ACCELERATION

HI.

PLEASE I WANT TO CALCULATE THE ACCELERATION FROM SPEED DATA  WITH SCL LANGUAGE ON STEP7 . HOW CAN I DO IT ? PLEASE HELP 

Some basics: 

https://en.wikipedia.org/wiki/Acceleration

https://en.wikipedia.org/wiki/Numerical_differentiation

Hi jack, 

I have already developed a script ( attached file) to get speed information into a analog input. but I want to calculate the acceleration of a wheel based on acceleration relation. thanks for your help!

My solution would be this:

since we know that acceleration is the derivative of speed, then we need to calculate it two things :

1) (Interval of) time

2) (Interval of) speed

To do good things I think you can use a TIMED OB , with a fast scan time cycle, and everytime you launch that OB you get the speed and you make the difference of that speed - the old one, read at the previous cycle.

FC_Acceleration_Calculator

rDeltaSpeed = rActualSpeed - rOldSpeed;

rActualAcceleration = rDeltaSpeed / rScanTime;

rOldSpeed := rActualSpeed;

<END OF FC>

rScanTime (I think it's an integer, but what ever.... Is the scan time of the OB you used to launch this simple FC, you can set it in the configurations of the OB and I suggest you 5 ms for example or 10 ms, just to not exagerate with resource drain. Unless this calculation is critical, then the less is the scan cycle, the better is the measure

Regards,

Davinator

hi. 

But I want to do this calculation in my script  without use OB ! 

mohamedarrach

hi. 

But I want to do this calculation in my script  without use OB ! 

The more accurate the time measurement is, the more accurate the calculation. From the code it seems you already have all you require. You have a table of measured speed at regular intervals - right?

Please mention - Which software (Step 7 V5.?) and PLC are you using?

BR

mohamedarrach

hi. 

But I want to do this calculation in my script  without use OB ! 

 What you mean for script ?

When I program S7 family I use OB,FB,FC,DB but not script... It's not a PC with visual basic ;)

Or maybe you want do this all by using a TP panel so you need VB script ?

Im using step7 version of  5.5.  I dont have a specific table to calculate the acceleration, I jut want to calculate it in real time with a period of 100ms for examlpe and apply a condition on it. example of the condition that I want: 

function acc:void

var_temp 

a:array[1..6] of real; \\acceleration

v:array[1..6] of real; \\speed

begin 

for i:=1 to 6 by 1 do

a[i]:= v_actual-v_old /period; 

if a[i]> 20 then circuit_breaker :=true end if; 

end_for;

end_function

Hi. Im still waiting for your help ! How can I get the acceleration from speed with relation a=dv/dt in scl language. 

Hello.

mohamedarrach

Hi. Im still waiting for your help ! How can I get the acceleration from speed with relation a=dv/dt in scl language.

It would benefit you to read the articles that long standing expert jacek d supplied. It is not clear as to what you aim to do with the acceleration or how the speed change profile looks like. Knowing this information will help in determining if an extensive algorithm is needed or a simplified one.

When the time difference is very small the moment differentiation is as I have shown in the picture. This is a simplified version. The 100ms period is not small. This will be not be a problem if change in the speed is linear.

BR