Meter (instrument)

“ So ask your printer supplier for noise figures if you think this will be a problem. Military standards say that for work needing heavy concentration—in areas like libraries and conference rooms—the sound level must be no more than 45 decibels on the dB (A) scale, which allows for sensitivity of the ear at various sound pitches. Otherwise, aim for a level less than 65 decibels. You may be able to rent the necessary meter from a scientific instrument store. Measure the sound from the distance someone’s head would be when he was working. ”

“ A small spiral spring, marked I, gives the rod a constant downward pressure, so that, when taking a measurement, the base of the tool is placed on the piece of work, and the rod always finds the bottom of the hole; then, by tightening the knurled screw F the rod is clamped in position and the tool may be picked up and its measurement read from the dial. The graduations on this instrument are similar to those of the vernier caliper, only they are much plainer, as a half-inch movement of the rod turns the dial one complete revolution. ”

“ The velocity of propagation of electric waves is the same as that of light, viz., about 1000 million feet, or 300 million metres, per second. If therefore we can measure the frequency of the oscillations in an antenna we are able to tell the wave-length emitted. Instruments for doing this are called wave meters and are of two kinds, open circuit and closed circuit. Forms of open circuit wave meter have been devised by Slaby and by Fleming. Slaby’s wave meter consists of a helix of non-insulated wire wound on a glass tube. ”

“ The meters are caused to operate by pressure on the meter key MK, associated with the answering cord as in Fig. 458. This [Page 317] increases the normal potential to 30 volts. When the armature of the meter has made a part of its stroke, it closes a contact which places its 40-ohm winding in shunt with its 500-ohm winding, thus furnishing ample power for turning the meter wheels. ”

“ After we had done so we would call it an “ammeter” because it measures amperes. Years ago people would have called it an “amperemeter” but no one who is up-to-date would call it so to-day.
If we had a very carefully made ammeter we would send it to the Bureau of Standards to be calibrated. At the Bureau they have a number of meters which they know are correct in their readings. They would put one of their meters and ours into the same circuit so that both carry the same stream of electrons as in Fig. 11. Then whatever the reading was on their meter could be marked opposite the pointer on ours. ”

“ This instrument is capable of being set to a standard measurement or of giving the actual size of a piece, and is therefore strictly speaking a combined measuring tool and a gauge. The U-shaped body of the instrument is provided with a hub a, which is threaded to receive a screw c, the latter being in one piece with the stem d, which envelops for a certain distance the hub a. The thread of c has a pitch of 40 per inch; hence one revolution of d causes the screw to move endways 1⁄40 of an inch. ”

“ This is indicated by the light moving to the end of the second division on the scale; the meter vibrates twice as fast. Now the current is three times as strong, now four times, and so on. You will observe that the position of the spot of light and the rate of vibration always correspond. Every vibration of the meter corresponds to a definite quantity of electricity, and causes a hand on a dial to move on one step. By looking at the dial, we can see how many vibrations there have been and therefore how much electricity has passed. ”

“ The fact that the iron frame of the meter lies between the permanent magnets and the current coils protects the magnets from the effects of short circuits which create a strong magnetic field within the meter itself. ”

“ A little experimenting with different windings is the easiest means of determining the proper size of wire and number of turns to meet individual requirements. After adjusting the winding so that the maximum voltage it is desired to measure produces a full-scale deflection, the scale is calibrated by marking the positions of the needle in accordance with those of the needle of a standard instrument connected in parallel with it. In marking the scale of an ammeter, connect the instruments in series. ”

“ The water-meter which is the subject of the patent consists of two parallel horizontal cylinders, each traversed by two pistons, connected together by a connecting-rod of such length that when one piston is at one end of the cylinder the other is at a sufficient distance from the other end, to leave the requisite space to be filled with the quantity of water to be measured at each stroke. ”

“ In those meters which are compounded—that is, have a shunt coil wound on the field magnets to compensate for the friction of the train—it is important to notice whether the meter will operate or continue operating when there is no current in the series coil, since a meter which “runs on the shunt” runs up a debt against the consumer for which it gives no corresponding advantage. ”

“ Such a test, is made by determining with an accurate ammeter or watt-meter the current or power supplied to a circuit for a period measured by a good clock and comparing with this the actual reading of the meter during the same time. A common source of trouble is the short circuiting of the shunt coils owing to the shellaced cotton covering of the wire becoming moist.
A good meter should start with a current which is not more than 2% of its full load current. ”

“ The principle, of the meter is to make the breaking and driving action so strong that the friction of the train becomes immaterial in comparison. This meter is an ampere-hour meter and applicable only to continuous current circuits. Another form of motor meter which is much used is that of Elihu Thomson. It takes the form of a small dynamo having an armature and field magnets without any iron core. The armature carries on its shaft a commutator made of silver slips, and the current is fed into the armature by means of brushes of silver wire. ”

“ Fig. 2. The intermediate standard decimeter a b is put in place of the mirror b; a b is a piece of cast iron, c and d are plane glass mirrors, c rests on the points of three studs, d rests on the points of three screws, c and d are made exactly parallel and the distance c d is made conveniently near to some aliquot part of the meter.
The end c is now adjusted till colored fringes appear in white light. These can be measured to within one twentieth of a wave length (probably within one-fiftieth) . ”

“ When desiring to measure a number of pieces, a standard size piece or gage is placed between the plunger B and the face L of the micrometer screw, and the instrument is adjusted until the indicator points exactly to zero on the small scale provided on the body of the micrometer. ”

“ An ammeter or ampere meter is simply a commercial form of galvanometer so constructed that the deflection of the needle indicates directly the strength of current in amperes. A good ammeter should have a very low resistance so that very little of the energy of the current will be absorbed; the needle should be dead beat, and sufficiently sensitive to respond to minute variations of current. ”

“ For this purpose a new electric current meter was invented, which consisted of a coil of wire suspended from the arm of a balance between two fixed coils (Collected Papers, i. 584) . The same principle is adopted at present in Sir William Thomson's balance instruments and in the standard Ampère meter of the Board of Trade. When using the tangent galvanometer to measure a current, an accurate value of the magnetic force due to the earth is required, and this led Joule to examine the methods ordinarily employed, and to suggest modifications and improvements. ”

“ To Send Out a 200 Meter Wave Length.--If you are using a condenser having a capacitance of .007 microfarad, which is the largest capacity value that the Government will allow an amateur to use, then if you have a hot wire ammeter in your aerial and tune the inductance coil or coils until the ammeter shows the largest amount of energy flowing through it you will know that your transmitter is tuned and that the aerial is sending out waves whose length is 200 meters. To tune to different wave lengths you must have a wave-meter. ”

“ It is easy to get a scale of 10 cms. or more to the degree, and it is not difficult with a suitable galvanometer to read to the ten-thousandth part of a degree. The length of the bridge-wire itself need not be more than 20 or 30 cms., as the balancing resistances enable the scale to be indefinitely extended. Thus the instrument possesses the great advantage over the mercury thermometer that the most open scale may be easily secured without unwieldy length, and without restricting the range of each thermometer. ”

“ In making the circuit connections, be very careful that the positive lead or wire is placed in the positive binding post of the meter. This precaution is essential for insuring an accurate and sensitive measurement on small loads. When a meter of the commutated motor type sparks at the brushes at starting, it is an indication that the commutator is dusty. Clean it with a piece of closely woven cotton tape 1/4-inch in width. [568] Meters should never be allowed to remain with their covers off, in the testing room, station, or any other place. ”

“ Consequently, when the vernier is set to the mercurial column, the difference shown by the vernier from the tenth on the scale is the hundredths to be added to the inches and tenths of the scale.
A little practice will accustom a person to set and read any barometer quickly; an important matter where accuracy is required, as the heat of the body, or the hand, is very rapidly communicated to the instrument, and may vitiate, to some extent, the observation. ”

“ When a number of instruments are in use, it is advisable to keep a standard pyrometer for checking purposes, preferably one which has been certified by the National Physical Laboratory. In conducting a test, the couples, with protecting-tubes removed, may be placed in the tube of an electric furnace of the type shown in fig. 29, in close proximity with the standard junction. On raising the temperature gradually, the readings of each working instrument may be compared with the standard, and the necessary corrections discovered. ”

“ The construction and evolution of the system of electrical units now in general use began in Europe where the metric system originated. Two of the basic units, the centimeter and the gram, are metric units; the second of time is universally employed in time measurements.
The meter, 3.2808 feet = 39.37 inches, is theoretically the one ten-millionth part of the earth’s quadrant ”

“ The tube only sounds the normal note in proportion to its length, when the diameter of the lateral opening is equal to the internal diameter of the tube at the opening. As in most of our early wood-wind instruments the holes would in that case have been too large to be stopped by the fingers, and key-mechanism was still primitive, instrument-makers resorted to the expedient of substituting a hole of smaller diameter nearer the mouthpiece for one of greater diameter in the position the hole should theoretically occupy. ”

“ The instruments have served as prototypes for the measuring instruments which have come into use in all countries, as electric power has become generally employed for domestic and commercial purposes. Ayrton and Perry also invented a clock meter and motor meter which served as models for the meters now used, and would have brought them an immense fortune, had they not abandoned their patents at too early a date. ”

“ From the neck of the bulb the glass is expanded into an oval or a cylindrical shape, to give the instrument sufficient volume for flotation; finally, it is tapered off to a narrow upright stem which encloses an ivory scale, and is closed at the top. The divisions on the scale read downward, so as to measure the length of the stem which stands above the surface of any liquid in which the hydrometer is floated. The denser the fluid, the higher will the instrument rise; the rarer, the lower it will sink. ”

“ The constant of a dynamometer may be obtained with a potentiometer, but this is usually done with precision by the manufacturer and a certificate giving the value of the constant is furnished with the instrument. ”

“ The pyrometer leads and the compensator leads are insulated and kept in place by passing through mica disks fitting the tube, which serve also to prevent convection currents up and down the tube. The protecting tube of glass or porcelain is fitted with a wooden head A carrying our insulated terminals, PP, CC, to which the pyrometer and compensator leads are respectively connected, and which serve to connect the instrument to the measuring apparatus ”

“ The piston of a water meter adapted to have an eccentric or side-rocking movement across the center of the cylinder chamber and a revolving motion, combined with a registering mechanism by means of a free or shifting connection acting with the continually changing, side-rocking movements of the piston while maintaining a driving relation with the dial mechanism. ”

“ Simpler types of electrometer of greater sensibility can however be readily constructed to give accurate results. The old type of quadrant electrometer, to be found in every laboratory, can readily be modified to prove a useful and trustworthy instrument. A light needle can be made of thin aluminium, of silvered paper or of a thin plate of mica, covered with gold-leaf to make it conducting. The aluminium wire and mirror attached should be made as light as possible. ”