Calibrating an Ammeter is a broad statement, because the Ammeter can be AC or DC. The current ranges can be in uA, or mA, or Amp or a few hundred amperes. So there appears to be a wide variety of ranges in current measurement. Since the measurement philosophy is same for any current meter measurement, a DC ammeter is studied for experimental purpose in this experimental setup. Any moving coil meter is a current meter. Normally it is designed to deflect the needle for 100 or 200?A FSD depending on the coil resistance used in the meter. This resistance can be called as INTERNAL RESISTANCE OF THE METER. However in reality any electrical or electronic circuits do provide much more current than 100 or 200?A in their circuits, typically anywhere between 1mA to a few Amperes. Therefore any current meter that we use in the laboratory do not have this capability. Therefore some extra elements are added to make it appear as though the current meter really reads what we see in the laboratory. Kirchoffs current law will yield better explanation how this is achieved. Calibrating an ammeter is a two step approach. An ammeter is said, to have been calibrated, if it can be tested for a) accuracy of the basic meter with 100?A FSD or
b) If it is calibrated and displayed on the scale of the meter, for functional applications, like displaying any other parameter with engineering units like A, RPM, Kg/Cm2 or 0C etc. In this trainer, all the facilities required to calibrate an Ammeter is attempted. While doing so, the above tasks are studied for experimental purposes. Specifications:
Analog Ammeter : Moving coil type
Range : 25mA DC FSD
Digital meter : 3-? digit digital Ammeter
Range : 20mA DC FSD
Input voltage source : 5 V DC Fixed
Load resistor : A continuously variable load resistance in the range of 100 to
5 K Ohms using potentiometer method.
Shunt resistor : 10K Ohm shunt resistor will be supplied.
Power supply : Necessary built-in power supplies operating at 230V AC mains.
Cabinet : An ergonomically designed cabinet |
