Current probe
AssigneeTektronix, Inc.
InventorClifford E. Baker
Life of this patent
Estimating the term…
Abstract
A current probe comprising a Hall device and a secondary winding in a flux linking relationship with a magnetic circuit is self-calibrated by disconnecting the Hall device from the winding, passing a current through the winding so as to induce a magnetic flux in the magnetic circuit, measuring voltage developed by the Hall device in response to linking by the magnetic flux, calculating the Hall gain of the Hall device, and then adjusting the gain of a scaling output amplifier on the basis of the calculated Hall gain to compensate for variation in Hall gain due to changes in operating conditions.
Claims9
A self-calibrating current probing device having a transfer function that provides a voltage output signal in response to current flowing in a primary conductor, said current probing device comprising:
- a magnetic core in a flux linking relationship with the primary conductor, whereby flow of current in the primary conductor produces magnetic flux in the core,
- a magneto-electric converter and a secondary winding both linked by magnetic flux in the magnetic core with the magneto-electric converter coupled to a variable bias source and having a gain (K) and responsive to the magnetic flux in the magnetic core for generating an output and the secondary winding responsive to the current flow in the primary conductor,
- a power amplifier having an input selectively coupled to receive the output from the magneto-electric converter for generating a current output coupled to the secondary winding,
- an output amplifier having a termination resistor coupled in series with the secondary winding, the output amplifier having a gain of (1+E')*A.sub.s(ideal), where E' is an error factor, for producing a voltage output in response to current flowing through the termination resistor,
- a first switch having a first state in which it connects the magneto-electric converter to the power amplifier, whereby the power amplifier is responsive to the magneto-electric converter to provide an output current in response to current flowing in the primary conductor, and a second state in which the switch isolates the magneto-electric converter from the power amplifier during self-calibration of the probing device,
- a controller for generating digital codes for balancing the power amplifier, determining the gain for the output amplifier, and determining a nominal gain K.sub.nominal for the magneto-electric device as a function of the calculated error factor (E') determined by the difference between an ideal and a real transfer function for the current probing device as a fraction of the ideal transfer function for calibrating the current probing device with the balancing digital codes and the gain determining codes for the output amplifier being coupled to the input of the power amplifier via a digital-to-analog converter, and the nominal gain codes for the magneto-electric converter being coupled to the magneto-electric bias source via a digital-to-analog converter,
- a second switch coupled to receive the output developed by the magneto-electric converter, the output developed across the termination resistor, and the output voltage of the output amplifier and operative selectively to couple the respective outputs to the controller via an analog-to-digital converter for determining the balancing code for the power amplifier, the gain of the output amplifier and the nominal gain code for the magneto-electric converter.
A method of self-calibrating a current probing device having a transfer function that provides a voltage output in response to current flowing in a primary conductor, said current probing device including a magneto-electric converter and a secondary winding having N turns, both linked by magnetic flux in a magnetic core with the magneto-electric converter having a gain (K) and coupled to a variable bias source, a power amplifier connected to the magneto-electric converter and responsive thereto to provide an output current through the secondary winding, and an output amplifier having a termination resistor R.sub.t coupled in series with the secondary winding, the output amplifier producing a voltage output in response to current flowing through the termination resistor, said method comprising:
- a) disconnecting the magneto-electric converter from the power amplifier using a first switch having a first state in which it connects the magneto-electric converter to the power amplifier, whereby the power amplifier is responsive to the magneto-electric converter to provide an output current in response to current flowing in the primary conductor, and a second state in which the switch isolates the magneto-electric converter from the power amplifier during self-calibration of the probing device,
- b) applying a voltage stimulus to the variable bias source via a digital-to-analog converter coupled to a controller generating digital codes for generating a bias output to the magneto-electric converter,
- c) measuring the gain of the magneto-electric converter as a function of measuring the voltage V.sub.rt across the termination resistor R.sub.t of the output amplifier using a second switch coupled to receive the output developed across the termination resistor, the output of the output amplifier, and the output developed by the magneto-electric converter, and operative selectively to couple the respective outputs to the controller via an analog-to-digital converter, and
- d) adjusting the gain (K) of the magneto-electric converter to be equal to the nominal value K.sub.nominal thereof.
Dependencies are inferred from the claim text.