Patent ID: 7212930

Claim:
A power meter comprising: (a) a trigger amplitude detector sensing a supply voltage, said trigger amplitude detector outputting a signal to initiate measurement of a first interval when an amplitude of said supply voltage exceeds a trigger amplitude and outputting another signal to terminate measurement of said first interval when said amplitude of said supply voltage no longer exceeds said trigger voltage; and (b) a data processing system arranged to periodically sample a load current and including an instruction to: (i) compare an amplitude of a present load current sample to an amplitude of a previous load current sample; (ii) initiate measurement of a second interval upon the earlier occurrence of: (a) initiation of said measurement of said first interval; and (b) said amplitude of said present load current sample not exceeding said amplitude of said previous load current sample; (iii) terminating measurement of said second interval upon the later occurrence of: (a) said amplitude of said first load current sample not exceeding said amplitude of said previous load current sample; and (b) termination of said measurement of said first interval; and (c) calculating a relative phase angle of said supply voltage and said load current from said first and said second intervals.