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<TITLE>Re: [RASMB] Re: An early Christmas puzzle</TITLE>
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<BLOCKQUOTE><FONT COLOR="#800000">Hi John<BR>
<BR>
Many thanks for your interesting thoughts. You should certainly know more than most of us on the topic of temperature control.<BR>
<BR>
I am sure you are correct to emphasise the distinction between the level of control attainable and the absolute accuracy of what is measured by your detector. As the detector in the instruments <I>does</I> pick up signal - when the vacuum is down - more or less in the relevant place (rotor, more or less where the cell is), and as that signal is steady to around ±0.1º, maybe we can have a bit of confidence that whatever is being controlled <I>is </I>controlled pretty steadily and reproducibly (see my mail to Marc Lewis). What we do not know is just what systematic error is involved. <BR>
<BR>
Anyone from Beckman want to comment on this? What is the basis for that ±0.5 degree figure, for example?<BR>
<BR>
Kind regards<BR>
<BR>
Arthur<BR>
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<TT><BR>
<BR>
Arthur Rowe <arthur.rowe@nottingham.ac.uk> was asking a question about<BR>
temperature control in his apparatus.<BR>
<BR>
I can't pretend to know about AUC- I joined the list as a lurker to try to<BR>
understand a bit about what some of our customers do with our software.<BR>
However, I did spend about 25 years in a lab, some of that time spent<BR>
using temperature controllers.<BR>
<BR>
1. The temperature controller's spec (unless there is something to say<BR>
otherwise) tells you how closely the controller will control the measured<BR>
temperature. It does not include things like calibration error in your<BR>
thermocouple (or RTD or thermistor, or whatever).<BR>
<BR>
2. In my experience, the largest source of error in temperature control is<BR>
not in the controller, but in temperature gradients. The temperature may be<BR>
known to within 0.5 degree where it is being measured, but what is the<BR>
temperature at the ends of the sample? (Hopefully the sensor is placed near<BR>
the middle of the sample chamber)<BR>
<BR>
>Given the type of error distribution expected, can we really accept that<BR>
>it is better, using 2 instruments, to get 2 estimates for an s value that<BR>
>dis-agree than 2 which agree? Or is this believing in Santa Claus?<BR>
<BR>
I think it's Santa Claus. As I said, you know that the controller is<BR>
keeping the measured temperature within a half degree, but you don't know<BR>
much about other sources of error.<BR>
<BR>
I will now remove myself from an argument where I don't really have<BR>
expertise :)<BR>
<BR>
Regards,<BR>
John Weeks<BR>
<BR>
WaveMetrics, Inc.<BR>
Phone (503) 620-3001<BR>
Fax (503) 620-6754<BR>
email support@WaveMetrics.com<BR>
<BR>
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