<HTML>
<HEAD>
<TITLE>Re: [RASMB] Re: XL-A/I temp control</TITLE>
</HEAD>
<BODY>
Hi Everyone <FONT COLOR="#000080">{this is a second (</FONT><FONT COLOR="#FF00FF">now 3rd!</FONT><FONT COLOR="#000080">) try at getting this mail out - first attempt got lost in cyber-space, it seems}<BR>
</FONT><BR>
Mei-Ling Chien gives us a very useful review of the nature of the temperature measurement and control system in the XL-I/A instrument. However, I do not think that this fully addresses the problems which one has in determining what the absolute temperature of one's sample actually <I>is</I> when it is going round in the rotor at speed.<BR>
<BR>
It is, of course, only a worry to those (very limited) number of people for whom an absolute s value is of importance, normally for hydrodynamic modelling purposes (although formulation issues should not be forgotten). When I raised this issue on RASMB a week or so back, my concern was not "<FONT COLOR="#FF0000"><TT>to ensure their operation within the published specification".</TT></FONT> . I am trying to get the <U>accuracy</U> of the temperature read-out to be close to the <U>precision</U> of which the system is capable. I have no evidence at all to suggest that the accuracy is outside the quoted spec of 0.5º. It is just that I - in my greedy way - want 0.1º.<BR>
<BR>
Even the method mentioned (equilibrate for 3 hours - under vacuum - and then check "<FONT COLOR="#FF0000"><TT>with a calibrated external temperature sensing device to verify accuracy"</TT></FONT> is not unambiguous in what it will yield. Quite apart from matters such as adiabatic effects when one releases the vacuum to use an "external temperature sensing device", can one be sure that the thermal emissivity of a spinning rotor surface, averaged over everything that is passing by, is equal to that of a piece of the rotor surface 'seen' in a stationary rotor? <BR>
<BR>
None of these are new concerns, and I certainly lay no claim to the IPRs! I imagine, from what Mei-Ling Chien has communicated, that we at least know clearly that the ±0.5º refers to the accuracy of the temperature <U>as measured by the defined procedure</U>. Walter Stafford's colorimetric method (Stafford & Liu) did not suggest the presence of errors outside the stated accuracy limit, and is surely a valid way to approach the absolute temperature issue. But is is pretty tedious to use as a procedure, and certainly as a routine QA method is not feasible. <BR>
<BR>
<FONT COLOR="#008000"><I>As an approach to the size of the problem, would there be support for Borries Demeler's suggestion (a single sample to be circulated and multiple users on multiple machines to report an s value under defined conditions)? After all, the NCMH + Borries's Lab gives us 6 machines for starters.<BR>
</I></FONT><BR>
Any way, we here keep trying here to locate the holy grail - a simple, cheap, effective method for determining the in-cell temperature to ±0.1º <BR>
<BR>
Regards to all (and many thanks to Mei-Ling Chien)<BR>
<BR>
Arthur<BR>
<BR>
-- <BR>
*************************<BR>
Arthur Rowe<BR>
Lab at Sutton Bonington<BR>
tel: +44 115 951 6156<BR>
fax: +44 115 951 6157<BR>
*************************<BR>
<BLOCKQUOTE><BR>
<B>From: </B>mchien@beckman.com<BR>
<B>Date: </B>Fri, 3 Dec 2004 10:11:46 -0800<BR>
<B>To: </B>"'rasmb@rasmb-email.bbri.org'" <rasmb@server1.bbri.org><BR>
<B>Subject: </B>[RASMB] Re: XL-A/I temp control<BR>
<BR>
</BLOCKQUOTE><BR>
<BLOCKQUOTE><TT>----------------------------------------------------------------------------------<BR>
The older archived RASMB emails can be found at:<BR>
http://rasmb-email.bbri.org/rasmb_archives<BR>
and current archives at<BR>
http://rasmb-email.bbri.org/pipermail/rasmb/<BR>
Search All the Archives at:<BR>
http://rasmb-email.bbri.org/rasmb_search.html<BR>
----------------------------------------------------------------------------------<BR>
<BR>
Hi All,<BR>
<BR>
Below is response regarding XL-A/I temperature control from our Technical<BR>
Support Department.<BR>
<BR>
******************************************************<BR>
Mei-Ling Chien PhD<BR>
Staff Development Scientist, Centrifugation<BR>
Platform & Automation Business Center<BR>
Beckman Coulter Inc.<BR>
<BR>
mchien@beckman.com<BR>
(650) 859-1948<BR>
******************************************************<BR>
<BR>
<BR>
The basis for temperature control specifications were instrument design<BR>
specifications for temperature control and dynamic system testing during the<BR>
prototype phase of the product.<BR>
<BR>
If there is a discrepancy in temperature control and measurement between<BR>
instruments of the same design then a dynamic calibration check should be<BR>
performed on both instruments <FONT COLOR="#FF0000">to ensure their operation within the published<BR>
specification.<BR>
</FONT><BR>
First the physical condition of components within the temperature control and<BR>
vacuum system should be verified through inspection. Then an electronic<BR>
calibration for temperature control and vacuum can be performed. Lastly a<BR>
dynamic test or rotor dunk test is performed (rotor should be precooled or<BR>
preheated to avoid testing delay). The rotor and its contents must be allowed<BR>
to equilibrate for up to 3 hours or more. When set temperature equals indicated<BR>
temperature at the instrument interface, the rotor temperature is then checked<BR>
<FONT COLOR="#FF0000">with a calibrated external temperature sensing device to verify accuracy</FONT>.<BR>
<BR>
If the checks fall out of specification then appropriate troubleshooting is<BR>
required to isolate the electronic or mechanical fault in the temperature<BR>
control or vacuum system. Once the fault is corrected the temperature control<BR>
checks are performed again.<BR>
<BR>
Quote from Bob Giebeler, Analytical Ultracentrifugation in Biochemistry<BR>
and Polymer Science, 1992,16-25 for the Optima XLA/I.<BR>
"Temperature control is considerably more stable, provides more rapid cool-down<BR>
and heat-up rates, is thermally more uniform, and has equivalent accuracy as<BR>
compared to previous models including the Model E. This control system uses an<BR>
isothermal radiometer temperature-sensing system to sense the temperature of the<BR>
rotor that is emissivity-independent ad view factor-corrected in software.<BR>
Heating and cooling of the rotor are accomplished by the refrigeration can that<BR>
surrounds the rotor, which is in turn heated and cooled by thermoelectric<BR>
modules. This environment is very isothermal, and at equilibrium, irrespective<BR>
of speed or temperature, rotor temperature is within about one degree of the<BR>
refrigeration can temperature.<BR>
<BR>
<BR>
The control system that regulates rotor temperature, as monitored by the<BR>
radiometer, is highly software-intensive. This software encompasses triple<BR>
proportional-integral-differential control algorithms and proportional-integral<BR>
smoothing algorithms. In addition, radiometer view factors are measured during<BR>
rotor cool-down to allow more rapid rotor cool-down and more accurate<BR>
temperature monitoring during cool-down. While at equilibrium, refrigeration<BR>
can temperature fluctuation does not typically exceed +0.5C, and the<BR>
corresponding rotor temperature fluctuation is less than +0.2C.<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
_______________________________________________<BR>
RASMB mailing list<BR>
RASMB@rasmb-email.bbri.org<BR>
http://rasmb-email.bbri.org/mailman/listinfo/rasmb<BR>
</TT></BLOCKQUOTE><TT><BR>
</TT>
</BODY>
<br/>
<p>
This message has been scanned but we cannot guarantee that it and any
attachments are free from viruses or other damaging content: you are
advised to perform your own checks. Email communications with the
University of Nottingham may be monitored as permitted by UK legislation.
</p>
</HTML>