Ammeters sentence example
- Like the corresponding ammeters, they have the great advantage that the scales are equidivisional and that there is no dead part in the scale, whereas both the electrostatic and electrothermal voltmeters, above described, labour under the disadvantage that the scale divisions are not equal but increase with rise of voltages, hence there is generally a portion of the scale near the zero point where the divisions are so close as to be useless for reading purposes and are therefore omitted.
- Until they received them they were using huge old wooden voltmeters and ammeters from the 1950s. or at least the ones that still worked.
- Hence we may classify ammeters into (1) Thermal; (2) Electromagnetic, and (3) Electrodynamic instruments.
- The instrument then simply becomes an am meter of high resistance, and may take any of the forms of practically used ammeters (see Amperemeter).
- Ammeters to measure the volume, and voltmeters to determine the pressure of current supplied to the baths, should also be provided.Advertisement
- From this it follows that hot-wire ammeters are generally not capable of giving visible indications below a certain minimum current for each instrument.
- In the case of ammeters intended for very small currents, the whole current can be sent through the coil, but for larger currents it is necessary to provide in the instrument a shunt which carries the main current, the movable coil being connected to the ends of this shunt so that it takes a definite small fraction of the current passed through the instrument.
- In ammeters for small currents it is customary to pass the whole current through the heating wire.
- The calibration of ammeters is best conducted by means of a series of standard low resistances and of a potentio meter.
- Hot-wire ammeters are, however, liable to a shift of zero, and means are always provided by some adjusting screw for slightly altering the sag of the wire and so adjusting the index needle to the zero of the scale.Advertisement
- In the use of ammeters in which the control is the gravity of a weight, such as the Kelvin ampere balances and other instruments, it should be noted that the scale reading or indication of the instrument will vary with the latitude and with the height of the instrument above the mean sea-level.
- Direct reading equidivisional movable coil ammeters can be made in various portable forms, and are very much employed as laboratory instruments and also as ammeters for the measurement of large electric currents in electric generating stations.