The current may be read by an ammeter, and the potential difference by a low-reading voltmeter (see Electrical Measuring Instruments).
The voltmeter enables the voltage of the charging generator to be kept above that of the battery, as the latter rises during charge.
A convenient way is to connect the terminals of the several cells to jacks on the power board and to terminate the voltmeter in a plug.
The volt side of the dial may be calibrated in the same manner, using a voltmeter instead of the ammeter.
Home-Made Battery Voltmeter [153] Secure a piece of brass tube 3 in.
To make a voltmeter out of this instrument, wind with plenty of No.
Illustration: Battery Voltmeter Construction] tube and solder a piece of copper wire to it; the other end of the copper wire being hooked to the spring, C.
If this does not cause the voltmeter pointer to return to the "0" line, replace the wire and see paragraph (d).
If this causes the voltmeter pointer to return to the "0" line, the switches are defective.
If they are, separate them and see if the voltmeter pointer returns to the "0" line.
If the voltmeter pointer does not move from the "0" line on the scale, complete the battery connections by fastening the positive battery cable to the positive battery terminal, and make the test described in Section 2.
If this causes the voltmeter pointer to return to the "0" line, the cutout is defective and a new one should be installed, unless the trouble can be found by inspection and repaired.
Testing jar for leaks, using a voltmeter in series with test circuit] This test may be made by using a voltmeter instead of lamps, as shown in Fig.
If this causes the voltmeter pointer to return to the "0" line, the starting switch is defective.
To detect such trouble, connect a voltmeter (which has sufficient range to indicate the battery voltage) between the positive battery cable and the positive battery terminal.
If they are not, open them and see if the voltmeter pointer returns to the "0" line.
Remove the voltmeter and complete the battery connection.
If this causes the voltmeter pointer to return to the "0" line, the cutout points are stuck together or the cutout is defective, and the generator should be taken apart for inspection.
If the voltmeter pointer does not return to the "0" line when the battery or ammeter wire is disconnected from the cutout, see paragraph (d).
If the voltmeter pointer does not return to the "0" line, replace the wire and consult paragraph (d).
A small transformer without an iron core, of course, was used to bring the reading within range of a Cardew voltmeter by connecting the voltmeter to the secondary.
The nodes may also be investigated by means of an ordinary Cardew voltmeter which should be well insulated.
Between grid and filament there is placed a voltmeter which will tell how much e.
We must be careful that the voltmeter is so made that it won't offer too easy a path for electrons to follow.
Of course, we must let a small stream of electrons flow through the voltmeter so as to make the pointer move.
Then the Highway Commissioner who had just been taking a set of voltmeter and ammeter readings on an audion moved that there should be a new road known as "Audion Characteristic.
Illustration: Fig 17] Suppose the ammeter shows a current of one ampere and the voltmeter an e.
Voltmeter and Ammeter of the Weston Instrument Company.
We read the voltmeter in the plate circuit and the ammeter in that circuit.
This circuit is the same as we used to find the audion characteristic except that there is a clip for varying the number of batteries in the plate circuit and a voltmeter for measuring their e.
X, for the pointer will take the same position as it did when the voltmeter was connected between n and d.
Next we read the voltage impressed on the grid by reading the voltmeter in the grid circuit.
Now connect a voltmeter to the two ends of the coil as shown in the figure.
If we connect a voltmeterto the battery X as in Fig.
These are so connected that the drop in pressure across them will be combined with that of the pressure transformer, so that the voltmeter reading indicates the pressure at the center of distribution or end of the line.
Synchronism is shown by the lamp remaining out, or the voltmeter at zero.
If the machines be out of step, the lamps will fluctuate in brightness, or the voltmeter pointer will oscillate, the pulsation becoming less and less as the incoming machine approaches synchronous speed.
How can thevoltmeter indicate the pressure at the center of distribution?
The simplest arrangement consists of a lamp or preferably a voltmeter connected across one pole of a two pole switch connecting the incoming machine to the busbars, the other pole of the switch being already closed.
In order to do this a device which is known as a "line drop compensator" is placed in the voltmeter circuit as shown in the diagram, fig.
The same voltage transformer serves for both voltmeter and compensator.
A graphic demonstration of the improvement in voltage regulation, which has been secured in this case, is given by the curve drawing voltmeter records reproduced in fig.
This relay is practically a voltmeter arranged for making and breaking contacts with fluctuations of voltage.
It consists of two voltmeter electromagnets acting in opposition on a disc attached to the pointer shaft.
The reactance and resistance are both so wound that any proportion of the winding can be cut in or out of the voltmeter circuit.
By means of a double pole double throw switch, the voltmeter can be made to read the pressure on the secondary of either transformer.
Supposing the same change ratio it is evident that if both remain unloaded the voltmeter will indicate the same pressure.
Connect voltmeter and wattmeter as shown in the illustration to the low tension side of the transformer.
This drop can be read as the difference of the voltmeter indications, and when expressed in per cent.
If one of the transformers be reversed the voltage will be almost doubled; in fact, it is a good plan to check up all the transformer connections with the voltmeter or lamps which will often save a burn out.
An ammeter, voltmeter and wattmeter are required to make the tests.
At such a rate, unless the constant voltage method be employed, the cell may be considered full when the voltmeter reads 2.
Each cell should be tested with a low reading voltmeter and hydrometer about once a week.
From this point the charging should be prolonged until the pressure, as determined by a voltmeter or a cadmium tester, rises to about 2.
A voltmeter is required with a three-way switch to connect it to the dynamo, battery or lamps, and a circuit breaker must be inserted in the battery circuit in order that it may be opened when the current becomes excessive.
To do this, a low-reading voltmeter must be used with prods attached to the voltmeter leads that can be forced into the terminals so as to insure good contacts.
In the diagram the voltmeterandvoltmeter connections have been omitted.
To do this you need only to use a voltmeter across the filament terminals instead of an ammeter in series with it; then regulate the voltage of the filament with a rheostat.
Don't fail to use a voltmeter to find the proper temperature of the filament.
The filament voltmeter is connected across the filament secondary coil terminals, while the plate milli-ammeter is connected to the mid-taps of the plate secondary coil and the filament secondary coil.
Since this is to be a voltmeter and it is always desirable that a voltmeter take as small a current as possible, the winding must consist of a relatively large number of turns of small wire, each turn carrying a small current.
The instrument may be used as either a voltmeter or as an ammeter, and its operation will be identical in each case.
Illustration: A Wood Mandrel Used to Face the Ends and Turn Flanges on Tubing for Cylinders] A Pocket Direct-Current Voltmeter The assembled drawings of a very simple voltmeter are shown in Fig.
Illustration: The Parts as They are Assembled to Make a Pocket Voltmeter for Direct Currents (Fig.
The voltmeter coil of the compensator is connected in series with the secondary coils of two transformers, which coils work against each other.
Besides the switches, already mentioned, a voltmeter and ammeter should be provided for each dynamo and also for the entire series of machines.
Both of these regulators require hand adjustment, and the attendant may employ the telephone, pressure wires, or the compensating voltmeter above mentioned, to determine the voltage at the centre of distribution.
For accurate results a step-down voltmeter transformer should be used on the testing circuit.
The voltmeter cost $7, and the ammeter $10; and the switches and fuses could be had for $5.
Turn the rheostat handle gradually; as you advance it, the voltmeter needle will advance.
You can test this fact with your own machine by cutting out the resistance from the shunt field entirely, and starting the machine slowly, increasing its speed gradually, until the voltmeter needle registers 110 volts.
In this case the voltmeter should be made to read 116 volts at the switchboard, by means of the rheostat.
If by any chance, the needle does not register, or is now back of 0, try changing about the connections or the voltmeter on the back of the switchboard.
The resistance of the voltmeter must be very high, otherwise the test must be made as in fig.
A multiplier is connected in series with the voltmeter and must be adjusted for the instrument with which it is to be used, because the resistance coil must be a multiple of the voltmeter resistance.
The voltmeter has two indices, a pointed index for close readings and an index called the normal index, which enables a slight deviation from the normal voltage to be seen from a long distance.
The error is very slight because the resistance of the voltmeter is very high and the current so small that the loss of pressure in the battery can be neglected.
What is the difference between a voltmeterand an ammeter?
A voltmeter is always connected to the two points, whose difference of potential is to be measured.
When the machine is giving the correct voltage, as indicated by the voltmeter or pilot lamp, the machine may be switched into connection with the external or working circuits.
The voltmeter is connected in parallel in the circuit at the point where the voltage is to be measured.
When thevoltmeter almost indicates zero, the brushes should be raised from contact with the commutator.
They are put up in portable boxes, and must be adjusted for each particular voltmeter as the resistance of a multiplier coil must be a multiple of the resistance of the voltmeter itself.
The time required to fully excite the field magnets is from ten to twenty seconds, the rise in field strength being indicated on the voltmeter or by the gradual increase in the brilliancy of the pilot lamp.
Showing method of connecting voltmeter to find potential difference between any two points as m and n on an electrical circuit.
The watts obtained by multiplying together the simultaneous voltmeter and ammeter readings.
By plotting the voltmeter readings and the position of the iron core on section paper, a curve is obtained showing graphically the effect of the self-induction.
In a circuit having no capacity or inductance, the power is given by the product of the respective readings of the voltmeter and ammeter, as in the case of a direct current.
This latter is simply the product of the voltmeter and ammeter readings which gives the watts just the same as in direct current.
The voltmeter V measures the pressure across the resistance XY.
It is registered by a voltmeter between B and C, less the pressure due to ohmic resistance of the inductive coil.
Join AC, which gives the impressed voltage, (that is the reading of voltmeter I in fig.
By plotting the voltmeter readings and the positions of the iron core on section paper as above, the effect of inductance is clearly shown.
Three voltmeters are required, and accordingly the method is sometimes called the three voltmeter method.
The power factor may be defined as: The number of watts indicated by a wattmeter, divided by the apparent watts, the latter being the watts as measured by a voltmeter and ammeter.
By not so much as by a vibration of the voltmeter needle, did the apparatus betray any strain as the load mounted swiftly.
VS is a voltmeter switch connecting the voltmeter with various parts of the system.
Accordingly, connections are provided to the voltmeter switch such that the attendant can compare the voltages at the dynamo terminals and bus bars before closing the dynamo switch.
Diagram showing various connections ofvoltmeter switch of the small switchboard shown in fig.
Below the voltmeter switch is a double throw switch to transfer the bus bars from connection with the dynamo switches to one with some other source of current such as a street circuit, in the event of a breakdown.
Another is that adjacent particles become charged as the plates of a minute condenser, and so are drawn tightly together as the plates in an electrostatic voltmeter are drawn towards each other.
The voltmeter is therefore the same as the ammeter, except that its dial is marked for volts instead of for amperes, and it has to be provided with the resistance coil.
Despite the fact that the voltmeter seemed to be shorted out by the relux plate, the needle pointed steadily at twenty-two.
The relux plate cooled slightly, and the voltmeter remained steady.
The voltmetergave a slight kick, then remained steady.
The row of incandescent lights is used, together with a voltmeter and an ammeter, to measure strength of current, resistance, and loss in converting.
Testing a Hewitt Converter 311 The row of incandescent lights is used, together with a voltmeter and ammeter, to measure strength of current, resistance, and loss in converting.
It is called the volt-ammeter method since it employs both a voltmeter and an ammeter.
In other words a voltmeter is connected in shunt, while an ammeter is in series with the circuit as is shown in Fig.
In place of a shunt, the voltmeteruses a coil of wire of high resistance (see R, Fig.
The high resistance of the voltmeter permits but a very small current to flow through it.
The ammeter is connected in series and the voltmeter in shunt.
Hence a voltmeter must be placed across a circuit and not in it.
In fact, a voltmeter is an ammeter which has had its shunt removed or disconnected.
What would happen if a voltmeter were put in series in a line?
Below, the master criminal could scarcely refrain from exclaiming with satisfaction as his voltmeter registered the powerful current that was passing.
Downstairs the masked master criminal had already attached a voltmeter to the wires he had installed, waiting.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "voltmeter" in a variety of sentences. We hope that you will now be able to make sentences using this word.
