linear solenoid control and inducer feedback

[Rx7man]

I'm working on a project for a diesel injection pump control, it has 2 large solenoids to control fuel quantity and timing, 1 variable reluctance (VR) sensor coil that triggers at a specific engine location, and one VR/Eddy current sensor coil that somehow gives feedback for the fuel quantity.. that's the one I really need help with

Here's an overview, at the top is the timing solenoid, center is the fuel solenoid (moves toward camera when energized), then there are the 2 VR sensor coils on the right, the part facing the camera is for fuel position, the one facing down toward the connector (hard to see) is for engine timing   Sorry, I don't seem to be able to attach the images where they're supposed to be


Closeup of VR sensors


the engine timing VR sensor picks up on this little tit, with a zero crossing detector this should be no problem to interface (Max9924 or similar)



Here are the pump side actuated components, the top lever is rotate by the timing solenoid, it has no feedback, while the fuel metering part slides in and out and has the square copper ring attached to it, this slides along the "stem" of the sensor (the ring is non magnetic, so I figure it's pure copper)... I'm not even sure on the exact terminology for this kind of sensor, Eddy current seems to be the closest thing I could find, though they seem to be used a little differently in the examples I've found


How do you suggest implementing something that can sense the position of this copper ring on the coil's stem? I'm sure in the OEM application it's capable of determining position to within 0.1mm, and it shouldn't drift while being operated



I'll also have to make a driver for the solenoids and have a current sense circuit on them
Here's my measurements on the specs of each coil.. mind you on the low ohm range I don't trust my cheap meter
Fuel solenoid - 1 ohm, 5mH
Timing solenoid - 2 ohm 10mH
Timing VR sense coil 25ohm 37mH
Fuel position VR sense coil 25 ohm 25mH

[Rx7man]

Alright, I've been playing with it a bit, I fed the coil a sine wave from a function generator through a resistor, and then watched the waveform on my scope, I got the highest amplitude waveform when I fed it around 75khz, which I guess is the resonant frequency of the circuit... at this frequency I was able to see a very clear change when I put the copper loop over the sensor, peak-to-peak voltage went from 1.7V down to 0.7 volt, but I didn't see any phase or frequency shift I was expecting.. I guess maybe I can implement this with a 555 timer, rectify the output into an op-amp and filter it for peaks, then feed it to an analog pin on the microcontroller.
Does that sound like a reasonable way to do it?

[Terry Bites]

What circuit would that be?

[Rx7man]

What circuit would that be?

I'm looking at this circuit http://www.learningaboutelectronics.com/Articles/Sine-wave-generator-circuit-with-a-555-timer.php, though after trying to model it in spice I think I might have to put it through an amplifier to keep the output frequency stable with varying output impedences