Electrodynamometer instrument as a wattmeter: [ alt="F1 U.B M.P 13.08.19 D 4" src="//storage.googleapis.com/tb-img/production/19/08/F1_U.B_M.P_13.08.19_D%204.png" style="width: 314px; height: 184px;"> An electrodynamometer instrument can be used as a wattmeter to measure power and frequency. An electrodynamometer instrument can be used for both a.c. and d.c. quantities. Two fixed coils are connected in series with the load are called current coils; These will carry a full load current IL as shown in the figure The moving coil is connected across the supply is called a voltage coil (or) pressure coil, which will carry a current IP as shown in the figure Both coils are connected in parallel so that two different currents will flow through the coils IL and IP respectively [ alt="26 June 1" src="//storage.googleapis.com/tb-img/production/19/08/26%20June_1.png" style="width: 160px; height: 46px;"> Moving Iron (MI) type instruments can be used for both AC & DC measurements. But Moving Iron connected through current Transformer block DC supply. So that Moving Iron connected through current Transformer is only used for AC measurements. Rectifier type instruments are used for both AC & DC measurements. Induction type instruments are only used for AC measurements. Permanent Magnet Moving Coil (PMMC) is only used for DC measurements.