I’m a complete newbie when it comes to designing my own electronics so I need some help.

What I would like to achieve is some electronics to take a reading off say a 0-5v sensor and then use a feedback loop to maintain a set reading off the sensor by controlling the voltage of some 230v ac motors.

The actual logic would be very similar to that driving your narrowband o2 sensor.

My biggest question is what is the bit of kit with inputs and outputs that I program this logic into and how?

It may helkp if you can say a few words what you are tying to achieve rather than asking for a circuit that you perceive as the solution.

Sounds like you want some speed controller perhaps see here

Also are you looking for an analogue soltuion or digital one involving a microcontroller.

It'd help if you explain the process better.

IE does the speed of the AC motors directly effect the sensor signal (ie a full feedback system) or is the sensor signal just be used to control the AC signal.
If the motor speed directly controls the signal you can use a full feedback loop (likely analogue) otherwise you're looking at a look-up table (likely digital solution).

Too many unknowns here.

It sounds like a speed controller driven by a signal from a sensor related to engine speed or some other feedback based system.

It sounds as if the best bet would be a three phase motor driven by an inverter, this could then be driven by a 0-10v 0r 4 t0 20ma signal derived from a sensor and signal conditioner, or it may be possible to find an inverter that can take a sensor input direct a bitlike a servo drive.
Paul.

What kind of motor do you need to control? A 3 phase motor will need a variable frequency drive to control speed, a single phase induction motor can use variable frequency or phase angle, and a universal motor (one with brushes and commutator) requires variable voltage (including phase control) to control speed.

Is the sensor a hall effect sensor to measure rotational speed?

[Edited on 14/1/09 by MikeRJ]

What you are trying to achieve requires you have a basic (at least) understanding of control theory and specifically PID loops.

It's very easy for the feedback loop to induce major oscillations and resonances.

I've seen simple, machines try to shake themselves to pieces when the thing isn't correctly tuned.