topic Re: Basic question TDMS in LabVIEW

Basic question TDMS

Hulk1978 — Thu, 12 Mar 2020 12:18:53 GMT

Hi,

i build a small datalogger. It works now fine.

But i have a strange effect at tdms datalogging. It always stops at around 3h. Sometimes with error 6, sometimes not.

Samplerate is 100 and samples 100,too. So should be 100Hz.

Re: Basic question TDMS

Artem.SPb — Thu, 12 Mar 2020 12:32:25 GMT

What version of OS (32/64?)
File size after stopping?
And what file system?
You may have reached the file size limit in your environment.

upd:

Also show your source code if it is really small. Maybe there is some kind of mistake

Re: Basic question TDMS

Hulk1978 — Thu, 12 Mar 2020 13:07:19 GMT

I´m using windows 10 64bit professionell. Filesystem is NTFS?

Labview is 2016 32bit.

Filesize of tdms is ~15mb after ~3h

Re: Basic question TDMS

GerdW — Thu, 12 Mar 2020 13:21:00 GMT

Hi Hulk,

@Hulk1978 wrote:

But i have a strange effect at tdms datalogging. It always stops at around 3h. Sometimes with error 6, sometimes not.

You are constantly opening the TDMS file, but you are never closing the file!

Open the file once on "start logging" and close it once at "Stop logging", but use the file reference in between!

Btw. is there a reason to have a space at the end of the filename of "create path " VI?

Re: Basic question TDMS

Hulk1978 — Thu, 12 Mar 2020 18:00:31 GMT

Hi Gerd again,

You are seeing all, the space was not wanted.

---

Open the file once on "start logging" and close it once at "Stop logging", but use the file reference in between!

I´m sorry but i didn´t understand

Re: Basic question TDMS

GerdW — Thu, 12 Mar 2020 20:11:06 GMT

Hi Hulk,

@Hulk1978 wrote:

Open the file once on "start logging" and close it once at "Stop logging", but use the file reference in between!

I´m sorry but i didn´t understand

Right now you open a new file ref with each iteration, but NEVER close all those references. Both is bad: no need to open so many references, and each reference you open should be closed too.

Simple solution: open the file once when you start to log data, and close the file once you stop the logging!

Re: Basic question TDMS

BertMcMahan — Thu, 12 Mar 2020 21:50:21 GMT

Note that you could use a shift register in the second loop, but since it's a reference it shouldn't matter for this case.

Re: Basic question TDMS

cbutcher — Fri, 13 Mar 2020 02:53:28 GMT

As a quick further note on references and shift registers:

While loops will always execute at least once. So a tunnel is fine provided you wire it through
For loops can execute zero times (depending on the way their iteration count is controlled - e.g. empty array set to autoindex). This means that the value out of tunnels is the "default default" for the type, which for a reference is invalid. So use a Shift Register with a For loop even with references if the number of iterations can ever be zero (even if you don't expect it to be zero).

Re: Basic question TDMS

Hulk1978 — Thu, 19 Mar 2020 11:36:55 GMT

Hi guys,

i tested the version with permanent open and close the tdms file. That´s not possible. System performance is going down.

The second solution is not possible because i need to open the file inside of while loop. I´m sending the path from the event struct.

Any other solutions?

Re: Basic question TDMS

Artem.SPb — Thu, 19 Mar 2020 11:50:14 GMT

@Hulk1978 wrote:

i tested the version with permanent open and close the tdms file. That´s not possible. System performance is going down.

The second solution is not possible because i need to open the file inside of while loop. I´m sending the path from the event struct.

Any other solutions?

Naturally, it is crazy to open and close the file at every step.
It is very possible to open the file “before” the cycle, for this you need to learn two simple mechanisms: a state machine and a shift register.
Here are three cases in ONE loop. You do not need to do three separate cycles, I showed them only to understand what is happening in hidden cases.

Re: Basic question TDMS

Yamaeda — Thu, 19 Mar 2020 12:21:23 GMT

@GerdW wrote:

Hi Hulk,

You are constantly opening the TDMS file, but you are never closing the file!

Open the file once on "start logging" and close it once at "Stop logging", but use the file reference in between!

Yes, this should be spot on.

With the afforementioned 100 samples/sec and 3 hours you get to 1 million refs, which should stop the system.

Re: Basic question TDMS

cbutcher — Thu, 19 Mar 2020 13:21:41 GMT

@Hulk1978 wrote:

Hi guys,

i tested the version with permanent open and close the tdms file. That´s not possible. System performance is going down.

The second solution is not possible because i need to open the file inside of while loop. I´m sending the path from the event struct.

Any other solutions?

I was going to demonstrate passing the path to the appropriate case, but I see you already do that in your code.

I'd like to suggest that you might find some value in using an enum (as you already are) and a variant as the datatype in order to allow passing more arbitrary "data", but that's up to you and may not be necessary.

As to the path and opening/closing, you should do as Artem.SPb shows and only use TDMS Open in the "Start" case, TDMS Close in the "Stop" case, and then write during the write case.

To handle sometimes logging and sometimes not, you can check if the refnum is a valid refnum using Not a Number/Path/Refnum or you can just always try to write, but ignore the error from an invalid reference (be careful if you choose to do this).

Re: Basic question TDMS

Hulk1978 — Thu, 19 Mar 2020 15:00:34 GMT

hm,

it seems that i need a state machine....

I need more time to reconstruct 😞