Acqusitioning signal from sonar sensor and filtering

Question

Hi
I am using sonar sensor to caclulate the distance and velocity of my robot vehicle. If I look at signal in Ocope for distance measurement I have two signal(see attachment) one shorter pulse width which is command from host controller to sonar sensor to emit burst this shorter pulse is like 2 micro second and then when the echo returns I have larger pulse this pulse width depends upon the ditabce from the object--larger pulse width is from 115 microsecond to 18.5 millisec. Since I want to calculate the velocity of my robot I need only larger pulse width and if I take difference of two consecutive larger pulses it will give me the velocity.
but in present case I get pulse width of two consecutive as one larger and one smaller every time. My question is how can I filter or reject shorter pulse from my calculation.
see my attachments for Oscope which is exactly what the signal should look like. But the signal which I am capturing in Vi is all edgy how can I take good signal in Vi and how can I get pulse width for only echo that I receive in sonar and not shorter pulse in order to calculate further my velocity and stuff.
thanks
Attachments:
labcapture.zip ‏432 KB

Answer 1

Hi
I captured the signal in Vi that came with NI examples cont acq & graph voltage-int clk.vi . I mentioned earlier since sonar sensor emits small ping and then larger pulse tells you about the distance larger the pulse farther the distance ideally speaking I must see one small pulse and one larger pulse but I can see the larger pulse but instead of small I am looking at some noise or distortion. so pattern I am getting is large pulse and then distortion , larger pulse then distortion and so on. If I am able to remove that noise the larger pulse width is my distance which I want further for my calculation. Look at the attachments.
What do you suggest?
My Vi was same as I posted only I have attached graphic indicator more in the Vi.
Due to this recurrent distortion I get some wrong constant data and number alternatively which makest my delta X i.e dstance same
for example distortion every times give me 0.17 distance so if disance is like 20 cm my display will work like 20--0.17---21---0.17--22---0.17 so if I take deltax that is difference between twoconsecutive distance change which should be like difference between 22-21=1 it actually becomes 22-0.17=20.93 and next time it calculates 0.17-23=-22.83 which becomes wrong.
If I remove this distortion or tell my Vi not to read below certain votages--- how can I do that.
Since you mentioned increase the thresh hold how we do that and how to remove this distortion just see my captures of the signal.
Thanks
Attachments:
signal1.zip ‏110 KB