a large scale.

TESTING VOLTAGE

Voltage is measured by a volt meter, which may be attached to the two wires to be tested. Another method of testing voltage roughly is to connect two incandescent lamps of the same candle power, each one of no volts, in series. If both lamps burn bright, that is, giving the normal candle power, you know that the circuit delivers about 220 volts. If the lamps burn very dim, giving only one-quarter of the normal candle power, the circuit delivers about no volts. This method of testing with lamps is not recommended as being accurate or final, but may be used by the traveling exhibitor in determining for himself before he connects his machine circuit, whether the no or 220 volt rheostat should be used.

Suppose you have a water pipe one mile long and at the end of it there is a faucet and just ahead of the faucet a water pressure gauge is connected to the pipe, and the gauge indicates no pounds. Now open the faucet and you will see that the pressure gauge needle will fall back, depending upon the size of the pipe and bow wide you open the faucet. If the pipe is very small, the friction which the water creates in flowing against the wall of the pipe will cause the pressure at the end to drop very low.

Just so is the voltage of a circuit affected. If you have two small wires running a distance of a mile and at the end of the wires we connect an arc lamp, a quantity of incandescent lamps, or a motor, the voltage, when the arc lamp is not burning, is no. When the load is switched on, the voltage may drop very low if the wires are not large enough, due to the friction or resistance offered by the wire to the flow of current; and it is evident that the arc lamp, the incandescent lamps, or the motor at the end o>f your wires will not operate properly. I believe that the foregoing explanation will give you a good idea of the word or term voltage.

AMPERE

Ampere is the word which signifies the quantity or volume of electricity flowing through an electric circuit, arc lamp, incandescent lamp, motor or other machine, connected to the circuit.

The measurement called "gallon" in the water system, or cubic foot for gas, designates quantity or volume. So does the ampere in the electric system.

Remember, at the end of the water pipe referred to under the heading "Voltage," page 10, we had a pressure of no pounds on the gauge when no water was flowing and also at the end of the electric circuit we had no volts when the wires were not connected to the arc lamp, or other load. The reason why the water gauge showed full no pounds or the volt meter no volts, at the end of the pipe line or the electric circuit, was that the faucet was closed or the electric wires were not connected to a load. There were no gallons of water flowing through the pipe and there were no amperes flowing through the electric wires, consequently no work was done and there simply remained the pressure at the end of the pipe or at the end of the wires ready to do work.

As the diameter of the pipe has to be larger in order to carry more gallons of water, so does the electric wire have to be larger in order to carry more amperes. Otherwise the friction in the pipe or the resistance in the wire will use up the pressure or voltage before we get to the faucet or to the arc lamp, making the flow of gallons very low or the flow of amperes much less than it ought to be. From the above, you can make up your mind that :

The size of the wire required for an electric circuit depends entirely upon the number of amperes required for the electric installation.

To give you an idea of the general amount or volume of an ampere I might tell you that one 16 c.p. carbon filament lamp on no volts requires about one-half ampere; one regular enclosed arc lamp, such as are usually furnished by the electric lighting companies, requires about 5 amperes on no volts; one d. c. arc lamp for motion picture machine requires about 30 amperes.

OHM

Ohm is the word or electrical term which signifies the unit of resistance offered to the passage or transmission of an electric current on or through an electric wire or conductor.

The legal ohm is the resistance of a mercury column one square millimeter in cross sectional area and 106 centimeters in length.

The ohm represents, in other words, "resistance" of electric conductors and machines and stands for the same thing as the friction in a pipe carrying water, gas or air, In everyday discussion of electrical matters by the user of electrical machines, the word ohm is not employed, but the word resistance being more common and easily understood is generally used.

Under the heading "Voltage," page 10, we discovered that the voltage at the end of an electric circuit may be considerably lower than the voltage at the point where the current is generated and that the voltage drop was due to the flow of ampere through the circuit, in other words to the friction or resistance offered by the wire to the flow of current. The voltage was used up in pushing the current through the wire just the same as water pressure is used up in pushing water through a pipe. When anything is moved from one point to another there is a loss depending upon the resistance offered. For instance, if you wish to move a ioo-pound weight from one point to another it induces a loss of power or energy depending upon the friction or resistance which, however, can be modified by using different means for reducing or increasing the friction. If the ioo-pound weight is set on a rough board it is difficult to move it because the rubbing of the weight against the board causes friction and the rougher the board the greater the friction and consequent power required to move the weight. This power is lost in the shape of heat, generated on the two rubbing of the weight against the board causes friction smooth less power would be required in moving the weight because the friction and consequently the heat loss is less. If we mount the weight on wheels or ball-bearings then much less power would be required in effecting the movement because the friction is then reduced to a minimum.

This example serves us very well in getting a clear understanding of resistance due to friction in moving anything from one point to another. Just so is the resistance or friction with consequent loss generating heat in electric wires and machines due to the resistance offered by the wire to the passage of the current, depending upon;

(i) The size or diameter of the wire.

(2) The material from which the wire is made.

(3) The amount of current in amperes to be forced through the wire.

We now understand that whenever resistance is introduced heat is generated and power is lost; therefore, we should reduce the resistance in all electric circuits and machines to the lowest possible amount in order to save electric. energy which costs money to produce.

Copper is the material which for practical purposes offers the least resistance to the passage of electrical currents ; therefore copper is used for conducting wires and for all kinds of electrical machine windings.

If we want to generate heat by means of electricity, then we introduce a wire made of some other material than copper, which offers greater resistance to the passage of electric current as is the case in electric heaters which are made of porcelain, with a wire made of nickel and copper, or nickel and steel, wound upon the porcelain through which the current passes, thus heating the wire.

If we wish to produce light with electricity, then for the incandescent or glow lamp there must be used a wire or conductor of very high resistance which glows yellow or white, depending upon the style of the lamp.

If still more brilliant light is required it may be produced by the electric arc between two metal or carbon points. In this case, the resistance is the air space between the two points, which is so great that the current ordinarily used for electric lighting cannot jump across even the smallest air gap. In this case, the carbons must be put in actual contact before the "arc" can be started, and then the heat vaporizes the points which forms a gas, to take the place of the air, and this gas maintains the "arc" and permits the separation of the points forming what is ordinarly called an "arc light."

In order to give you an idea of the comparative resistance of different kinds of materials, I will mention them in the following order from the lowest to the highest : Silver, copper, brass, zinc, iron, nickel, carbon, plumbago, moist earth and water.

You may be surprised to learn that if I take a copper rod one-half inch in diameter, 10 feet long and take a glass pipe one-half inch inside diameter, 10 feet long, filled with water, the resistance of the water in that pipe is to electricity 6,754 million times greater than the resistance of the copper rod.

This may surprise some motion picture operators who have been using water for resistance in place of a rheostat, but it is nevertheless a fact that water cannot be used for a rheostat, unless something else, like salt, for instance, is put into the water in order to lower its resistance, as otherwise you could not force any current through the water rheostat.

Operators who have used the earth as a resistance by driving pipes into the ground, or by putting metal plates on the bottom of a pond or lake, get a current through the moist earth and not through the water, unless the water is salt or is in some other way made a conductor.

There are two kinds of resistance; one is due to the friction offered by the conductor, or wire, to the flow of the current which is usually called "Ohmic Resistance."

The other kind of resistance is due to the magnetic kick, or reaction, in an electric circuit or machine and is usually called "Inductive Resistance."

While it is present with direct current systems it is not noticeable unless in special cases, but it is always a big factor when alternating current is used, and it is taken advantage of in several ways in order to do away with the rheostat for the control of arc lamps, as will be referred to later on.

WATT

Watt is the word which expresses the unit of electric power. One thousand watts are called one kilowatt and when one kilowatt is used for one hour a certain quantity of power has been produced and used, which is called one "kilowatt hour."

In order to abbreviate these terms kilowatt is writtenand spoken of as k.w. and the kilowatt hour k.w.h.

The kilowatt hour is the unit or measure by which electric power is made and sold, and this term is used all over the world.

The watt .is the product or effect of voltage multiplied by amperes. For instance, if we have a circuit on which there is a voltage of ioo, and we operate a moving picture arc lamp on direct current, taking 30 amperes, we multiply 100 by 30, which gives us 3,000 watts, which equals 3 kilowatts, or in abbreviated form 3 k.w. If we burn this arc lamp for one hour there will be consumed 3 kilowatt hours, therefore if the rate is 10 cents per k.w.h. it would cost just 30 cents for one hour.

If we burn this same arc lamp only one-half hour it is evident that the watt consumption will be just one-half or 1,500, which equals iy 2 k.w.h. and the bill for electric current will therefore also be one-half, or 15 cents.

Electricity is different from all other powers or forces because it cannot be measured by volume, but only by its effect.

When you buy water from the water company you get pressure as well as a certain number of gallons of water. The pressure may be used for driving a water motor or lifting a piston elevator and besides you have the original number of gallons of water left after the zvork has been done.

When you buy electricity from the electric lighting company, you secure and pay for a certain effect which may be represented by power, heat or light, but after you have secured this effect you have nothing left. In other words there is no evidence of you having received anything but the work done on the instant.

In order to give you a practical understanding of what you get when you purchase 1 k.w.h., I may say that 1 h.p. as usually applied to a steam engine equals exactly 746 watts, or three-quarters of a k.w. If you operate a 1 h.p.

steam engine for one hour you have used I h.p. hour, and for an ordinary engine this would require about 10 pounds of coal.

Now, if you substitute a I h.p. electric motor for the i h.p. steam engine the motor will require about 746 watts, or three-quarter k.w.h. to do the same work, and the expense at the 10 cent rate would be just 7^2 cents for one hour's operation.

I am giving you these examples in order that you may have it impressed upon your mind that electric power is in many respects similar to steam or water power and also to get you familiar with the comparative values of electricity.

The ohm is the unit for measuring resistance in electric circuits and machines.

Resistance is that property in a wire or other material which opposes a movement of any kind and is generally applied to represent the friction in an electric wire. The resistance should be kept as low as possible in order to reduce the heat loss and consequent expense for electric power uselessly wasted.

The kilowatt hour is the unit of measurement for electric power, and is the product of the voltage multiplied by the amperes for all direct current systems.

KILOWATT HOUR

Before going into details as to how to figure kilowatt hours from voltage and amperes, I will give you further explanation.

Suppose you hire a man capable of pumping sufficient water to fill a tank on your roof, and that it takes this man working with normal power and exertion ten hours to do the work, and you pay the man $1.50 or 15 cents per hour. At that rate you are paying 15 cents for each man hour. If you wanted to do this same work in one hour's time, you would have to put in ten pumps, employ ten men and at the rate of 15 cents per hour, the total expense would be just $1.50, but you would have the work done in just one-tenth of the time and the only extra expense to you would be the investment for the nine extra pumps, providing you could get the ten men just when you want them.

It is generally agreed that one man power equals about one-eighth to one-fourth horse-power, depending upon the length of time the man is compelled to work. In other words, a man can produce about one-eighth horsepower continuously for ten hours. It is, of course, understood that he may have to rest for a while, but no man can produce one-fourth horse-power continuously, only for a period of one-half hour, unless in exceptional cases.

We have learned that one horse-power equals about three-fourths k.w., but allowing for all losses in the motor and the belt it takes about one k.w.h. to produce one horse-power. Therefore, one-eighth of a horse-power would require just one-eighth of a k.w., or 125 watts per hour.

If we put an electric motor on the above mentioned pump, it would consume about 125 watts per hour, which for ten hours would be 1,250 watts or 1% k.w., which at the 10 cent rate would represent an expense for current of 123^ cents. This one-eighth horse-power motor would have to run steady for ten hours to do the work, and you understand, of course, that the electric light company would have to< furnish boiler, engine, dynamo, feed wires, transformer and meter large enough to drive this one-eighth horse-power motor and that the electric company would furnish you this quantity of power in ten hours' time, giving them a good, steady load at the expense to you of 12^ cents.

Now, if you want to do this work in one hour, you would have to put in about i 1 /^ horse-power motor and you can readily understand that the electric light company would have to put in much larger electric generating equipment in order to supply you at the same 10 cent rate for current, the income to the electric company would be just about 123/2 cents, but the expense would be much greater because the company has to invest more money and run a bigger plant if you want your work done in one hour.

That is the reason for the electric company in many places charging according to the number of hours you use your installation; therefore, when you put in your equipment you must do it in such a way that you have the smallest possible amount of installation or, as I might call it, "demand" on the electric company's service, in order to secure the lowest rate. The current saver for the motion picture machine lamp cuts your demand in half, not only cutting your old bill 50 per cent., but in some instances also reducing the rate, if the electric company has a rate on the sliding scale, as many of them have.

We all know that it costs more to put up a building in two months than to put it up in six months, because rush work means more expense in every way, and I want to impress this on your mind, because in laying out the electric equipment for theaters, considerable reduction can be made in the current consumption as well as in the rate, especially if the company has a sliding scale of rates. I have deemed it advisable to give you the foregoing example, because you must realize and understand these fundamental principles, and any time you spend at familiarizing yourself with the illustrations given will save you a great deal of misunderstanding and expense and it will also give you a clear idea of why the electric light company charges different rates for different classes of service.

As a comparison and standard of values, I will say that:

One 16 c.p. carbon filament lamp takes about 50 watts per hour.

One regular enclosed arc lamp takes about 500 watts per hour.

One 4,000 c.p. flaming arc lamp takes about 50G watts per hour.

One 12-inch fan motor takes about 50 watts per hour.

One 16-inch fan motor takes about ioo watts per hour. One ceiling fan takes about 125 watts. One 18-inch exhaust fan takes about 250 watts per hour.

One 24-inch exhaust fan takes about 400 watts per hour.

One 36-inch exhaust fan takes about 1,000 watts per hour, or 1 k.w.

One ordinary moving picture lamp on direct current with rheostat on no volts takes about 3,300 watts per hour, or 3 3-10 k.w. This same moving picture lamp on 220 volts takes 6,600 watts or 6 6-10 k.w. per hour.

One moving picture lamp with rheostat on alternating current no volt circuit takes 4,500 watts or 4 5-10 k.w. per hour. This same lamp on 220 volts takes 9,000 watts, or 9 k.w. per hour.

Keeping this data in mind, you can easily figure for yourself how many watts or k.w. your installation requires.

FORMULAS

For the electrician and operator as well as the manager or proprietor who may be interested, the following data and formulas are of great value in figuring voltage, amperes, resistance and watts.

Formula No. 1

E

C =

R

Formula No. 1 is the electrical designation for figuring the number of amperes which will pass through a rheostat when you know the voltage and the number of ohms of your rheostat. For instance, if you have a line voltage of 100 and your rheostat has a resistance of 5 ohms and you want to find out how many amperes will pass through the rheostat, the formula extended in simplified form will read :

Amperes equals , or, written out: ioo

5 ohms volts divided by 5 ohms equals 20 amperes, and this is the amount of current you would get through your rheostat, which would, in that case, be nothing more than an electric heater taking 20 amperes from the 100 volt line.

Formula No. 2

E

R =

C Formula No. 2 is the electrical designation for figuring the number of ohms for resistance required in your rheostat when you know the line voltage and the number of amperes required for your work. For instance, if you have 100 volts and you require 20 amperes for your work, the formula in simplified form reads as follows :

Resistance in ohms of rheostat equals ,

20 amperes or written out: 100 volts divided by 20 amperes equals 5 ohms, which is the resistance required in your rheostat.

Formula No. 3

E = CxR

Formula No. 3 is the electrical designation for figuring the number of volts required to force a certain number 'of amperes through a rheostat of given resistance. For instance, if you have a flow of 20 amperes through a rheostat offering a resistance of 5 ohms, the formula in simplified form reads as follows :

Voltage equals 20 amperes x 5 ohms, or written out : 20 amperes times 5 ohms equals 100 volts. In other words, it would take just 100 volts to force 20 amperes through a rheostat having a resistance of 5 ohms.

Formula No. 4

W=CxE Formula No. 4 is the electrical designation for figuring the number of watts which will be delivered by a given voltage and flow of amperes on a D. C. and for A. C. where the load is made up of only "ohmic" resistance. It cannot be used correctly for A. C. where motors, arc lamps and current savers are used, as such a load has in addition to "ohmic" resistance what is called "inductive" resistance. For instance, if you have on D. C. system a flow of 20 amperes and the voltage is 100, the formula in simplified form reads as follows:

100 volts x 20 amperes equals 2,000 watts. In view of the last formula, you can easily remember that

For all D. C. systems it is only necessary to multiply the line voltage by the amperes flowing through the circuit in order to find the number of watts required.

In explanation of these formulas remember the following:

C stands for current in amperes.

E stands for the line voltage or the voltage at the point where test is made.

R stands for resistance, of the rheostat or machine, in ohms.

W stands for watts.

The amperes flowing through a circuit or machine are equal to the voltage, divided by the resistance in ohms.

The resistance in ohms of a circuit or machine is equal to the voltage divided by the amperes flowing.

The voltage at the terminals of a circuit or machine is equal to current in amperes flowing multiplied by the resistance in ohms.