Dual-range measurement of electrical current
View Patent ↗An electrical current measurement system. A sense impedance and a composite amplifier are in electrical communication and together define a trans-impedance circuit that presents a frequency-compensated impedance lower than the sense impedance to an input electrical current to be measured. A sense amplifier in electrical communication with the sense impedance provides an output indicative of a magnitude of the input electrical current. A current bypass circuit may parallel the trans-impedance circuit and bypass the input electrical current around the trans-impedance circuit when the current reaches a predefined magnitude. The system may be combined with another current sensor to form a dual-range current measurement instrument.
1. An electrical current measurement system comprising:
a sense impedance;
a composite amplifier in electrical communication with the sense impedance, the sense impedance and the composite amplifier together defining a trans-impedance circuit operative to present a frequency-compensated impedance to an input electrical current to be measured, the frequency-compensated impedance being lower than the sense impedance; and
a sense amplifier in electrical communication with the sense impedance and operative to provide an output indicative of a magnitude of the input electrical current.
2. A system as in claim 1 wherein the sense impedance and the composite amplifier are in a series configuration.
3. A system as in claim 1 wherein the frequency-compensated impedance simulates an inductive load over at least a portion of its frequency range.
4. A system as in claim 1 wherein the sense impedance comprises a resistor and a capacitor in a parallel configuration.
5. A system as in claim 1 wherein the sense amplifier comprises an instrumentation amplifier.
6. A system as in claim 1 and further comprising a bypass capacitor in parallel with the trans-impedance circuit.
7. An electrical current measurement system comprising:
a sense impedance;
a composite amplifier in electrical communication with the sense impedance, the sense impedance and the composite amplifier together defining a trans-impedance circuit operative to present a frequency-compensated impedance to an input electrical current to be measured, the frequency-compensated impedance being lower than the sense impedance;
a sense amplifier in electrical communication with the sense impedance and operative to provide an output indicative of a magnitude of the input electrical current; and
a current bypass circuit in parallel connection with and responsive to the trans-impedance circuit to bypass the input electrical current through a bypass path around the trans-impedance circuit when the current reaches a predefined magnitude.
8. A system as in claim 7 wherein the bypass path comprises complementary field effect transistors in a parallel configuration.
9. A system as in claim 7 and further comprising a switching element operative when activated to disable the trans-impedance circuit.
10. A system as in claim 9 wherein the switching element comprises a normally-closed switch in series connection with the sense impedance.
11. A system as in claim 9 wherein the current bypass circuit comprises a timing circuit and wherein the switching element is operative when activated to apply a bias to the current bypass circuit through the timing circuit and thereby activate the current bypass circuit at a controlled rate.
12. A dual-range current measurement system comprising:
a high-current sense impedance connected to receive an electrical current to be measured;
a high-range sense amplifier, in electrical communication with the high-current sense impedance and operative to provide an output indicative of a magnitude of the electrical current within a relatively high range of values;
a trans-impedance circuit connected to receive the electrical current, the trans-impedance circuit including a low-current sense impedance and a composite amplifier in electrical communication, the trans-impedance circuit operative to present a frequency-compensated impedance to the electrical current, the frequency-compensated impedance being lower than the sense impedance;
a low-range sense amplifier, in electrical communication with the low-current sense impedance and operative to provide an output indicative of a magnitude of the electrical current within a relatively low range of values; and
a current bypass circuit in parallel connection with the trans-impedance circuit, operative to conduct the electrical current when the current exceeds the low range of values.
13. A system as in claim 12 wherein the sense impedance and the composite amplifier are in a series configuration.
14. A system as in claim 12 wherein the frequency-compensated impedance simulates an inductive load over at least a portion of its frequency range.
15. A system as in claim 12 wherein the high-current sense impedance comprises a resistor and a capacitor in parallel connection and the low-current sense impedance comprises a resistor and a capacitor in parallel connection.
16. A system as in claim 12 wherein the current bypass circuit comprises complementary field effect transistors in a parallel configuration.
17. A system as in claim 12 wherein each sense amplifier comprises an instrumentation amplifier.
18. A system as in claim 12 and further comprising a switching element operative when activated to disable the trans-impedance circuit, the switching element comprising a normally-closed switch in series connection with a current path through the low-range sense impedance.
19. A system as in claim 12 wherein the current bypass circuit comprises a timing circuit and further comprising a switching element operative when activated to apply a bias to the current bypass circuit through the timing circuit and thereby activate the current bypass circuit at a controlled rate.
20. A system as in claim 12 and further comprising a bypass capacitor in parallel with the trans-impedance circuit and the current bypass circuit.