[RASMB] Re: XL-A/I temp control

mchien at beckman.com mchien at beckman.com
Fri Dec 3 13:13:01 PST 2004


Hi All,

Below is response regarding XL-A/I temperature control from our Technical
Support Department.

******************************************************
Mei-Ling Chien PhD
Staff Development Scientist, Centrifugation
Platform & Automation Business Center
Beckman Coulter Inc.

mchien at beckman.com
(650) 859-1948
******************************************************


The basis for temperature control specifications were instrument design
specifications for temperature control and dynamic system testing during the
prototype phase of the product.

If there is a discrepancy in temperature control and measurement between
instruments of the same design then a dynamic calibration check should be
performed on both instruments to ensure their operation within the published
specification.

First the physical condition of components within the temperature control and
vacuum system should be verified through inspection.  Then an electronic
calibration for temperature control and vacuum can be performed.  Lastly a
dynamic test or rotor dunk test is performed (rotor should be precooled or
preheated to avoid testing delay).  The rotor and its contents must be allowed
to equilibrate for up to 3 hours or more.  When set temperature equals indicated
temperature at the instrument interface, the rotor temperature is then checked
with a calibrated external temperature sensing device to verify accuracy.

If the checks fall out of specification then appropriate troubleshooting is
required to isolate the electronic or mechanical fault in the temperature
control or vacuum system.  Once the fault is corrected the temperature control
checks are performed again.

Quote from Bob Giebeler, Analytical Ultracentrifugation in Biochemistry
     and Polymer Science, 1992,16-25 for the Optima XLA/I.
"Temperature  control is considerably more stable, provides more rapid cool-down
and  heat-up  rates,  is  thermally more uniform, and has equivalent accuracy as
compared  to previous models including the Model E.  This control system uses an
isothermal radiometer temperature-sensing system to sense the temperature of the
rotor  that  is  emissivity-independent  ad  view  factor-corrected in software.
Heating  and cooling of the rotor are accomplished by the refrigeration can that
surrounds  the  rotor,  which  is  in  turn  heated and cooled by thermoelectric
modules.   This environment is very isothermal, and at equilibrium, irrespective
of  speed  or  temperature,  rotor temperature is within about one degree of the
refrigeration can temperature.


The  control  system  that  regulates  rotor  temperature,  as  monitored by the
radiometer,  is  highly  software-intensive.   This  software encompasses triple
proportional-integral-differential  control algorithms and proportional-integral
smoothing  algorithms.  In addition, radiometer view factors are measured during
rotor   cool-down  to  allow  more  rapid  rotor  cool-down  and  more  accurate
temperature  monitoring  during  cool-down.  While at equilibrium, refrigeration
can   temperature   fluctuation   does  not  typically  exceed  +0.5C,  and  the
corresponding rotor temperature fluctuation is less than +0.2C.














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