CalScope time ?!

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kuengla
Posts: 23
Joined: Thu Jun 26, 2014 12:46 pm

CalScope time ?!

Post by kuengla » Thu Jul 10, 2014 7:21 am

Hi all

In the webapp of the Cal scope the time line can have a big area ( up to 500seconds an more) but my graph stops at 9 second is that normal? how can i see a bigger area on my desktop?

greez kuengla

Kev' Ttn
Posts: 55
Joined: Tue Jun 24, 2014 3:06 pm
Location: Dourdan (France)

Re: CalScope time ?!

Post by Kev' Ttn » Thu Jul 10, 2014 8:12 am

Hi !

I have never used this app, but 500s it seems very huge ! Even 9 second ... How many points does it represent ?

kuengla
Posts: 23
Joined: Thu Jun 26, 2014 12:46 pm

Re: CalScope time ?!

Post by kuengla » Thu Jul 10, 2014 8:23 am

Hi see the attachments ;) at +- 9seconds it stops :( and if i download the data traces it stops at +- 1 second
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Kev' Ttn
Posts: 55
Joined: Tue Jun 24, 2014 3:06 pm
Location: Dourdan (France)

Re: CalScope time ?!

Post by Kev' Ttn » Thu Jul 10, 2014 9:30 am

What is your sampling frequency ? 125MS/s ?

kuengla
Posts: 23
Joined: Thu Jun 26, 2014 12:46 pm

Re: CalScope time ?!

Post by kuengla » Thu Jul 10, 2014 9:31 am

I dont know it must be the default value

Kev' Ttn
Posts: 55
Joined: Tue Jun 24, 2014 3:06 pm
Location: Dourdan (France)

Re: CalScope time ?!

Post by Kev' Ttn » Thu Jul 10, 2014 10:25 am

So it should be 125MS/s.

With this sampling frequency, in 1 sec you acquire 125,000,000 points. Data are acquired on 14 bits ==> 2 octets. The size of the buffer is 250,000,000 octets ==> 238,42Mo.

It is strange, because it means data are transfered into the RAM. I'm maybe wrong but I don't think so ;)

kuengla
Posts: 23
Joined: Thu Jun 26, 2014 12:46 pm

Re: CalScope time ?!

Post by kuengla » Thu Jul 10, 2014 10:45 am

yes i understand it i can't see more becuase 8.58 second is the time i can reach with the maximum decimation =)

Kev' Ttn
Posts: 55
Joined: Tue Jun 24, 2014 3:06 pm
Location: Dourdan (France)

Re: CalScope time ?!

Post by Kev' Ttn » Thu Jul 10, 2014 12:55 pm

So it is normal.

Why ?

Because, the max decimation is 65,356 (cf. acquire.c). So you have a Fs = 125,000,000/65,536 = 1,907.348Hz
And, you have a FPGA memory size of 16,384 points. So it is equal to a time of 16,384/1,907.348 = 8.589s

This is the explication. You have to read all the data which are saved into the FPGA memory before saving news data. Or, the other solution is to use the RAM so save data ^^. But without it, I don't think you can read data in streaming.

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