K=(voltmeter range*ammeter range*power factor)/wattmeter range
You would load the circuit, and it is likely it would not operate correctly. A volt meter is designed to have a very high resistance between the two probes; an ammeter is designed to have a very low resistance. For instance, say you have a 120 watt light bulb that runs on 120 volts (you would then draw ~1 amp of current). If you tried to measure this with a meter that has .1 ohm resistance on ammeter setting, and 1,000,000 ohms on volt meter: Error due to loading: ammeter: .1 / (120 + .1) = .08%; Current will be .999Amps, power to the light bulb will be 119.9 watts Volt meter: 1,000,000/ (120 + 1,000,000) = 99.9%; current will be 120micro Amps, power to the light bulb will be 14.4 milliwatts (the light bulb will not appear to be on).
The Ammeter XD
What is the definition of voltmeter-ammeter method?
Wattmeters are used for the measurement of dielectric power loss. It is also useful for the calibration of commercial forms of wattmeter and watt-hour meter in laboratories.
The electromotive force between two points in the circuit is measured by a voltmeter. The current past any point in the circuit is measured by an ammeter inserted at that point. The resistance between any two points in the circuit is measured by an ohmmeter. The power dissipated by the circuit is measured by a wattmeter or a power meter. The energy dissipated by the circuit is measured by a watt-hour meter. The frequency of the current at a point in the circuit can be measured with an oscilloscope or a frequency counter.
So that the result that you find on the watt meter after resetting it will be accurate
1 Watt = 1 Joule / Second = 1 Newton-meter / Second.
The electrical power that you use from the utility company has to be metered. This is done with a plug in watt meter. The meter socket is what holds the electrical watt meter. It is this meter that the meter reader reads to give you your monthly billing for the electricity that you used.
A multimeter combines the functions of an ammeter, voltmeter, and ohmmeter and, so, can be used to measure current, voltage, and resistance by selecting the appropriate scale/setting.
A wattmeter is an instrument that measures the electric power of a circuit, in watts. A watt meter is installed in almost every house, and is used to determine a family's monthly electric bill.
I am assuming that you really want to use ammeters to measure power in a balanced 3 phase system. (hope you are not meaning 3 watt meter method) Power in Watt in a three phase system is equal to 1.73 x line voltage x line current x power factor. You need to know line voltage, power factor also in addition to current to compute the power. If the system is balanced then actually you do not need to connect ammeters in all three lines. One ammeter reading will do.