Question on use of Piezoelectric sensor:

[H_man]

Hi,

I am aware that in the traditional sense Piezoelectric crystals/ceramics cannot be used to measure static/steady state forces.

However, I was wondering how low their frequency response can go.

That is, is it possible to measure a force of maximum strength 1mN that will develop from zero slowly (over a period of about 0.5-1second) to maximum strength and then dissipate over the same period.

I am worried that my signal will get lost due to the (of course) non-infinite impedance of voltage measuring equipment.

Is my fear justified? Can such a "slowly" varying force be measured?

This is my first foray into the world of such sensitive measurements and any help or suggestions would be appreciated.

Thanks.

 

[enigma]

If I recall correctly, you can go down to around 10Hz with PZT. Anything slower than that you'll have to worry about bleedoff.

Is there any reason a simple strain gage would not work for your application?

 

[H_man]

Thanks Enigma,

Yup, I can´t use a strain gauge as I am measuring the impulse from a plasma plume. The high temperatures would kill the gauge very quickly.

I stopped thinking about PZTs some weeks ago as I didn´t think they would work due to the long build-up time of the pulses(even though there are devices I found than can withstand temp. of up to 1100K).

I have other ideas but my supervisor (who is a theoretician) was quite insistent that I use a PZT and I was quite insistent that it wouldn´t work.

There will have to be another tense meeting...

 

[Danger]

Is there perhaps some way that it can be done optically or accoustically? I don't know anything about it; just throwing out a thought. Something perhaps like having a standing air mass of known properties in the plume path, with a funnel or tube leading to a transducer to measure the pressure increase.

 

[H_man]

Thanks for the suggestion Danger, but unforunately that's not possible as the plume is being generated in a vacuum (you also have to consider the incredibly high temp. of the plasma).

I think I have found the solution in some electronics to control the period of the plasma pulses (and so use the PZT s but just at a much higher freq.).

But originally I just wanted to make sure that I wasn't wrong about the PZTs poor response at low frequencies... as I have another meeting tomorrow.

 

[Danger]

Yeah, I guess that introducing an air mass would to some small degree compromise the integrity of your vacuum.
I didn't know that the pulse frequency could be adjusted. It seems that you've found a good solution. Good luck at the meeting. Keep us posted.

 

[enigma]

Thanks Enigma,

Yup, I can´t use a strain gauge as I am measuring the impulse from a plasma plume. The high temperatures would kill the gauge very quickly.

I stopped thinking about PZTs some weeks ago as I didn´t think they would work due to the long build-up time of the pulses(even though there are devices I found than can withstand temp. of up to 1100K).

IIRC, the high temperatures will depole the crystals pretty quickly. I'm actually kind of surprised that they're advertising 1100K.

Are there any magnetic properties of the plume you could utilize?

Could you draw a quick sketch of the proposed experimental setup?

 

[H_man]

The K-12 material in the table on their website is listed for applications up to around 1000K.

http://www.piezotechnologies.com/materialssheet.htm

I was pretty surprised myself

I have the data sheet for the material which does show how properties vary with temp. Although, unforunately it doesn't show the effect of repeated heating and cooling cycles.

My gut feeling is that if I am to use the PZT its going to have to be contained within some kind of cooling jacket, perhaps with water (in a sealed pipe) helping draw the heat away. Also... I won't be letting the plasma directly impinge on the crystal.

As for how the setup is going to look... I am fairly free to orientate things as I wish. As for hows its going to look , your guess is as good as mine.

As for magnetic properties of the plume... this wouldn't help an impulse measurement.

I'll keep you informed...

 

[nivalis]

hi,
can I use peizoelectric sensors to obtain and record the low substrat vibrations? if ı use, how can ı do?
thanks in advance

 

[rollydanver]

I'v ever one time saw one introducing article on the peizo sensors application from one web . It has a quite detailed data sheet on it ...Hv to recall the memory ...seems frequency decided the sense like that .

 

[rollydanver]

hi,
can I use peizoelectric sensors to obtain and record the low substrat vibrations? if ı use, how can ı do?
thanks in advance

YES . OFX U CAN . It is up the sensors u chose.