Pulsed coil drive circuit for a sampled inductive transducer
A pulsed coil drive for a sampled inductive transducer has at least one drive coil connected in a series circuit with a capacitor having a first terminal connected to the negative terminal of a voltage source. The series circuit is normally open during the intervals between pulses. Sampling occurs once per pulse. Each pulse's sampling interval is preceded by a pre-sampling interval and followed by a post-sampling interval. The supply voltage that is applied across the series circuit during both the pre- and post-sampling intervals is applied by switching a first terminal of the coil's free terminal to the voltage source's positive terminal through a p-channel MOSFET. During the sampling interval, the series circuit is shorted by switching the coil's free terminal to the voltage source's negative terminal through an n-channel MOSFET.
1. A pulsed coil drive for a sampled inductive transducer wherein at least one drive coil and a capacitor form a series circuit that is open during intervals between pulses, each pulse having three successive sampling intervals, a pre-sampling interval with a first voltage switched across the series circuit, a sampling interval with a second voltage switched across the series circuit long enough for adequate sampling, and a post-sampling interval with the first voltage switched across the series circuit.
2. The pulsed coil drive according to claim 1 , wherein the post-sampling interval is shorter than the pre-sampling interval, so as to have negligible current through the series circuit at the end of the pulse.
3. The pulsed coil drive according to claim 1 , including a switch through which the first voltage is applied to the series circuit and a diode shunting the switch and which turns on when the voltage across the series circuit has the same polarity and is higher than the first voltage.
4. The pulsed coil drive according to claim 1 , wherein the capacitor has a free end connected to one terminal of a voltage source, the at least one drive coil has a free end, left open between pulses and switched to the other terminal of the voltage source or first voltage during the pre-sampling interval, is then switched to the one terminal of the voltage source during the sampling interval, the second voltage being thus zero, and then switched back to the other terminal of the voltage source or first voltage during the post-sampling interval, and left open at the end of the pulse.
5. The pulsed coil drive according to claim 4 wherein the capacitor's free end is connected to the negative terminal of a voltage source, the at least one drive coil's free end, left open between pulses, is switched to the positive terminal of the voltage source through a p-channel MOSFET during the pre-sampling and post-sampling intervals, and switched to the negative terminal of the voltage source through an n-channels MOSFET switch during the sampling interval, the pre-and post-sampling intervals together being shorter than the sampling interval.
6. The pulsed coil drive according to claim 1 , wherein the sampled inductive transducer includes two or more coils, each coil having one of its terminals connected the capacitor, the other terminal being either left open or selected to form a series circuit with the capacitor for the duration of at least one entire pulse.