How to reject pulses

Question

Hi,
This is one project that I am doing for some time using sinar sensor which generates pulse with to measure the distance to object. This sensor is being controlle dby basic stamp2.
My problem is that I am getting signal from the signal out put of the sensor. the same output is used by the basic stamp to switch on the sensor and that time is like 2usec so it acts like pulse the sensor generate long pulse depending upon the distance from the object. SO one short pulse and one long pulse
but I dont want my labview to read this short pulse which is like constant 2Usec,
because I am trying to calculate the velocity out of that range sensor so I onle need pulses which tells me the distance so two consecutive distance pulses in my code will tell me change in distance and the I can convert it into velocity.
But if small pulse I call it triggering pulse is read by the code then it will not be two consecutive distance but will be alternate small large small large
Now I have tried to used the case structure telling it that if time measures is greaterthan this than it is true and process but what happens now is that when it recieves small pulse the case structure repeats the variable like repeat the distance again
see my attachment
How to get rid of this small pulse that it does not go into my while loop
Attachments:
combine1b.vi ‏158 KB

Answer 1

The cause of the problem is that you were using the case structure to control the data update of the local variable, but you were not using it to control whether the data is processed for a given iteration of the loop. What this meant is that you would process old data during iterations in which you didn't want to process any data. The simple fix is to include all of your processing inside of your case structure. This also allows you to eliminate the use of local variables, which should always be avoided at all costs. The use of that local variable actually created a race condition in your code which could have also contributed to the problem you were having.
I have attached a modified version of your code that implements what I described above. I hope this helps and remember the lesson to learn: use local variables as a last result only!
Kind Regards,
E. Sulzer
Applications Engineer
National Instruments
Attachments:
combine1b_mod.vi ‏160 KB