power factor measurement
According to DIN 40110 " Alternating current quantities", the power factor or effective factor (cos phi) is the quotient of active power (P) and apparent power (S); i.e. Cos phi = P/S.
It can be measured with electrodynamic quotient meters or indirectly via current, voltage and active power. Measuring devices for connection in three- phase networks are also common.
The measuring methods with quotient meters are error-prone and have recently been replaced by digital multimeters, which provide a direct indication of active power, reactive power (Q) and cosine 'phi'. They have a high internal resistance of 10 mega-ohms in the voltage path.