Electric power measuring devices
First Claim
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1. An electric power measuring device comprising:
- input means for producing first and second analogue signals respectively representative of the insntantaneous vaues of a voltage and current supplied to a load;
multiplier means for producing in response to said first and second signals a third analogue signal representative of the product of said first and second signals;
converter means for producing in response to said third signal an outputpulsel signal having a pulse rate representative of the product of said voltge and current; and
means for compensating for offset errors in said multiplier means comprising means for periodically reversing at regular intervals the polarity of one of said first and second signals at the input to said multiplier means and means effecting corresponding reversals at the input of said converter means.
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Abstract
An electric power measuring device wherein input analog signals representative of instantaneous values of current and voltage are applied to a multiplier (23) and the product applied to a converter (35, 37, 41, 43, 45, 47) to provide a pulse output signal having a frequency representative of the product and hence of the level of power consumption. Compensation for offset errors in the multiplier is effected by periodically reversing the polarity of one of the inputs to the multiplier and effecting corresponding reversals at the input to the converter to avoid irregularities in the output pulse rate when the level of power consumed is low.
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Citations
11 Claims
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1. An electric power measuring device comprising:
- input means for producing first and second analogue signals respectively representative of the insntantaneous vaues of a voltage and current supplied to a load;
multiplier means for producing in response to said first and second signals a third analogue signal representative of the product of said first and second signals;
converter means for producing in response to said third signal an outputpulsel signal having a pulse rate representative of the product of said voltge and current; and
means for compensating for offset errors in said multiplier means comprising means for periodically reversing at regular intervals the polarity of one of said first and second signals at the input to said multiplier means and means effecting corresponding reversals at the input of said converter means. - View Dependent Claims (2, 3)
- input means for producing first and second analogue signals respectively representative of the insntantaneous vaues of a voltage and current supplied to a load;
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4. An electric power measuring device comprising:
- input means for producing first and second analogue signals respectively representative of the instantaneous values of a voltage and current supplied to a load;
multipliler means for producing in response to said first and second signals al third analogue signal representative of the produce of said first and second signals;
converter meansn for producing in response to said third signal an ouput pulse signal having a pulse rate representative of the produoct of said voltage and curent; and
means for compensating for offset errors in said multiplier means comprising means for periodically reversaing at regular intervals the polarity of one of said first and second sginals at the input to said multiplier means and means effecting corresponding reversals at the inut of said convnerter means, said converter means including a capacitor and means whereby said capacitor is charged during successive charging periods of equal duration b a signal representative of said third analogue signal and by a larger reference signal, the direction of which reference signal reverses at the end of each period until the charge on the capacitor does not reverse polarity during a charging period, the direction of the reference signal being then not reversed for the next charging period to ensure a reversal of the polarity of the capacitor charge during that next period, whereafter the direction of the reference signal is again reversed at the end of each charging period. - View Dependent Claims (5, 6, 7, 8, 9, 10)
- input means for producing first and second analogue signals respectively representative of the instantaneous values of a voltage and current supplied to a load;
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11. An electric power measuring device comprising:
- input means for producing first and second analogue signals respectively representative of the instantaneous values of a voltage and current supplied to a load;
multiplier means for producing in response to said first and second signals a third analogue signal representative of the product of said first and second signals;
converter means for producing in response to said third signal an output pulse signal having a pulse rate representative of the product of said voltage and current;
means for compensating for offset errors in said multiplier means comprising means for periodically reversing at regular intervals the polarity of one of said first and second signals at the input to said multiplier means and means effecting corresponding reversals at the input of said converter means; and
inhibit means for inhibiting the output of said device unless the converter means output pulse rate exceeds a value corresponding to a predetermined value of the product of said first and second signals, said inhibit means comprising means for inhibiting the production of a pulse at the output of said device if the time which has elapsed sincne the last pulse at the output of the converter means is more than a predetermined value;
said converter means including a capacitor and means whereby said capacitor is charged during successive charging periods of equal duration by a signal representative of said third analogue signal and by a larger reerence signal, the direction of which reference signal reverses at the end of each period until the charge on the capacitor does not reverse polarity during a charging period, the direction of the reference signal being then not reversed fo the next charging period to ensure a reversal of the polarity of the capacitor charge during that next period, whereafter the direction of the reference signal is again reversed at the end of each charging period.
- input means for producing first and second analogue signals respectively representative of the instantaneous values of a voltage and current supplied to a load;
Specification