Crowbar-style post-pulse loading of transducers does help but not enough to write home about. At the end of the day the bandwidth of the transducer is what it is. Or as the old mediterranean farmers would say, que sera sera.
Those are the most fun project, where visitors would say "What on earth is THAT?"
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is
Maybe a hybrid of sorts where you slap on some zener clamps, then actively damp the transducer when the voltage is acceptable. After a while, it just gets simpler to give the customer what they asked for in the first place.
I often wonder how many little Skunkworks there are dotted across the country. I think I posted here before about the Varian skunkworks located in some industrial park in Sunnyvale. They were designing the first ion implanter off premises to keep it secret. It was shielded poorly and could deflect the CRTs in nearby TV sets.
This particular skunkworks I was in was an unfinished floor of a mid- rise building. The air ducts and all the hangers were exposed. In theory, it would not pass an occupancy permit inspection.
It really doesn't buy much. The ringdown performance of a transducer is mostly concentrating on the backing material. This is also why that stuff is as closely guarded a secret as the Coca Cola recipe was.
Most skunkworks are in small to very small companies. Usually in stealth mode like some of my clients. This is also why I can rarely state references because they do not want any exposure whatsoever unless absolutely needed (like when dealing with a key supplier).
About 10 miles from here there used to be one in a drafty warehouse. In winter they put a smelly kerosene heater in the middle ...
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It is good practice to never reveal customers.
I'm not exactly sure I follow the "ringdown" reference. Is this regarding the damping of the transducer?
I'm sure the customer has their reasons, but laser position sensor seems like a better idea to me. I have one in my cruise control. It sets off the laser detector of the car ahead of me. Then again, those ultrasonic sensors in the rear bumpers come in handy. I see newer vehicles are even putting those sensors in the front bumper.
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I gather narrow band implies high Q, hence the ringing.
Not always. For a consultant it would be good if he can mention them, but some don't want to be mentioned and that wish needs to be respected. Another upside of less restrictiveness is when one client has a problem and you can (because another client had allowed it) tell them "This other client of mine may have a nearly perfect solution here" and then the two enter into a business relationship. Win-win in the classical sense.
Yes. That seems to be one of the important parameters in the OP's case.
Hmm, I don't follow that. But I don't know the OP's project as a whole.
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Yes. From the (not very well written) datasheet it seems this is standard PZT-5H or similar material with a backing layer. So the transducer itself is pretty wideband and coupling to a soft media won't change it that much. Then you can fairly easily measure time domain performance with different excitation waveforms. Usually you can't see much of a difference when going from one pulse to a 2-pulse burst, and a very slight pulse response lengthening when going to 3-pulse.
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Your are right about the bandwidth. The information I got from tech support was wrong. It is a wide band device. The scientist wants the frequency to be adjustable to between 200kHz and 500kHz in single cycle pulses that pulse at rate of between 50Hz and 100Hz.
The scientist will need to drive it with a sine wave.
I measured its current today with an oscilloscope using a 1 ohm current sampling resistor. So the oscilloscope would not be exposed to high voltage I measured the ground return current in the coaxial shield. At
500kHz the pulses showed +/-500mV across the resistor. At 200kHz it was +/-200mV. This indicates the load is highly capacitive which is to be expected.The current measurement showed the load is nonlinear. Impedance went lower with increasing voltage.
The Ritec monitor output showed the voltage went up to 1kV. This means at 500kHz I must deliver 500 Watts of peak power. My original plan was to use a DSS chip to generate the pulsing sine wave, buffer its output to higher current, and the step it up with a pulse transformer. But with a typical output of a DSS being 0V to 5V, and assuming the pulse transformer is 80% efficient, and unity gain for the buffer amp, I would need 500A into the pulse transformer. I need a better way to do this.
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Ok, that sounds much closer to standard practice.
Did he say why? This will make the whole setup quite elaborate and expensive. In my 23 years of ultrasound I've never seen a reason to drive a transducer with anything but pulses. Sometimes they get low-pass filtered a bit but not for functional purposes, that's to pass EMC.
It should not be extremely capacitive at its operating frequency range.
I'd seriously discuss the sine wave requirement with the scientist. To me a single-cycle sine doesn't make much sense. If he insist on it you'll have a huge project on your hands.
You can't really generate 500A at the 5V level. Well, you could but it'll be a bear. This is done differently, just like designing and budgeting an RF power amp for radio stations. First you need to find which power transistors are out there at reasonable cost and most of all, available from stock. Look at transistors for 500W-1000W transmitters but sit down before reading the prices :-)
Then look in their datasheets what voltage they like to operate at. This will most likely be in the 20-50V range. Then you'd have to build a multi-stage RF amplifier that can take the miniscule DDS signal and create a stiff RF signal at the 20-50V level. This gets transformer coupled to the transducer so you can run the RF amp at a point where it doesn't get loaded past its design limits. Use (almost) the full available voltage swing at max power since that avoids excessive currents, less heat.
Transformers are nearly free of loss but now for the bombshell: To obtain a reasonably clean sine wave this huge amplifier will have to run with some quiescent current, at least in a mode that RF guys call AB2. This means it'll be generating a lot of heat that you'll have to get rid of via heat sinks and fans.
Another option might be to buy a ham radio transistorized power amp, the biggest honking one there is. But you'll have to heavily modify it because they do not operate below 1-2MHz, meaning new transformers. Also, they usually won't offer gains of more than 20dB so you'd need a smaller amplifier before it.
Not that I want to discourage you but this is going to be a serious project. And it won't result in a small unit.
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The reason for the sine wave is that the system works with what the Ritec RAM-10000 produces and so that is where the confidence is. I was unable test what it would do with a square wave because the Ritec RAM-10000 does not have an option to output this and the lab's function generator was not powerful enough to produce a measurable response in the system.
It is not practical to step up from 5V and 500A with a transformer. So right now I am looking at power op amps from Apex for driving a transformer:
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[...]
No chance to borrow a big pulse generator somewhere? Another option is if another institute near you had a powerful ENI wideband amplifier where you could (almost) get a pulse through that. IMHO it really pays to test a pulse because if a pulse works (and I could bet it will) it'll make your hardware design an order of magnitude easier.
Possibly but it'll be expensive. Also, keep in mind that the GBW product of these is rather low and the slew rate isn't a rocket either.
At its design frequency the transducer usually has a predominantly resistive behavior meaning it'll burn real power, it's not just a capacitor.
If it goes unstable with capacitive loads there is the old trick but it costs even more in slew rate:
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a
=A0... The scientist wants the same
eTrying to do some out of the box thinking here, I recall a scheme that I heard was used by Tektronix. OK, I'll admit I was flipping through their in-house design bible and saw something like what I'm going to describe, and it looked pretty hair brained. What they did was take a good low voltage amplifier, which could be an op amp or discretes, and power it from supplies that form an envelope around the desired signal. So what you are doing is setting up the good amplifier so that it doesn't see much power supply voltage, but rather it moves between rails sufficient to drive the load.
Maybe the envelope supplies could be built from switching circuits (flyback to get the high voltage), then use a linear for the drive. There would be lag in making the envelope votage, but since the sine comes from a DSS, you just use two DSS to produce the sine wave and the needed phase lag for the switcher to catch up.
Essentially similar to patient isolation in medical devices. I had such opamps riding out 5kV defibrillator pulses. Looks like a speck of dirt on a gigantic tsunami. The TUEV guy was mighty impressed that it didn't blow out (he scooted his chair to the other corner of the room before I pressed the big button).
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Around 1980 I was designing an unusual, and very cheap, method to drop voltage from the AC-line.
All the sales staff were all agog.
Someone told them I was about to give it its first test, so they all came into my lab to see.
With everyone crowded around the bench I pressed the button.
Ka-blooie!
Then the line cord burned the length of the bench like a dynamite fuse.
To this day the sales staff think I did it on purpose, just to keep them from lurking in my lab ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine Sometimes I even put it in the food
Hilarious ! I wish I'd been there to see that...
--
Best Regards:
Baron.
Reminds me when you were sure you had designed an indestructible SMPS and then the boss rocked the power switch.
I saw that at an Italian campground, sitting right next to the owner. Phsssouiesssst ... crackle ... kapoof ... tzzzzt ... He poured us all another round of Chianti Classico and said "It'll burn itself out and then I'll fix that tomorrow, or some other time".
So, did ya?
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I once did something like that. I had wired up a line-operated tube amplifier, essentially based on old radio parts. You know, the classics: 35W4 rectifier, 50C5 output, 12AX7 preamp. Perfectly safe with an isolation transformer, but without one, it's also more-or-less safe if, and only if, the neutral is connected correctly.
So it came time to test it. Naturally, I needed a signal source. What better than my computer, right? So I grabbed a Y-splitter, plugged one end into my Sound Blaster 16 (oh, this was back about
1999, on about two-generations-handed-down computer hardware -- think 486!), the other into the amplifier's input, and plugged it in.Pop! Puffs of smoke rose from the splitter cable. Oops, guess that WAS backwards.
The funny thing was, the splitter was evidently so cheap that, not only did it take the place of a fuse, it also burned up at points equally spaced along the cable. So there were little puffs of smoke every couple of inches along the whole thing!
Later testing revealed the sound card survived this nasty surprise. Thank goodness for grounded computer chassis!
Tim
Wasn't the boss, it was my digital equivalent at GenRad Portable Products Division.
No, I neglected to include a hold-off during first application of power, so two TRIAC's fought to the death ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine Sometimes I even put it in the food
I should point out I haven't had a "boss" since '73. Always been by contract. In the GenRad case I had a managerial title and benefits.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine Sometimes I even put it in the food
Title and benefits as a consultant? That's quite unusual.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
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