volume flow per second - from pulse flowmeter

 Hello Jacek

I don't understand how I can take value from previous cycle/interrupt ?

In OB interrupt I have only  value read once per second and this is so cold "new value".

jacek d

New value - current value of the counter.

Old value - value of the counter from previous cycle/interrupt.

Once the calculations in current cycle are done, the new value must be written to the old value.

 qwazee i don't undestand what you mean completely...

qwazee

To assist Mr. Einstein, please show also what the filter time is on the input.

Leszek Jaszczak

 qwazee i don't undestand what you mean completely...

qwazee

To assist Mr. Einstein, please show also what the filter time is on the input.

 For each input used by HSC ->

Leszek Jaszczak

Hello Jacek

I don't understand how I can take value from previous cycle/interrupt ?

In OB interrupt I have only  value read once per second and this is so cold "new value".

jacek d

New value- current value of the counter.

Old value- value of the counter from previous cycle/interrupt.

Once the calculations in current cycle are done, thenew valuemust be written to theold value.

Sorry mate I've just collapsed. 

I'll elaborate on this then. You have the current reading of the counter. So in the code, once you are done with calculations, you save it to a variable  - say, called previousValue. E.g.: 

currentFlow := currentCounterValue - previousValue;//calculations here

previousValue := currentCounterValue;//copying here

Of course  previousValue should be declared in a DB or alike for the code to work. This way in each OB call you have actual counter value and previous one.

A question can arise, what with the very first run of the OB. Here are two strategies - set it to 0 or to current value.

qwazee thank you for advise 

it is 6.4 ms - attachement

Leszek Jaszczak

Jacek sorry but your calcuclation gives me "0" or value goes from 0 to 10...math dosen't work or I am still doing something wrong, please take a look at video.

I disagree. My calculations work. 

With the other statement I agree - you are still doing something wrong.

This something is subtracting in one block and copying in the other. If I got your code right, you should move SUB block from the window on the right side and place it just before MOVE in the window on the left side.

Dear Jacek   finally I have found mistake, thank you for help. The mistake was that I was placing MOVE before substraction.

When it was before I get calculation result "0" - see attachemnt end of video.

When I moved it as you wrote - SUBSTRACT before MOVE then it start to work. This was the most important words for me. Thank you. 

Now as I understand OB interrupt block read ones per second "new value", instruction MOVE change after one second "new value" to "old value", next substraction is beeing done also after one second and this gives result = 10 hz

I am still not sure why it works that way, I know that program works from top to down.

The best way of learnig for me is working with the problem.

Anyway thank you for help and patience Jacek  

It is great to have this forum and pepole like you Einstein and Jacek 

jacek d

 

Leszek Jaszczak

Jacek sorry but your calcuclation gives me "0" or value goes from 0 to 10...math dosen't work or I am still doing something wrong, please take a look at video.

I disagree. My calculations work. 

With the other statement I agree - you are still doing something wrong.

This something is subtracting in one block and copying in the other. If I got your code right, you should move SUB block from the window on the right side and place it just before MOVE in the window on the left side.

Leszek Jaszczak

qwazee thank you for advise 

it is 6.4 ms - attachement

Sorry for a late response.

The filter setting has the ability to kill a fast pulse. The default is 6.4ms is a very bad setting for most applications that need HSC functions.

The lazy way is to reduce the filter to the smallest value that is offered as a filter. The more proper way is to calculate the filter time that you require.

As a rule-of-thumb, I use a factor of 10. Assume f_max is the fastest possible pulse that the input should detect. Assume t_filter is the input filter time. t_filter = 0.0064s is the default.

              1
t_filter = -------------   seconds
          (10 x f_max)

 
Sanity and good health!