Some questions about ultrasonic probe driving / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Some questions about ultrasonic probe driving

1 2 next

Move Thread

LAN_403

TheMerovingian

Sat Dec 11 2010, 12:11AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

I'm trying to design an ultrasonic rangefinder and I'm using the matching transformer topology.

the questions are:
1) THe oscillation frequency is determined by the tank circuit (secondary inductance, ultrasonic probe capacitance) ? I ask you that because I probably mis-designed the transformer; according to my scope the oscillation freq is 30KHz (i need 40KHz to correctly detect the echo) 80Vp-p (i need 140Vp-p). If the answer is yes, i will reduce secondary turns from 500 to 370 (primary turns will be reduced too)
2) The transformer can have air gaps or it is deleterious?

Thank you in advance

Steve Conner

Sat Dec 11 2010, 03:21PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes, the transformer probably should have an air gap to stabilise the inductance. But you need to be sure which inductance it is that's tuning your transducer- is it the magnetizing inductance or the leakage inductance? The air gap has no effect on the latter.

TheMerovingian

Sat Dec 11 2010, 11:53PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

According to my o-scope now the tank frequency is 35.7KHz, still too low, the peak to peak voltage is 120Vp-p . I adjusted the pic square wave for perfect resonance, getting those results. THe disappointing thing is that the transduced cannot detect any echo, so the point is: it is a 40KHz unit, running it out of resonance does not allow echo detection (preamplification by the mechanical-electrical resonance), or the unit is defective. I will reduce secondary turns again to get perfect 40KHz and i'm goint to see what happens.

Here's a pic of the oscope waveforms:

Channel 1: Transducer voltage waveforms
Channel 2: Driving waveform (PIC)

Sulaiman

Sun Dec 12 2010, 08:29AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

The first thing I'd do is measure the resonant frequency of the receiver.(sig.gen,/resistor/'scope) and transmitter piezo elements,
to check they both work and have a similar resonant frequency.

Larger industrial/commercial ultrasonic rangefinders that I have repaired (3" to 10" diameter transducer) used a step-up transformer with variable output taps and an inductor with variable taps in series with the output. So I guess there's quite a bit of variation in resonant frequency and efficiency lot-to-lot.
Industrial units use the same transducer for Transmit & Receive.

Conundrum

Sun Dec 12 2010, 01:46PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

if its any help, i just fitted one on my car.

the transducer seems to send out pulse trains about 10 times a second (can feel them on a finger held near it)

-A

TheMerovingian

Sun Dec 12 2010, 04:10PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Sulaiman wrote ...

The first thing I'd do is measure the resonant frequency of the receiver.(sig.gen,/resistor/'scope) and transmitter piezo elements,
to check they both work and have a similar resonant frequency.

Larger industrial/commercial ultrasonic rangefinders that I have repaired (3" to 10" diameter transducer) used a step-up transformer with variable output taps and an inductor with variable taps in series with the output. So I guess there's quite a bit of variation in resonant frequency and efficiency lot-to-lot.
Industrial units use the same transducer for Transmit & Receive.

THe transmitter works also like a receiver and the datasheet says that the resonamce frequency is 40Khz

radiotech

Sun Dec 12 2010, 11:02PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

"secondary inductance, ultrasonic probe capacitance"

Things that move with applied voltage probably have a
'motional impedance' that your resonant driver has to
include.

Could you measure the voltage on one scope channel and
current on the other and try and determine a good
figure for the impedance in terms of reactance and resistance?

You might take a peek at the boaters' sonar/fish locators
which work about that frequency and have simple transponder
circuits

TheMerovingian

Sun Dec 12 2010, 11:08PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

I tried to adjust secondary inductance (and primary also). THe resonance is close to 42Khz 130Vp-p sinusoidal but no echo is detected, i feel a "snap" each pulse on my finger when i touch the probe. It is close to the 40Khz but no echo is detected, even setting my scope to 10mV per division.

I have detected an echo, but is it very low level, some around 4-10mVp-p at with target at 60cm, moving it gave exactly the distance after calculations. I hope that when it will be tuned the echo will have higher voltage

radiotech

Mon Dec 13 2010, 08:00AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

i feel a "snap" each pulse on my finger when i touch the probe.

People have told me they like to keep far away from live sonar
transducers, so this is probably a habit to lose.

Steve Conner

Mon Dec 13 2010, 11:23AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

TheMerovingian wrote ...

I have detected an echo, but is it very low level, some around 4-10mVp-p at with target at 60cm,

Seems like quite a reasonable voltage, what makes you think it should be higher?

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob