Intelligent electronic device with broad-range high accuracy
View Patent ↗A method and apparatus provides high-accuracy measurements of an electrical parameter across a broad range of parameter input values. In one embodiment, an intelligent electronic device (IED), e.g., a digital electrical power and energy meter, with a plurality of independently-adjustable gain factors measures a parameter, and calculates and stores calibration factors associated with known values of the measured parameter. The IED or meter applies the stored calibration factors when measuring unknown values of the measured parameter, to improve the accuracy of the measurement.
1. An intelligent electronic device comprising:
a sensing circuit having one or more sensors for sensing at least one parameter of an AC electrical service, each of the one or more sensors generating a first signal representative of the sensed parameter;
a plurality of gain-adjustable channels, each channel having at least one gain adjustment circuit for individually adjusting a gain factor and each channel comprising at least one first signal generated by the one or more sensors, the at least one first signal representative of the sensed parameter;
one or more computer-readable storage devices;
a plurality of calibration factors stored in the one or more computer-readable storage devices, the plurality of calibration factors corresponding to a plurality of calibration measurements, the plurality of calibration measurements comprising measurements of a second signal representative of a known value of the parameter at a plurality of signal amplitudes in each of a plurality of calibration ranges; and
a processor that determines a calibrated value for a measured data point using interpolation of the results of the plurality of calibration measurements.
2. The intelligent electronic device of claim 1 , wherein the processor determines at least one additional calibration factor for the measured data point by interpolating two calibration factors, each of the two calibration factors corresponding to a calibration measurement adjacent to the measured data point.
3. The intelligent electronic device of claim 1 , wherein the processor determines the at least one additional calibration factor for the measured data point by determining a slope of a line between two calibration factors corresponding to a calibration measurement adjacent to the measured data point.
4. The intelligent electronic device of claim 3 , wherein the slope b is determined by the equation:
b
=
(
F
2
-
F
1
)
(
X
M
2
-
X
M
1
)
where F 1 is a first adjacent calibration factor, F 2 is a second adjacent calibration factor, X M1 is a first adjacent calibration measurement and X M2 is a second adjacent calibration measurement.
5. The intelligent electronic device of claim 4 , wherein the at least one additional calibration factor F 3 is determined by the equation:
F 3 =( X M3 −X M2 ) b+F 2
where F 2 is the second adjacent calibration factor, X M2 is the second adjacent calibration measurement, b is the slope and X M3 is the measured data point.
6. The intelligent electronic device of claim 5 , wherein the processor applies the at least one additional calibration factor F 3 to the measured data point.
7. The intelligent electronic device of claim 5 , wherein the processor stores the at least one additional calibration factor F 3 in the one or more computer-readable storage devices.
8. The intelligent electronic device of claim 1 , wherein the second signal representative of a known value is representative of one of a known voltage and a known current and wherein the plurality of calibration ranges includes 69 V, 120 V, 220 V, and 480 V for second signals representative of a known voltage, and 250 mA, 500 mA, 1 A, and 5 A for second signals representative of a known current.
9. The intelligent electronic device of claim 1 , wherein the plurality of calibration measurements further comprises measurements of the second signal representative of the known value of the parameter at a plurality of known signal frequencies.
10. The intelligent electronic device of claim 9 , wherein the plurality of known signal frequencies includes 50 Hz and 60 Hz.
11. The intelligent electronic device of claim 1 , wherein the processor determines the calibrated value for the measured data point by interpolating two calibration measurements, each of the two calibration measurements taken adjacent to the measured data point.
12. The intelligent electronic device of claim 1 , wherein the processor determines the calibrated value for the measured data point by determining a slope of a line between two actual measurement values corresponding to two calibration measurements adjacent to the measured data point.
13. The intelligent electronic device of claim 12 , wherein the slope b is determined by the equation:
b
=
(
X
A
2
-
X
A
1
)
(
X
M
2
-
X
M
1
)
where X A1 is a first actual measurement value, X A2 is a second actual measurement value, X M1 is a first calibration measurement and X M2 is a second calibration measurement.
14. The intelligent electronic device of claim 13 , wherein the calibrated value of the measured data point X A3 is determined by the equation:
X A3 =( X M3 −X M2 ) b+X A2
where X A2 is the second actual measured value, X M2 is the second calibration measurement, b is the slope and X M3 is the measured data point.
15. The intelligent electronic device of claim 14 , wherein the processor stores the calibrated value of the measured data point X A3 in the one or more computer-readable storage devices.
16. A method for calibrating a digital power and energy meter, the method comprising:
providing a plurality of signals in each of a plurality of calibration ranges, each of the plurality of signals comprising one of a known voltage signal or a known current signal;
taking a measurement, at each of a plurality of signal amplitudes, of each of the plurality of signals using the digital power and energy meter;
comparing, for each measurement, the measured value of the known voltage signal or the known current signal to the actual value of the known voltage signal or the known current signal;
determining, for each measurement, a corresponding calibration factor;
storing the plurality of calibration factors in a computer-readable storage device, to allow the digital power and energy meter to apply a corresponding one of the plurality of calibration factors in response to a measurement of an unknown voltage signal or an unknown current signal to determine the value of the unknown voltage signal or the unknown current signal with at least a pre-determined level of accuracy; and
determining at least one additional calibration factor using interpolation of the stored calibration factors.
17. The method of claim 16 , further comprising determining at least one additional calibration factor for a measured data point by determining a slope of a line between two calibration factors corresponding to a calibration measurement adjacent to the measured data point.
18. The method of claim 17 , wherein the slope b is determined by the equation:
b
=
(
F
2
-
F
1
)
(
X
M
2
-
X
M
1
)
where F 1 is a first adjacent calibration factor, F 2 is a second adjacent calibration factor, X M1 is a first adjacent calibration measurement and X M2 is a second adjacent calibration measurement.
19. The method of claim 18 , wherein the at least one additional calibration factor F 3 is determined by the equation:
F 3 =( X M3 −X M2 ) b+F 2
where F 2 is the second adjacent calibration factor, X M2 is the second adjacent calibration measurement, b is the slope and X M3 is the measured data point.
20. The method of claim 19 , further comprising storing the at least one additional calibration factor F 3 in the computer-readable storage device.
21. An intelligent electronic device comprising:
a sensing circuit having one or more sensors for sensing at least one parameter of an AC electrical service, each of the one or more sensors generating a first signal representative of the sensed parameter;
a plurality of gain-adjustable channels, each channel having at least one gain adjustment circuit for individually adjusting a gain factor and each channel comprising at least one first signal generated by the one or more sensors, the at least one first signal representative of the sensed parameter;
one or more computer-readable storage devices;
a plurality of calibration factors stored in the one or more computer-readable storage devices, the plurality of calibration factors corresponding to a plurality of calibration measurements, the plurality of calibration measurements comprising measurements of a second signal representative of a known value of the parameter at a plurality of signal amplitudes in each of a plurality of calibration ranges; and
a processor that determines at least one additional calibration factor using interpolation of the results of the plurality of calibration measurements.