TEMPERATURE CONTROL OF NEAR-INFRARED ANALYZER

REGULATEUR THERMIQUE D'UN ANALYSEUR INFRAROUGE PROCHE

English Abstract

A preferred temperature control
strategy was devised to remove heat from the
analyzer and control the optical bench
temperature continuously at aim. A foil-type
RTD temperature detector is fastened to the
optical bench to serve as a measurement
input device for a PID control strategy, which
is truly aim-seeking. The control strategy
employs a heat pipe technology to remove
heat from the analyzer enclosure. A heat
pipe utilizes a fluid (such as an alcohol) to
remove heat by evaporation of the fluid at
an internal air circulation heat exchanger
and then recondensing the fluid at an
external air circulation heat exchanger. The
PID temperature controller achieves the
desired temperature setpoint by manipulation
of heat exchanger fan speeds. The heat
removal rate can be very precisely
controlled. In practice, both heat exchanger
fans could be controlled together, however,
to achieve optimal internal temperature
uniformity, the internal heat exchanger fan is
maintained at full speed and just the
external fan is controlled to adjust heat removal
rate. Optical bench temperature control is
maintained to plus or minus 0.1 degree C
vs. a typical temperature control band of
plus or minus 2 degrees C.

French Abstract

Le procédé préféré de régulation de température de la présente invention a été conçu pour éliminer la chaleur de l'analyseur et réguler à un niveau nominal continu la température d'un banc optique. Un détecteur de température à résistance du type "à feuille" est fixé sur le banc optique où il fait office d'organe de saisie de la mesure pour un procédé de régulation par action PID, approchant le nominal vrai. Le procédé de régulation met en oeuvre une technique de tube à chaleur pour éliminer la chaleur de l'enceinte d'analyseur. Ce tube à chaleur utilise un fluide (tel qu'un alcool) pour éliminer la chaleur par évaporation du fluide dans un échangeur de chaleur à circulation interne d'air. Le régulateur de température par action PID permet d'atteindre le point de consigne de température souhaitée en intervenant sur les vitesses des ventilateurs d'échangeurs de chaleur. Le taux d'élimination de la chaleur peut ainsi être très exactement régulé. Dans la pratique, il serait possible de commander ensemble les deux ventilateurs d'échangeurs de chaleur. Toutefois, pour une uniformité optimale de la température interne, le ventilateur de l'échangeur de chaleur interne est maintenu à plein régime, alors que le ventilateur de l'échangeur de chaleur externe est seul soumis à la régulation produisant le taux exact d'élimination de la chaleur. Grâce à ce procédé, il est possible de réguler la température du banc optique avec une marge de plus ou moins 0,1 DEG C, alors que cette marge était de plus ou moins 2 DEG C avec les procédés traditionnels de régulation de température.

Claims

5



What is claimed is:

1. An apparatus for continuously controlling to within plus or minus
0.1°C the temperature
of an analyzer cabinet having critical optical components wherein heat is
generated within said
cabinet, said apparatus comprising: a heat exchanger having internal and
external chambers
surrounding heat pipe coils, said heat exchanger attached to said analyzer
cabinet; said internal
chamber being in communication with said cabinet by means of an inlet and an
outlet; a
continuously operating constant speed fan located in said inlet for
circulating air past said coils
and through said cabinet; said external chamber being in communication with
fresh outside
ambient air; and a variable speed fan circulating outside ambient air through
said external
chamber; a temperature sensor located in said cabinet on the critical optical
components within
said analyzer cabinet; said sensor producing signals corresponding to the
temperature at the
sensor location; and said variable speed fan being responsive to said signals,
2, The apparatus of claim 1, wherein the critical optical components are of
the group
consisting of a photodetector, a grating, and a grating mount.
3. In the process for controlling at an aim point within plus or minus
0.1°C the internal
cabinet temperature of a near-infrared analyzer having critical optical
components housed within
a cabinet wherein a heat exchanger having internal and external chambers
surrounding coils
attached to the analyzer cabinet, the internal side of the chamber in
communication with the
cabinet via an inlet and outlet wherein a continuously operating constant
speed fan circulates air
past the coils and through the chamber and the external chamber communicates
with fresh,
outside ambient air via an inlet and outlet having a variable speed fan, the
improvement
comprising:
(a) continuously measuring the temperature of the critical optical components
in
cabinet by means of a temperature sensor fastened to the critical components;
and
(b) continuously circulating temperature-controlled air by means of the
constant
speed fan past the critical optical components to maintain the components at a
relatively constant temperature;


6


(c) controlling the speed of the variable speed fan from signals generated by
the
temperature sensor.
4. The process of claim 3, wherein the critical optical components are of the
group
consisting of a photodetector, a grating, and a grating mount.

Description

HT-340D 2 i 96758 ''ro.~-°s96
Temperature Control of Near-Infrared Analyzer -
.S ~ $dCkgT'O and O 11e T V T~ ~ OI1 ._
The invention relates to thermal management in
ir_strumentation and more particuharly it relates to
temperature control of a-near-infrared analyzer.
Thermal management-in instrument packaging has always
been an impcrtant design consideration. Internal
temperature control or near-infrared (NIR? analyzers is-
essential for measurement precision. More particularly,
NIR spectrophotometers- can be affected by temperature
variations as little as 2.to 4degrees C, which cause
shifting of optimal wavelengths, and the addition of error -
in the measurement.
The typical process spectrophotometer is controlled
within.a band cf temperature by utilization of an on-off
type control strategy. In the "on" state, a condenser or .__. -
other device is turned on to remove heat build-up from
within the spectrophotometer enclosure as is described in
U.S. Pater_t No. 4,328,676. The condenser or other device
remains "on" until a low temperature limit is reached anal
then the condenser is turned "off." The-temperature in -
the spectrophotometer enclosure rises from the heat
generated by the electronics and/or tile external
environment until a second temperature limit is reached,
which causes the condenser or other device to be turned -
"on" again. This on/off temperature control approach
commonly al7.ows the internal temperature to cycle 2-~ C
degrees..
SLT~!aZ'V of th Tnvon t i nn
A preferred temperature control strategy was devised
to remove heat from the analyzer and control the optical
bench temperature continuously at aim. A temperature
sensor is fastened to the optical bench in an analyzer to
serve as a measurement input device for a control strategy
which is truly aim-seeking.- The control strategy employs
w heat pipe heat exchanger to remove heat from the
1
F~Ai~~,7~~ ~H~Gi




WO 96105545 , 219 6 7 5 8 PGTIUS95I08968
analyzer enclosure. A heat pipe utilizes a fluid (such as
an alcohol) to remove heat by evaporation of the fluid at
an internal air circulation heat exchanger and then
recondensing the fluid at an external air circulation heat
exchanger. Heat pipes are particularly useful in that
internal cabinet air, not outside air, is circulated
through the critical optical components, thereby ,
eliminating the need for additionalfiltering of the
cooling air.
A PID temperature controller achieves the desired
temperature setpoint by manipulation of heat exchanger fan
speeds. The heat removal rate can be very precisely
controlled..,T~ practice, both heat exchanger fans could
be controlled._together; however, to,achieve optimal
internal temperature uniformity, the internal heat
exchanger fan-is maintained at full speed and just the
external fan is controlled to adjust heat removal rate.
Optical-bench temperature control is maintained to plus or
minus 0.1 degree C vs. a typical temperature control range
of plus or minus 2 degrees C.
More particularly, the invention includes an
apparatus and-a process for controlling the temperature of
an analyzer cabinet wherein heat is generated within the
cabinet. The apparatus comprises a heat exchanger having
internal and external chambers surrounding heat pipe coils
attached to the analyzer cabinet. The internal side
chamber is in. communication with the cabinet via an inlet
and an outlet; a continuously operating constant speed fan
located in the inlet is provided for circulating air past
the coils and through said cabinet. The external chamber
is in communication with fresh outside ambient air and a
variable speed fan circulates outside ambient air through
the external chamber. A temperature sensor located in the
cabinet produces signals corresponding to the temperature
t
at the senso~ocation. The variable speed fan is
responsive to-.the signals produced,by the sensor.
The other. embodiment of this invention is an improved
process for controlling the internal cabinet temperature
of a near-infrared analyzer, and therefore, the-accuracy
:_il., :,"',.a!'., i_ r-yi i !°1.'tu r.. ~ 2



~WO 96105545 , 219 6 l 5 8 PCTIUS95108968
of the analyzer. This improvement comprises continuously
measuring thetemperature of the critical optical
components in the cabinet, and, in response, continuously
circulating temperature-controlled air by these critical
optical components to maintain the components at a
relatively constant temperature. By use of this process,
v the temperature of the temperature-sensitive critical
optical components can be maintained to plus or minus O.I
degree C.
Brief Description of the Drawing
The Figure is a schematic illustration of an analyzer
and associated internal and external heat exchangers. -
Detailed Description of the Preferred Embodiment
Referring to the Figure analyzer, cabinet 10 contains
critical optical systems 12, in addition to electrical -
components (not shown). "Critical optical systems" or
"critical optical components' are meant to include
photodetectors, gratings, grating mounts, etc., which are
temperature sensitive and are normally housed inside the
analyzer cabinet in what is called an "optical bench."
Temperature sensor 14 is attached to the critical optical
systems and outputs a temperature signal to temperature -
controller 15. Also,-attached to analyzer cabinet 10 is a
heat pipe heat exchanger 16, having an internal side 16a,
an external side 16b, and heat pipe coils 18. The heat
pipe coils extend from the internal side to the external
aide so that heat may be transferred from the internal
side to the external side. In addition, the internal side
has an internal inlet 20 for removing air from the
analyzer cabinet, and an internal outlet 22 for providing
temperature-controlled air to the critical optical
systems. A continuously operating internal fan 24 is
mounted in the internal outlet 22 to provide movement of
air through the internal side of the heat pipe heat
exchanger. The external side 16b of the heat pipe heat
exchanger has an external inlet 28 for providing fresh
outside ambient air to the heat-pipe heat exchanger, and
3




VI'O 96105545 _ 219 6 7 5 8 PC1YU595I08968
an external outlet 30 for removing this air from the
external side_ A speed-controlled fan 32 is mounted in
the external outlet 30 to provide movement of air through
the external side of theheat pipe heat exchanger 16. The
v
speed controlled fan 32 is electrically connected to the S
temperature controller 15, and the speed of the fan
increases or decreases based on the output signal from the ,
temperature sensor 14, thus providing more or less cooling
to the heat pipe coils 18 in heat exchanger 16.
In one example of a preferred construction, a Noren
Model CC600F heat pipe heat exchanger containing interior
and exterior fans (supplied by Noren Products, Inc., Menlo
Park, CA) was attached to the enclosure of a Guided Wave
300P Near-Infrared Analyzer- (supplied by UOP Guided Wave,
I5 E1 Dorado Hills, CA). A Minco foil-type 100 ohm
Resistance Temperature Detector, or RTD, was attached to
critical optical components in the analyzer and inputted
signals to a ECS Model 6415 PID temperature controller
having a 10 amp control output. This output was in turn
connected to the external fan of the heat pipe heat
exchanger for;control of the external fan speed.
4

Representative Drawing