PI how to increase range?

[CatchMe]

I am using PI basic circuit only RL with clamping diodes with R before and I make an ARDUINO comparator and I start counter till the comparator signal changes, I compare the voltage from clamping diodes and compare it with pot voltage in mv. It gets 12 cm range for a metal object 10 cm 10 cm plate.

QUESTIONS:

I want to increase the range to 40 or 35 cm? what can I do?

When I use OPAMP lm318, the voltage varies from 2 volt to 4 volt, but arduino gives data than my avometer.why is that?


I have lm318 lm358 tl072 and I have 30 boost converter. I have pic12f675 with 20MHZ crystal

thanks in advance.

[Teleno]

Measures that increase range for all objects:

Earlier sampling.
achieved by:

induction balanced coil,
high bandwith amplifiers

Noise reduction
achieved by:

lower resistance values in the amplifier chain
low noise amplifiers
earlier sampling
signal averaging

For targets with long time constants.

On-time samplng

Just off the top of my head.

[F117]

Are you measuring voltage or pulse width ?
Are you sampling the voltage with a fixed delay after the TX pulse ?

I have built several detectors that measure the flyback puls width. Depending on the resolution of the timer (16 bit? - of which 10 toggle with a pulse width of 100 micros ? ) you should be able to get at least 30 cm on a 10x10 cm (iron ? ) plate.

Increasing the coil size will also get you more depth, but less sensitivity for smaller objects.


If you are measuring pulse width with a comparator ( aka temporal sampling), you might have a look at my Pickini project here:
http://www.geotech1.com/forums/showthread.php?23400-PICKINI-V4-an-easy-to-build-self-adjusting-PI-detector

[CatchMe]

I am measuring pulse width using a counter not an interrupt as there is no other routines to do[while(!comparator) counter++;].
but when i try to use ADC, it is very noisy.

when I use OPAMP it doesn't work in either methods.

And I am using a fixed time delay 5us.