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DrDaq, External Temperature Sensor, Scaling

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DrDaq, External Temperature Sensor, Scaling

Postby wilba » Wed Nov 30, 2005 6:34 pm

Hi
I am writing a VB6 application with DrDaq to log values to a SQL database.

I am having trouble with getting External Temperature (DD100?) readings.
drdaq_get_value (8) 'Channel 8 - Ext 1

I have confirmed the divider values with drdaq_get_channel_info returns 10. drdaq_get_scalings confirm the selected units are degrees Celsius.

API drdaq_get_value, gives 5.3 PicoLog Recorder gives 6.5
API drdaq_get_value, gives 6.1 PicoLog Recorder gives 7.3
API drdaq_get_value, gives 24.1 PicoLog Recorder gives 24.6
API drdaq_get_value, gives 24.0 PicoLog Recorder gives 24.5

I took the readings a few seconds apart because one cannot run two apps together, so I am not expecting identical readings, but at a lower temperature they seem over a degree out. I have also tried c++ and get the same values.

Is this a non-linear scale? I have run filemon during plw32.exe and cannot find any .dds files that are being used.

I don’t understand why the results are not the same, and how to obtain accurate results?

Thanks
William
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More values

Postby wilba » Sat Dec 03, 2005 11:08 pm

I have collected some more values, that highlight the differences i get when using PicoLog Recorder and the API.

Code: Select all
PicoLog Recorder   API   Difference     What
-9.9   -12.9   3.0   block of ice 1
-8.7   -10.9   2.2   block of ice 2
2.9   1.8   1.1   glass of ice water
8.7   7.7   1.0   outside temp day 3
9.0   8.2   0.8   outside temp day 1
10.7   10.0   0.7   outside temp day 2
16.9   16.2   0.7   beer
21.8   21.3   0.5   inside temp day 3
23.1   22.5   0.6   inside temp day 2
35.6   35.6   0.0   me
37.2   37.0   0.2   girlfriend
48.2   48.0   0.2   hot water from kettle 6
64.3   63.9   0.4   hot water from kettle 5
70.3   70.2   0.1   hot water from kettle 4
77.7   77.5   0.2   hot water from kettle 3
79.9   79.5   0.4   hot water from kettle 2
82.8   81.9   0.9   hot water from kettle 1
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Postby Sarah » Tue Dec 06, 2005 11:28 am

Hi William

Thank you for your posts.

Were you running the programs at the same time? If so then this could account for annomalies - the unit cannot be accessed by two different programs at the same time.

Best Regards
Sarah
 

Postby wilba » Tue Dec 06, 2005 12:16 pm

Hi Sarah

What i did was to start the PicoLog Recorder, wait for the temperature to stabilize.

Then i took a reading, closed it down and started my application and took a reading from that, about 4 seconds.

Sometimes i did it the other way round, but it takes a bit longer.

William
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Postby wilba » Tue Dec 06, 2005 1:32 pm

I have been playing with the Pico Scope.
When i copy values to the clipboard this seems to reflect the differences i have been getting.

William
--------------------------------------------
Pico Scope>Meter>Copy as text
DC Volts 23.1°C
Pico Scope>Scope>Copy as text
Channel
Time Value
(ms) ()
7937 225
7947 226
7957 226....
--------------------------------------------
Pico Scope>Meter>Copy as text
DC Volts 7.6°C
Pico Scope>Scope>Copy as text
Channel
Time Value
(ms) ()
7446 66
7456 65
7476 65.....
--------------------------------------------
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Postby wilba » Wed Dec 14, 2005 2:10 pm

Is there any reason why there are differences?

I would like to move my project along, but cannot because i am not sure i can collect reliable values.

Thanks
William
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Postby Michael » Fri Dec 16, 2005 3:52 pm

Hello William,

The meter window takes more resolve time than the scope window. Therefore you should trust the scope window for more accurate readings.

The scope window also offers additional measurements accessable from the settings/measurements menu.

Best regards,
Michael
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Postby wilba » Mon Jan 16, 2006 11:06 pm

The trouble is there always seems to be some kind of offset for example at the present time the onboard temperature api is returning 246 yet the external temperature sensor that is physically located right next to it is returning 235.

William
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Postby Sarah » Fri Jan 27, 2006 9:06 am

Hi William

You can get rid of an offset by doing an offset null from the settings menu.

Best Regards
Sarah
 


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