# Induction meter, finding standard reading

If I have the time it takes an induction meters disc to complete one revolution, then how can I work out the power in watts ?, I feel like i'm missing some other parameter that is needed

I basically have a three phase system with three check wattmeters and an induction meter and am told to find the error of the induction meter by comparing it to the wattmeter readings

Also, Am I right in saying the wattmeters measure real power ?, example, for 0.8 lagging pf, the wattmeter reading would be VI*0.8 ?

And does the induction meter measure apparent power or real power only ?

• Photos of the meters, please, showing the details on the front which should include the kWh and kVArh per revolution. Commented Sep 26, 2016 at 20:14
• Kh is USUALLY either 1000 rotations per kWh or 3600 rotations Commented Sep 27, 2016 at 2:56

You are missing the meter rating of Kh

Kh is given in units of watt-hours per revolution.

• e.g. 7.2 Wh/rev or ~26 kW-s/rev
• then divide 7.2 by fraction of hour/rev
-or divide 26 kW-s/rev by seconds per rev
• this gives true power in kW for an Induction meter based on calibrated eddy current Induction motor torque

First of all remember the induction meter is registering the energy supplied. Not the power. The energy is expressed as power * time. One revolution of the disk is an indication of the amount of energy supplied. On the meter front you will find information of the amount of energy supplied per revolution or in the case of this picture the number of revolutions per kW-h. Or on the GE meter the Kh value used in the other answer. When you have a 3 phase meter then there are three disks all linked together on one shaft with one registration counter.

Since there are separate coils in the meter for measuring the voltages and the currents. The influence of the power factor (PF) is automatically taken into account.

The disk(s) in the meter turn due to the eddycurrent induced by combination of the voltage and current coil. If only the voltage is present there is no rotating field and the disk does not turn.For only the current the same principle.

Based on the above principles the meter indicates the real amount of energy, not power, supplied.

Some meters have more than one counter. The are then used for e.g. day and night. The change from one counter to the other counter can be done with a local clock or remote by an incomming high frequency signal.