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TC-08 timing issue?

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TC-08 timing issue?

Postby blackstone » Fri Aug 03, 2012 8:48 am

Hi there,

I have stumbled upon a problem with my TC-08 datalogger. I usually record heating curves of different metals in a 600 °C hot furnace with type-K thermocouples. This week, I tried to differentiate the data to get the heating rates and found that the TC-08 obviously suffers a timing problem when recording data: when I display the calculated heating rates over time in a graph, there are two separated curves shown!

It seems that, at a recording rate of 4Hz (250 ms per measurement), the heating rates calculated from the recorded temperature data with simple difference quotients alternate in pairs, i.e. there are always two values below followed by two values above the what I suppose is the correct, actual heating rate. It seems that temperature values are not recorded every 250 ms, but more like every 200 ms for two times, followed by two measurements with a 300 ms gap. Then the cycle starts again with two 200 ms measurements...

Here's an image to get you an idea how the result looks like:
Image

I am pretty sure that this is faulty behaviour of the TC-08, as I have done this with other data loggers and the results were fine. Could it be that the TC-08 can't actually handle the "high" sample rate? Is there anything one can do about this? Has anybody else experienced this?
Thank's for your help!
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Re: TC-08 timing issue?

Postby ziko » Mon Aug 06, 2012 12:05 pm

Hi,

The USB TC-08 has a single ADC with a conversion time of 100ms, to take the measurements for one channel it also has to read the cold junction, so for one channel the fastest rate you will have is 200ms , for 2 channels it will be 300ms. There may also be some small overhead time.

How many channels are you using?

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Re: TC-08 timing issue?

Postby blackstone » Tue Aug 07, 2012 8:32 am

Hello ziko,

I only used one channel for this measurement. I am wondering how a data aquisition rate of only 4 Hz might be critical for the device, as the TC-08 specs say it should be able to perform 10 measurements per second. Regarding your comment, it seems that the maximum data rate would be only 5 measurements per second, and not 10. :?:

Nevertheless, shouldn't at least 4 measurements per second be feasible (including cold junction and any overhead)?
Is there any way I could have misconfigured the device?

Kind regards!
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Re: TC-08 timing issue?

Postby ziko » Tue Aug 07, 2012 3:11 pm

Hi the 10 measurements in a second is possible if you are using it as a voltage input and not a thermocouple input. In terms of your configuration could you send me you data or settings file?

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Re: TC-08 timing issue?

Postby blackstone » Wed Aug 08, 2012 9:10 am

Could you please specify in detail which file you would like to receive?
I suppose you mean the plw.ini file?
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Re: TC-08 timing issue?

Postby ziko » Wed Aug 08, 2012 9:37 am

Hi the plw data file that or the pls settings file.

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Re: TC-08 timing issue?

Postby blackstone » Thu Aug 09, 2012 3:30 pm

I could not find a .pls file other than the PLAYER.PLS file which seems pretty much useless for me.

A .plw file of a test-measurement contains more info, how should I make it available for you?
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Re: TC-08 timing issue?

Postby ziko » Fri Aug 10, 2012 12:54 pm

Hi to get a pls file you will need to choose File->Save as and then change the "Save as type:" to be settings pls.

In any case send either of the files to support@picotech.com referring to this forum post and myself.

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