- Shunted Movable Coil Ammeter, Isenthal & Co.
AMPEREMETER, or Ammeter, an instrument for the measurement of electric currents in terms of the unit called the ampere.
Another form of hot-wire ammeter is a modification of the electric thermometer originally invented by Sir W.
The capacity of the condenser is then altered until the maximum current, as indicated by a hot wire ammeter, is produced in the circuit.
A much better form of electromagnetic ammeter can be constructed on a principle now extensively employed, which consists in pivoting in the strong field of a permanent magnet a small coil through which a part of the current to be measured is sent.
A steady continuous current is then passed through the ammeter and low resistance, placed in series with one another and adjusted so as to give any required scale reading on the ammeter.
In its simplest form an electromagnetic ammeter consists of a circular coil of wire in which is pivoted eccentrically an index needle carrying at its lower end a small mass of iron.
Such an instrument is called a shunted movable coil ammeter, and is represented by a type of instrument shown in fig.
There is therefore a certain ratio in which any current passing through the ammeter is divided between the shunt and the working wire.
The ammeter to be calibrated is placed in series with a suitable low resistance which may be ï¿½i ohm, ï¿½oi ohm, ï¿½ooi ohm or more as the case may be.
The instrument therefore does not begin to read from zero current, but from some higher limit which, generally speaking, is about one-tenth of the maximum, so that an ammeter reading up to io amperes will not give much visible indication below i ampere.
If these conditions are not fulfilled sufficiently, the ammeter will not give the same indications for the same current if that current has been reached (a) by increasing from a smaller current, or (b) by decreasing from a larger current.
This can be then compared with the observed scale reading and the error of the ammeter noted.'
In this last case the shunt need not be contained in the instrument itself but may be at a considerable distance, wires being brought from the shunt which carries the main current to the movable coil ammeter itself, which performs the function simply of an indicator, 3.
- For switchboard use i n Ammeter Kelvin & electric supply stations where space is valuable, James White instruments of the type called edgewise ammeters Ltd.
Hence devices for detecting the oscillations in the antenna are merely very sensitive forms of ammeter and voltmeter.
- Diagram showing the arrangelength, and this is multiments of Hartmann and Braun's Hotplied and rendered evi- "'ire Ammeter.
Such an instrument is called a soft-iron gravity ammeter.
- Hot-wire Ammeter.
The potential difference of the ends of the low resistance is at the same time measured on the potentiometer, and the quotient of this potential difference by the known value of the low resistance gives the true value of the current passing through the ammeter.
using an ammeter is very helpful to reduce drag in any mechanism; the swing of the needle will show any tight spots.
ammeter connected in series with the appliance.
I had the ammeter made up with a 200 amp shunt, by the helpful people at Adverc Ltd.
A shunt is resistive device used to generate a small signal voltage to display current on a moving coil ammeter.
ammeter in series to monitor the exact current.
Immediately on my return from Great Britain, I sent the unrestored ammeter for restoration to Vintage Restorations.
Finally the fuses were put in and we checked the digital ammeter on the control unit.
The ammeter to be calibrated is placed in series with a suitable low resistance which may be Ã¯¿½i ohm, Ã¯¿½oi ohm, Ã¯¿½ooi ohm or more as the case may be.
A good ammeter should comply with the following qualifications: - (i) its readings should be the same for the same current whether reached by increasing from a lower current or decreasing from a higher current; (2) if used for alternating currents its indications should not vary with the frequency within the range of frequency for which it is likely to be used; (3) it should not be disturbed by external magnetic fields; (4) the scale divisions should, if possible, be equal in length and there should be no dead part in the scale.
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 2 See Journ.
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