Circuit for measurement of electrical pollution on power line
A circuit and method for measuring pollution on an AC power line is described. After attenuation of the AC power signal, the remaining signal is differentiated, rectified and smoothed to provide a DC signal representative of the pollution which can be viewed on an ordinary meter.
1. A circuit for use in measuring pollution on a power line comprising:
a filter for attenuating a power line signal, coupled to the power line;
a differentiator coupled to the filter;
an amplifier having an input coupled to the differentiator; and
a feedback path coupled between an output of the amplifier and its input having a parallel, coupled resistor and capacitor for averaging the output of the amplifier and a rectifier, such that the output of the amplifier is a DC signal.
2. The circuit defined by claim 1 , wherein the differentiator is a capacitor.
3. The circuit defined by claim 1 , including input protection coupled at the input to the amplifier.
4. The circuit defined by claim 3 , wherein the input protection comprises parallel diodes with their polarities reversed.
5. The circuit defined by claim 1 , wherein the amplifier is an OP amplifier.
6. The circuit defined by claim 5 , wherein the feedback path is coupled between the output of the OP amplifier, and a negative input terminal of the OP amp.
7. The circuit defined by claim 1 , including a meter coupled to the output of the amplifier.
8. The circuit defined by claim 1 , including means for providing a perceptible indication of the DC signal at the output of the amplifier.
9. The circuit defined by claim 8 , including a voltage divider for reducing the line voltage before it is coupled to the filter.
10. The circuit defined by claim 1 , including a meter coupled to the output of the amplifier, the meter including a battery having a pair of terminals, the pair of terminals being coupled to power the amplifier, one of the terminals being capacitively coupled to a ground common with a line of the power line signal.
11. A circuit for use in measuring pollution on a power line comprising:
a filter for attenuating the fundamental frequency of the power line signal;
a capacitor coupled to the filter for differentiating the output signal from the filter;
an operational amplifier (OP amp) having a negative terminal coupled to the capacitor, an output of the OP amp being coupled to the negative terminal of the OP amp through a feedback path which includes a rectifier and a parallel combination of a resistor and a capacitor having an RC time constant, the RC time constant and rectifier to cause the output of the OP amp to be a DC signal.
12. The circuit defined by claim 11 , including a voltage divider for reducing the AC line potential before it is coupled to the filter.
13. The circuit defined by claim 12 , including a pair of parallel diodes connected with their polarities reversed disposed between the negative terminal and a positive terminal of the OP amp for limiting the amplitude of the signal applied to the OP amp.
14. The circuit defined by claim 13 , including a meter coupled to the output of the OP amp.
15. A method for measuring pollution on a power line comprising:
sensing a power line signal and a polluting signal on the power line;
attenuating the sensed power line signal;
differentiating the signal remaining from the attenuation;
averaging the differentiated signal so as to obtain a signal representative of the pollution of the power line; and
displaying the averaged signal.