Datasets:
C 535 W53 917 Copy 1
EXPERIMENTAL ELECTRICAL TESTING
A COMPILATION, INCLUDING PRACTICAL ELECTRICAL MEASUREMENTS ACTUALLY PERFORMED BY STUDENTS
Weston electrical instrument company
MONOGRAPH B-4 AUGUST, 1917
SECOND EDITION
ISSUED FOR SCIENCE TEACHERS IN EDUCATIONAL INSTITUTIONS
"Everybody needs to know something about the working of electrical machinery, optical instruments, ships, automobiles, and saving devices, such as vacuum cleaners, fireless cookers, pressure cookers and electric irons, which are found in many American homes. We have, therefore, drawn up this book so that students may learn to think straight just as well by thinking about an electrical generator, as by thinking about a Gender tale."
From "Practical Physics." BLACK & DAVIS
WESTON ELECTRICAL INSTRUMENT CO. NEWARK, N. J.
Monograph COPYRIGHT, 1914. BY WESTON ELECTRICAL INSTRUMENT CO. QC535 WEB 1977 Copy1
CONTENTS
SUBJECTS
| Argument | PAGE |
|---|---|
| General Laboratory Work | 5 |
| Resistance Measurements | 7 |
| A Current Measuring Apparatus | 11 |
| Testing Fuses | 17 |
| Induction | 22 |
| The Photometer | 26 |
| Incandescent Lamp Testing | 32 |
| Electroplating | 34 |
| The Use of the Electric Motor in Efficiency Tests | 38 |
| The Electrolytic Cell | 40 |
| The Weston Direct-current Movable-Coil System | 65 |
| The Weston Alternating- and Direct-current "Movable-Iron" System | 68 |
| Co-operators | 70 |
| An Appeal | 78 |
EXPERIMENTS
- Resistance of a Conductor by the Substitution Method | 11 |
- Comparative Resistance of Various Conductors | 13 |
- Constructing and Testing a Lamp Bank Rheostat | 13 |
- Test of Fuses | 17 |
- The Fusing Capacity of an Electric Current | 21 |
- Current Induced by Magnetism | 26 |
- Currents Induced by Electromagnetism | 26 |
- An Exercise in Photometry | 28 |
- Practical Problems in Photography | 35 |
- Electroplating with Copper | 35 |
- The Electrochemical Equivalent of a Metal | 36 |
- The Electric Disk Stove or Hot Plate | 41 |
- Coolness of Objects by Means of an Electric Flattan | 47 |
- Boiling an Egg by Means of Electricity | 47 |
- The Immersion Heater | 48 |
- Making a Battery with the Use of Electricity | 48 |
- Testing a Nodon Valve with Dry Cells | 55 |
- Testing a Nodon Valve with a Direct-current Service Line | 56 |
- Testing a Nodon Valve with Alternating Current | 57 |
- Efficiency Test with Two Nodon Valves in Series | 59 |
- Efficiency Test with Two Nodon Valves in Series (Continued) | 59 |
- Puncturing the Insulating Wall of a Nodon Valve | 59 |
- Efficiency Test of a Commercial Electrolytic Rectifier | 62 |
A page from a scientific textbook on electrical experiments.
This is a scanned image of a blank page with a light brown background. The page appears to be from a book or document that has been scanned at a low resolution or has some form of damage or wear. There are no visible texts, images, or other markings on this particular page.
ARGUMENT
THE Weston Monographs were prepared with the definite object in view of attempting to co-operate with and assist science teachers in high schools and collegiate preparatory schools throughout this country.
Their context is exclusively on electrical subjects; and each deals with a particular theme.
For instance, B-1 dwells upon the manifest advantages of training students engaged in laboratory work by means of standard apparatus, and thus prepares them for the more advanced work after graduation. It also calls attention to the fact that it is inconsistent as well as unwise to attempt to perform modern progressive laboratory work by means of antiquated and obsolete apparatus. It shows what should be done.
B-2 contains a series of simple yet exceedingly instructive experiments, and presents suggestions that should be of great value in the preparation and simplification of an electrical course. It tells what could be done.
B-3 briefly describes several standard high grade and thoroughly reliable instruments, economical in price and particularly adaptable to high-school work.
In this Monograph B-4, we have compiled interesting and important data which will indicate some of the experiments which are actually being performed in progressive High Schools in these United States. We have accomplished this by reproducing the actual work of students, without their permission, together with sketches, data-sheets, reports and instructors' comments, as well as apparatus actually used.
We desire to explain as briefly as possible how B-4 has been produced.
Early in the Fall of 1913, we issued a letter to over 7000 science teachers on our list, in which we directed attention to the Monographs we had already issued, and requested suggest- 5 6 ARGUMENT
tions relating to experiments in electrical measurements which they would like to see embodied in future Monographs. We were immediately deluged with replies, and as soon as it was feasible we began preparing data relating to the experiments most in demand.
We then conceived the idea of asking science teachers to furnish us with these experiments, instead of preparing them ourselves; and wrote to a number of those who were fortunate enough to possess a modern equipment, inviting them to contribute some specified exercises.
In this way we hope to fulfill the requests of science teachers by publishing the work of other science teachers.
The experiments offered are reproduced verbatim; but we have in some instances either simplified or elaborated connection diagrams. Otherwise the authority for the execution of the work is vested in the contributor cited. Necessarily there was much repetition, and it obviously became practicable to print only such portions of the original as were necessary to gratify the request. It is therefore proper to gratefully acknowledge the assistance of those teachers whose work is not incorporated in this Monograph. Their tests were of great value to us and in many cases it was exceedingly difficult to make a choice.
Entirely aside from their intrinsic pedagogical value, the majority of these experiments have a significance which cannot fail to arrest the attention of the progressive instructor. They prove conclusively that the treatment given herein is toward the practical application of fundamental principles.
They indicate also that laboratory work requiring the use of instruments of precision may be successfully performed by young students of either sex.
In conclusion we desire to direct special attention to the Nodon Valve and Reutter experiments; because they are not only of great interest, but also because they possess utilitarian properties, in that they indicate how a teacher who has only alternating-current service available, may easily and cheaply transform to direct current; and thereby open up a greater realm of electrical experiments specially suited to the High School Laboratory.
WESTON ELECTRICAL INSTRUMENT COMPANY. GENERAL LABORATORY WORK
In preparing the minds of beginners in experimental electrical work, and in directing their attention to the ethical as well as the material considerations involved, it would be to their advantage to hear the following comments, which are adapted from an introduction to a loose leaf manual in Electrical Measurements. We are indebted to their author, Prof. James Theron Rood, Ph.D., of Lafayette College, for permission to use them.
I. PREPARATION FOR LABORATORY WORK
A well-trained experimenter, in any department of science, may at once be known by his ability to make clear, concise statements of the laws and phenomena of that department in which he is especially interested.
An electrical laboratory is a place designed to help men to acquire new characteristics; it is of value to no man only in proportion as he acquires his knowledge with the proper spirit, imbued with the desire to do and learn. The first requisite is to come to the laboratory knowing fully what you are to do, and how you are to do it. Read in advance the direction sheets for the given experiments, look up the references, be prepared to get the most out of your performance of the given experiment. If you do not come so prepared, you are almost sure to fail. In making observations, observe the order which must be followed. Required observations are likely to be omitted, time may be wasted on useless readings, interesting and valuable phenomena may escape your attention or be wrongly interpreted, and you may finish with a confused instead of a clear conception of the method and the value of the test. Make yourself master of the experiment, in the preparation for it, in the performance of it, and in the writing of the report
7 8 GENERAL LABORATORY WORK
about it. The students who must continually run to an instruc- tor for direction and advice can never rise very far.
II. PERFORMING THE EXPERIMENT
No general advice or directions can be given which will cover each and every experiment. Each test brings its own peculiarities, its own difficulties; but there are invariably certain things which mark the trained and careful experimenter. Some of these are given in what follows:
III. APPARATUS
All apparatus used in testing should be most carefully han- dled. What company would retain an employee who misused its instruments or machines?
Accidents may happen to even the most careful experimenters, but whenever they do occur, they should be reported of once. Please report injury to instrument back in its place without reporting its injury is the work of a sneak. Such action may result in the apparatus remaining unrepaired until a time when a co-worker, needing the apparatus for immediate use, discovers that it is injured and that it may have to be sent away for repairs. He is thus kept back in his work when, had the injury been known, suitable repairs might have been made before the apparatus was again needed.
IV. DIAGRAMS
Before beginning any experiment, make a clear diagram of the proper arrangement of all circuits to be used, with all connections, instruments, resistors, switches, cut-outs etc., shown clearly and accurately. Use heavy lines for indicating conductors carrying large currents, such as elec- tric power service wires, bus-bars, feeders for motors, etc., and light lines for potential circuits, such as leads to the e.m.f. terminals of wattmeters, voltmeters, etc. Submit this diagram to the instructor for his criticism and approval. Then connect up according to this diagram. Make no changes in it without the approval of the teacher. GENERAL LABORATORY WORK 9
V. INSTRUMENTS
Almost without exception all makes of ammeters have uninsulated metal binding-posts, while voltmeters have posts enclosed in insulation. The two kinds of meters can thus be at once told apart. Millivoltmeters are frequently used as ammeters by connecting shunts in the line, the potential drop across these shunts being proportional to the current; the readings of the meter when its leads are placed across the terminals of the shunt will be proportional to the current flowing, and may be read directly in amperes. When so used the values of the scale divisions of the meter will depend upon the particular shunt used, which will vary with each make. Every millivoltmeter must always be used both with its own shunt and its own leads. The shunt is always connected in the line and the millivoltmeter across the shunt. Remember, ammeters go in the line, voltmeters go across the line. Never lay instruments on the floor or on a chair. Always put them on a table and then pass the wires through holes in the edge of the table or else fasten them down with a clip or a rubber band. If any instrument is being pulled down onto the floor. If any instrument has a zero error reading, allow for it in your readings, or have it reset by means of its zero adjusting device. Never open or close a circuit at any ammeter binding post. Trace out the polarity of any D.C. circuit before connecting in an instrument. Be sure that the current flows through the instrument in the right direction. If it does not open the circuit before reversing any ammeter. Read all voltages at the CUT END, NOT AT THE METER. Read all meters to one-tenth of the smallest division. Look for any parallax when making a reading.
VI. ORDERLINESS
During the performance of all tests, see that all instruments, switches, lines, etc., are kept in an orderly condition and not allowed to become a confused mass. After finishing an experiment, see that all instruments, rheostats, lamps and other pieces of apparatus are replaced in their proper places in their cases. Coil up and put away all lengths of wire. Put everything 10
GENERAL LABORATORY WORK
back in its place and leave the apparatus as well as all the tables, etc., free from all wires and in perfect order ready for the next users. When finished replace covers on all motors or dynamos used. Next to success in the performance, orderliness in the handling of laboratory apparatus is the most important thing to be learned in a laboratory. Your care in this respect will be considered in determining your term grade.
VII. REPORTS
To be able to write a satisfactory report of an investigation is an art and accomplishment that should be the desire and pride of every engineer, in every walk of science. It is the keystone of all science. In its essence, an engineer's report is a why, a what, and a how of a thing done.
A good engineer must have knowledge, judgment and common sense. The laboratory, rightly used, is the best place for the development of such powers, and should be valued as such.
Let your laboratory motto be:
WORK—OBSERVE—THINK EXPERIMENTAL ELECTRICAL TESTING
EXPERIMENT NO. 1
RESISTANCE MEASUREMENTS
The following experiments were selected from a number kindly contributed by Mr. William F. Evans, Instructor in Physics, Girls' High School, Brooklyn, N. Y.
They are copied from the laboratory note-book of the girl who did the work.
A modification of these methods is used in shop practice for a quick and accurate measurement of resistance wires in course of manufacture. To eliminate errors due to a variation in current, the wire and the rheostat are both connected with one pole of the cell, and a double-throw switch is used, so that the rheostat may be adjusted until the same deflection is obtained when current is passed through either circuit in rapid succession. Reference, "Laboratory Exercises," Fuller and Brownlee, page 270.
Resistance of a Conductor by the Substitution Method
Apparatus. Weston ammeter; dry cell; rheostat; 50 cm., No. 30 German silver wire; and leads.
(1) Connect up the cell, the ammeter and the unknown resistance in series, being sure that all contacts are clean and all connections tight. See Fig. 1.
(2) Substitute the resistance box (with all plugs removed) for the unknown resistance and then decrease the resistance of the circuit until the current is the same as before. See Fig. 2.
(3) What then is the resistance of the 50 cm. No. 30 G. S. wire?
11 12 EXPERIMENTAL ELECTRICAL TESTING
STUDENT'S REPORT
(1) I connected up as in diagram the cell, the ammeter, and the unknown resistance (50 cm. No. 30 German silver wire),
D.C.AMMETER
Fig. 1.—Resistance Measurements. (Reproduced from Student's Sketch.) Evan' Method. Instrument Used is a Model 280, Weston Ammeter. Range 15 Ampere.
being sure that all contacts were clean and all connections tight. The indicated current was 6 amperes.
(2) I substituted the resistance box for the unknown resistance with all plugs out, and reduced the resistance of the circuit by putting in plugs until the reading of the ammeter was the same as before Resistance was 1.8 ohms.
D.C.AMMETER
Fig. 2.—Resistance Measurements. (Reproduced from Student's Sketch.) Evan' Method. Instrument Used is a Model 280, Weston Ammeter. Range 5 Ampere. COMPARATIVE RESISTANCES OF CONDUCTORS 13
(3) The resistance then of 50 cm. of No. 30 G. S. wire is 1.8 ohms, because the reading was the same when the resistance box was connected as when the German silver wire was connected.
EXPERIMENT NO. 2
COMPARATIVE RESISTANCES OF CONDUCTORS
Apparatus. In preceding experiment; together with other wires of various sizes.
OBSERVATIONS
| Length of Conductor | Area of Cross-section | Amp. | Ohms | ||
| (1) | 50 cm. G. S. wire | 05 sq.mm. | 60 | 1.8 | |
| Varying Lengths.... | 50 cm. G. S. wire | 10 sq.mm. | 1.4 | 5.4 | |
| Varying Lengths.... | 150 cm. G. S. wire | 05 sq.mm. | .20 | 5.6 | |
| (2) | 50 cm. G. S. wire | 05 sq.mm. | 60 | 1.8 | |
| Varying Lengths.... | 50 cm. G. S. wire | 10 sq.mm. | 1.04 | 8 | |
| Varying Lengths.... | 50 cm. G. S. wire | 15 sq.mm. | 1.34 | .5 | |
| (3) | 50 cm. G. S. wire | 05 sq.mm. | 65 | 1.9 | |
| Varying material.... | 50 cm. brass wire | 05 sq.mm. | 2.25 | .3 | |
| Varying material.... | 50 cm. copper wire | 05 sq.mm. | 370 | .4 |
Description. I connected up the German silver wire as in preceding experiment. Then I substituted the resistance box as in preceding experiment. First I used 50 cm., then 100, last 150 cm. of German silver wire. Next I used wire with 05 sq.mm cross section; then 10 sq.mm, finally, 15 sq.mm. After this I used 50 cm. of brass and 50 cm. of copper wire in place of the German silver wire.
March 21, 1883.
EXPERIMENT NO. 3
CONSTRUCTING AND TESTING A LAMP BANK RHEOSTAT
In commercial work, adjustable rheostats are extensively used; in fact, they are indispensable when current from service lines is employed for experimental purposes. 14 EXPERIMENTAL ELECTRICAL TESTING
For precision tests in laboratories, rheostat that are non-inductive and which have a negligible temperature coefficient are preferable and often necessary, but in general commercial testing adjustable lamp bank rheostats are most in demand for current regulation, or for building up a load.
The rheostat described in this experiment should appeal to the science teacher because it is simple in construction and yet permits a wide range of adjustment owing to the ingenuity of its design.
This rheostat was designed by Charles P. Rockwell, and constructed by him with the assistance of Gordon R. Mine, Barringer High School students, Newark, N. J. The tests made with it are their joint work.
A Complex Lamp Bank diagram.
Fig. 3—A Complex Lamp Bank.
Following is their own description:
This board was designed to allow any number of lamps, up to twelve, to be connected in multiple, series, or multiple series.
An oak board was obtained from the school shop. According to plan, Perkins 25 amp, double-pole single-throw switch and a fuse block were placed at the extreme right; four Perkins single throw, single-pole switches were placed next to these two for incoming and two for returning current. Two other Perkins switches placed next allowed current to cross over to different banks of lamps. Twelve sockets were screwed at equal distances from each other.
A complex lamp bank diagram.
Fig. 3—A Complex Lamp Bank.
TESTING A LAMP BANK RHEOSTAT 15
The small cut-out switches were made by bending copper stripes into jaws for receiving copper strips as blades. Holes were bored to receive jaws which were sealed in place with sealing wax.
Connections were made and lamps were screwed in as shown in Fig. 3.
APPARATUS AND MATERIALS REQUIRED
1 Weston voltmeter. 1 Weston ammeter. 1 portable testing set. 1 oak board 18 × 40 ins. 1 Perkins knife switch, 25 amp., double pole, single throw. 6 Perkins knife switches, 25 amp., single pole, single throw.
Sheet copper for making 27 switches (jaws and blades) which may be replaced with Trumbull single-pole, single-throw switches.
1 Edison double-plug cut-out. 12 Bryant porcelain receptacles, keyless.
IV, V, VI, VII, VIII. C, D, E, F, G, H, K, L, M, N, O, P, S, T, U, V, W, X.
Fig. 4.
A diagram showing a series of switches and fuses. The top row has three switches labeled "120 WATTS" and "750 WATTS". Below them are three fuses labeled "25 AMP." and "15 AMP.". The bottom row has two switches labeled "120 WATTS" and "750 WATTS".
C.P. lamps.
2 fuses, mica cap, 15 amp.
15 ft. No. 14 (B. & S. gauge) bare copper wire.
Directions for Operating Switches:
Note: All switches not specified closed must be open. For all lamps in multiple: Close III,
Fig. 5.
A diagram showing a series of switches and fuses. The top row has three switches labeled "120 WATTS" and "750 WATTS". Below them are three fuses labeled "25 AMP." and "15 AMP.". The bottom row has two switches labeled "120 WATTS" and "750 WATTS".
12 carbon filament 32
16 EXPERIMENTAL ELECTRICAL TESTING
For all lamps in series. Close III, VI, IX. A, F, I, K, Q, V, Y, W, P, G.
FOR MULTIPLE SERIES GROUPING
Three groups in series, each group containing four lamps in multiple. Close all except IV, V, VII, VIII, IX.
Two groups in series, each group containing four lamps in multiple. Close all except III, V, VII, VIII, IX.
A diagram showing three groups of lamps in series with multiple lamps.
Fig. 6. ARRANGEMENT
| Multiple Watts | No. of Lamps | Series Watts | MULTIPLE SERIES. See Fig. 4 | ||
| Groups of No. in Multi. | Watts | ||||
| 124 | 1 | 125 | 2 in series | 2 in multi. | 128 |
| 248 | 2 | 60 | 2 in series | 3 in multi. | 185 |
| 368 | 3 | 35 | 2 in series | 4 in multi. | 296 |
| 485 | 4 | 27 | |||
| 585 | 5 | 20 | |||
| 665 | 6 | 15 | |||
| 845 | 7 | 125 | 3 in series | 2 in multi. | 80 |
| 935 | 8 | 9 | 3 in series | ||
| MULTIPLE SERIES. See Fig. 5 | |||||||
|---|---|---|---|---|---|---|---|
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RESISTANCE PER LAMP
| Lamp No. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Res. Hot | 112 | 112 | 116 | 116 | 139 | 139 | 236 | 236 | 236 | 118.5 | 118.5 | 123.5 |
| Res. Cold | 235 | 230 | 240 | 230 | 235 | 235 | 245 | 245 | 245 | 235 | 235 | 240 |
R (hot) was when filaments were incandescent. Formula used $R = \frac{V^2}{W}$ or $R = \frac{118^2}{W}$.
R (cold) was when lamps were at room temperature ($22^\circ$ C.). Results were obtained by measurement with a portable testing set.
EXPERIMENT NO. 4 TEST OF FUSES
From Lafayette College, Department of Electrical Engineering, Laboratory Direction Sheets. Available through the courtesy of the author, Professor Foster H. Foster.
References: Bar, Direct Cur. Elec. Eng., p. 479; Swenson and Frankenfield, Vol. I, p. 342; Standard Handbook for Elec. Enga., p. 585; Foster's Handbook, pp. 4-5.
Purpose. Every electric circuit should be provided with some form of apparatus designed to prevent the flow of any excessive current which might start a fire or burn out any apparatus. The insurance companies require that all lighting and motor circuits shall be so fused or protected that the current-carrying wire shall never be overheated. Such protective devices are called cut-outs. They may be put into two classes, fuses and circuit-breakers. Fuses, according to their arrangement, may be divided into three classes, open, expulsion and enclosed. Circuits carrying large currents are more expensive than those carrying less current and occupy more space. They are better for circuits carrying large current, or where the circuit is liable to be opened or overloaded frequently, since they are more sure of opening the circuit.
Construction. Fuses are merely strips of metal of such shape and material as will fuse or "blow" before any excess current can flow for any length of time. The I. R. losses in the metal due to the current passing causes the strip to become 18 EXPERIMENTAL TESTING
heated. If the heat is generated faster than it can be radiated, the fuse material melts and the circuit is thus opened, provided the arc does not hold between the terminals of the fuse block on account of the melting vapor which may be left in the space between them.
This limit is the amount of current which a given fuse can safely break, unless there is provided some means of expelling the hot vapor (expulsion fuses), or of condensing it (enclosed fuses). In this last the vapor is supposed to be immediately condensed in the spaces between the granules of the non-inflammable, non-conducting material which fill the tubes. On account of the variations in the alloy of the different parts of the fuse wire, and on account of the direction of air currents, open fuses cannot be depended upon to always blow at the same current with the same length and diameter of fuse wire. For open fuses alloys of lead, antimony and bismuth are mostly used. Enclosed fuses are mostly of zinc. For large fuses copper is sometimes used, but it is liable to hold the arc through its vapor.
Object. The object of this experiment is to test some commercial fuse wire and to determine the relation (a) between length and the fusing current, (b) between diameters for this last, (all diameters of wires tested should be of the same make), (c) to investigate the construction and action of some types of enclosed fuses.
Apparatus. Various diameters of fuse wires, fuse block with adjustable terminals, adjustable resistor, Weston ammeter and inch scale, also line switch.
Part I. Set the terminals of the fuse block 1/4 inches apart in the clamp and insert a length of fuse wire. Connect the fuse block in series with an ammeter, adjustable resistor and switch; and connect the whole across the D.C. supply circuit. See that the resistance is set to allow only a small current to flow, close the switch and slowly increase the current until the fuse blows. Repeat with the same size of wire for fuse lengths of 2, 2½, 3, and 3½ inches. Repeat this series for all the different diameters of wire given you. Record make off wire, rated capacity, and blowing current. Calculate and record the percentage ratio between the rated capacity and the blowing current. Note carefully the construction of each fuse.
A diagram showing a fuse block with adjustable terminals, an ammeter, an adjustable resistor, and a switch connected across a D.C. supply circuit.
THE FUSING EFFECT OF AN ELECTRIC CURRENT 19
Report. Describe what you did. Plot curves showing (a) relation between length and fusing current for wires tested, (b) relation between diameter and fusing current for a given length of fuse. The form of curve for this last is usually:
where $d$=diameter of wire;
$I$=fusing current, and
$a$=constant depending on the composition of the wire.
Give good sketches of the construction of the enclosed fuses tested and give description of the details of each.
Questions: (a) Does the size or mass of the terminals of the fuse block affect the value of the fusing current?
(b) If so, how?
(c) Would this effect be proportional for all lengths of the fuse wire? Why?
(d) Why should the current in every case be increased slowly?
(e) Why should the enclosed fuses be given a preliminary heating before being blown?
EXPERIMENT NO. 5
THE FUSING EFFECT OF AN ELECTRIC CURRENT
The following experiment on fuses was supplied by Mr. Milton M. Flanders of the Bliss Electrical School, Takoma Park, Washington D. C. It is so clean-cut and practical that comments are superfluous. Sketch is a reproduction of the one sent in by the students performing the test.
TEST NO. A-400
Heat
A study of the fusing effect of an electrical current.
Object of Test
To determine the current and time required to melt fuses under various conditions. 20 EXPERIMENTAL ELECTRICAL TESTING
APPARATUS REQUIRED
| 1 ammeter (0-100) | Various fuses |
| 1 rheostat | 1 circuit breaker |
| 1 stop watch | 1 switch |
| 1 thermometer | Connecting wires |
CONDUCT OF TEST
I. Preparation. Set up the apparatus as per diagram, connecting to a source of low potential and high current, as a stor-
A simple electrical circuit diagram with a rheostat, battery, ammeter, and stopwatch connected in series.
Fog. 7.--STUDY OF THE FUSING EFFECT OF AN ELECTRICAL CURRENT. (Reproduced from Student's Sketch.) Flanders' Method.
Instrument Used was a Model L, Weston Ammeter. Range 100 Amperes.
Note.--For all ordinary laboratory work, fuses that will "blow" at 1 to 20 amperes will suffice, and an ammeter of lower range than the above will be preferable.
age battery. Close switch $S$ and after inspection by instructor, admit current and correct polarity of ammeter if necessary. See Fig. 7.
II. Operation. (a) Admit current to 200 per cent rating of fuse under test, holding this constant by means of the rheo- stat $R$. Open switch $S$ and simultaneously start stop-watch. Note the exact time required for the fuse to open the circuit. Repeat at least three times.
(b) Repeat above on different fuses, as directed.
(c) Repeat above on increasing current, the rate of increase being 1 ampere per minute, and tabulate results. THE FUSING EFFECT OF AN AMMETER CURRENT 21
(d) Repeat operation (a) with the fuse wire in contact with some foreign insulating substance. (e) Repeat operation (a), first raising temperature of fuse 50° C., by means of a heating chamber.
TEST CHARTERIZATION. Results all results indicated below:
| Fuse. | Wire. | Length | Deg. C. | Rating Amps. | Time. | Note. |
| Link | Shawmut | 1.625 | 17.8 | 6 | 12 | 10 11 11 Avg.10.66+ |
REPORT ON TEST No. A-400 Instrument used: Weston Model 1, Ammeter No. 5378. Centigrade Thermometer No. 4.
DATA OPERATION (a)
| Type. | Wire. | Length In. | Temp. Deg. C. | Rating Amps. | Amps | Time, Sec. | Remarks |
| Daum | Shawmut | 1.625 | 22 | 6 | 12 | 8.6 | Average Time |
| Daum | Shawmut | 1.625 | 22 | 6 | 12 | 7.2 | |
| Daum | Shawmut | 1.625 | 22 | 6 | 12 | 10.0 | 8.03+ sec. |
OPERATION (b)
| Type. | Wire. | Length In. | Temp. Deg. C. | Rating Amps. | Amps | Time, Sec. | Remarks |
|---|---|---|---|---|---|---|---|
| Link Link Link | |||||||
| Shawmut Shawmut Shawmut | |||||||
| 1.625 1.625 1.625 | |||||||
| 17.8 17.8 17.8 | |||||||
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