Piezoelectric and normal force sensor
Piezoelectric and normal force sensor
(OP)
Hi,
I would like to know if someone has references or ideas about the use of a piezoelectric force sensor in parallel or in series with a normal force sensor.
The piezoelectric force sensor can sense dynamic forces but loses its charge. On the other hand the normal force sensor can't measure small forces but keeps the static force.
My idea would be to sense very small dynamic forces while holding a large static force.
Do you think it would be possible and does someones has references on this ?
Thank you very much !
Alex
I would like to know if someone has references or ideas about the use of a piezoelectric force sensor in parallel or in series with a normal force sensor.
The piezoelectric force sensor can sense dynamic forces but loses its charge. On the other hand the normal force sensor can't measure small forces but keeps the static force.
My idea would be to sense very small dynamic forces while holding a large static force.
Do you think it would be possible and does someones has references on this ?
Thank you very much !
Alex





RE: Piezoelectric and normal force sensor
RE: Piezoelectric and normal force sensor
What I was thinking is by having a model of the lost of charge in the piezo and combining with the normal force sensor, I guess I could know the actual small forces.
I am then trying to see if it is possible and if there is literature on this.
Thank you very much!
Alex
RE: Piezoelectric and normal force sensor
I'd talk to the people at Kistler (piezoelectric) and Interface (strain gage) and see what they say.
With a good strain gage load cell, conditioner and cabling, I've seen noise levels on the scope less than 10 mVpp for a full scale output of 10 Vpp. So with a good strain gage setup you should be able to cover nearly a 1000:1 range.
RE: Piezoelectric and normal force sensor
RE: Piezoelectric and normal force sensor
I haven't seen any posts on that subject before...I am new but I searched the database without any results...
The static load does not vary...it is static. The signal from a normal strain gage would be be noisy in comparison of the dynamic force because for a 1500N strain gage sensor there would be a lot of noise (in the range of the dynamic force). (For example the 1500N force is a mass and while moving there is vibrations). It is then hard to see if a 1N dynamic force is real or vibrations or sensor noise.
I will look for Kistler and Interface and give news !
Thank you all !
Alex
RE: Piezoelectric and normal force sensor
Alex
RE: Piezoelectric and normal force sensor
anyways, please clarify "in general it is very noisy". if the static force is very static (ie stable) what's the noise ? does the dynamic force a very short wavelength/period ? does the sensing sytem need to respond very quickly, and measure a small signal very accurately ??
i know you can modify a wheatstone bridge to increase the sensivity of the strain gauge, get a bigger ouput for a samll signal. however i suspect that doing this increases the reaction time of the system, decreases the ability of the mesuring system to detect short wavelength signals.
RE: Piezoelectric and normal force sensor
The noise does not come from the static force. Normally a strain gage sensor with a 2000N range will by itself have a lot of noise. It is why it is hard to obtain a small force. A lot of filtering implies bigger reaction time.
The dynamic force can vary, it can change very fast (10ms response maybe or more, not sure) but also be static during a minute. The sensing system would have to respond in the order of 10 ms. The small signal accuracy is not that important, 1.2 N instead of 1N is not dramatic...
I will look for the Wheatstone bridge, that looks promising. Do you think the effect of a low-pass filter would be the same ??
For the previous thread, maybe someone with who I work posted it...Do you know why it was deleted ?
Thank you very much !
Alex
RE: Piezoelectric and normal force sensor
so the dynamic signal can be very brief, or quite long in duration.
are you trying to detect the dynamic load, by measuring it's effect on some structure ? that looks to me doomed, depending on the structure's response rate.
talk to the strain guage folks ...
RE: Piezoelectric and normal force sensor
There is noise in a sensor. Even with no forces on it, there is noise for a hundred reasons, mainly in the cables going to the computer, small vibrations, etc...For large scale sensors, this noise is more important. No I am not trying to measure the dynamic load with it's effect on the structure. It could be though. Because the force I want to measure can be measured with a normal low range force sensor. The problem come from the static force and all the problems coming with it.
RE: Piezoelectric and normal force sensor
Do you really mean to group "small vibrations" and noise together? I think your concern is electrically induced noise in the wires, right?
RE: Piezoelectric and normal force sensor
A -200 to 200N range sensor provide a signal between -5V and 5V. With a noise of for example 0.01V after filtering, that makes a 0.4N noise.
A -2000 to 2000N range sensor provide the same signal -5V to 5V signal with the same 0.01V noise. But now it translates in a 4N noise, after decent filtering. This is why we can't get the small 1N force out of a big sensor.
I think that's the explanation. Now the idea was to use a piezo and a strain gage together and to mix their properties. I will look with the companies and if you have more informations, thank you to share !
Thank you all !
Alex
RE: Piezoelectric and normal force sensor
RE: Piezoelectric and normal force sensor
RE: Piezoelectric and normal force sensor
until very close to balance and then a very sensitive force detector gets the final weight. An additional benefit of counterweights is that vibrational noise can also be canceled out to some extent.
RE: Piezoelectric and normal force sensor
I have been thinking of balancing the weight but the problem is that with a counterweight it would be very very cumbersome and I would have to move this extra weight! Also, the static force can change (I would know this change and I don't want to measure the force while this change).
I also have been thinking about balancing with spring but there is too much vibrations with these.
Thank you !
Alex
RE: Piezoelectric and normal force sensor
Out of curiosity I just looked at Detecto's web site and some of their digital scales. They claim to have a 2000:1 ratio (20 lbs FS, .01 lbs resolution) on some of their scales.
You might want to ask the electrical guys (Circuit Design Forum) here what they think is possible.
Let us know what the Kistler and Interface guys (or whomever) say about your application.
RE: Piezoelectric and normal force sensor
Yes I will use shielded cables but there will still be noise. What I meant is that extra shielded cables would be expensive. I may have 3 meters cables so there is a lot of noise accumulations. I looked at Detecto but they do balances where they have a lot of spaces in the balances for signal conditioning but more importantly they do not have long cables...the display is at the balance. There is nothing to do with the noise except normal filtering. It is why I was looking at other solutions as a piezo and strain combine or balancing solutions as Compositepro solutions.
Still no answer from the companies, I'll let you know.
Thank you all for your answers !
Alex