United States Patent
`Hinman
`
`[191
`
`3,863,049
`1111
`1451 Jan. 28, 1975
`
`[54] TEMPERATURE CONTROL APPARATUS
`_
`ngsYggfmucAL TYPE CHEMISTRY
`A
`Inventor: Clyde D. Hinman, Wilton‘ Conn,
`[75]
`[73] Assignee: Union Carbide Corporation. New
`York. NY-
`[22]
`Filed:
`May 31 1972
`[21] Appl. No.: 258,259
`
`[52] US. Cl.................. .. 219/389, 165/39, 219/370,
`219/441, 219/494, 233/“
`Int. Cl. ......................... F27b 7/00, F27d 11/02
`[51]
`Field of Search ........." 219/370, 385, 388’ 389,
`[58]
`219/400, 413, 430’ 441, 494., 34/8, 58’ 59;
`165/39; 233/11
`
`[56]
`
`2,742,190
`
`References Cited
`UNITED STATES PATENTS
`6/1973 Glam ................................ .. 219/389
`
`2.768.546
`3,246,688
`3,322,338
`3,529,358
`3,566,070
`
`Shipes ................................. .. 165/39
`10/1973
`4/1966 Colburn .............................. 1. 165/39
`5/1967
`Stallman et al. ...................... 233/23
`9/1970
`Robinson ...................... .. 219/400 x
`2/1971
`Pesgzlt ............................. 219/388 X
`
`Primary Examiner—Volodymyr Y. Maycwsky
`Almrncy, Agent, or Firm—Frederick J. McCarthy
`
`1571
`
`ABSTRACT
`
`,
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`A temperature control apparatus for raising and con-
`trolling the temperature of small volumes of liquid by
`heating the liquid and detecting the instantaneous
`temperature and rate of temperature increase and uti-
`lizing this information to control the heating of the liq-
`uid so that the desired liquid temperature is attained
`and maintained in a minimum time interval.
`
`4 Claims, 5 Drawing Figures
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`1
`TEMPERATURE CONTROL APPARATUS FOR A
`CENTRIFUGAL-TYPE CHEMISTRY ANALYZER
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`3,863,049
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`2
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`The present invention is directed to an improved
`temperature control system. More particularly,
`the
`present invention is directed to a temperature control
`system for controlling the temperature of small vol—
`umes of liquid undergoing analysis in a centrifugal-type
`chemistry analyzer.
`,
`Centrifugal-type chemistry analyzers, such as the
`type disclosed in
`“Analytical Biochemistry",
`28
`545—562 (1969) introduce by centrifugal force small
`volumes of liquid sample and reagent, e.g., a combined
`volume of 300—600 milliliters into a series of cuvettes
`arranged around the periphery of a rotor. The reaction
`in the cuvettes is monitored with precision by photo-
`metric means. The reactions involved are usually tem-
`perature sensitive, with a constant temperature in the
`range of 25° to 40°C being usually required. Since the
`liquids involved in the tests are rarely at the desired
`temperature to begin with, and often are under refrig-
`eration until just prior to testing, it is important that a
`system be provided for raising and controlling the tem-
`perature of the liquids involved. Also, since most of the
`reactions involved in the use of centrifugal analyzers
`proceed rapidly, it is important that the temperature of
`the test liquid be brought rapidly, e.g., within about 30
`to 40 seconds, to the desired value and held closely at
`this value throughout the testing period.
`It is therefore an object of the present invention to
`provide a system for raising and accurately controlling
`the temperature of small volumes of test liquids in a
`centrifugal-type chemistry analyzer.
`Other objects will be apparent from the following de-
`scription and claims taken in conjunction with the
`drawing wherein:
`FIG. 1 is a sectional elevation veiw of a centrifugal
`type analyzer,
`FIG. 2 is a plan view of the analyzer of FIG. 1 show-
`ing means for applying heated air to the analyzer,
`FIG. 3 shows a series of curves representing various
`heating conditions in an analyzer of the type illustrated
`in FIG. 1,
`FIG. 4 shows a block diagram of the temperature
`control system of the present invention and,
`FIG. 5 shows a specific embodiment of a temperature
`control system in accordance with the present inven-
`tion. With reference to the drawing FIG. 1 shows in ele-
`vation a centrifugal—type analyzer comprising a remov-
`able sample-reagent disc 10 supported on a rotor 11
`and indexed theretoby pin 14. Rotor 11 is affixed to
`drive assembly 12 by pin 15. Drive assembly 12 is rotat—
`ably driven by way of v-belt pulley 13 attached to drive
`shaft 17. The portion 16 of rotor 11 is suitably of stain-
`less stell over which is arranged a glass plate 18. The
`body portion 20 of sample-reagent disc 10 is suitably
`formed of Teflon* and contains a plurality, usually
`about 30, of concentrically arranged inter-connecting
`cavities indicated at 22. Reagent cavity 24, contains for
`example a glucose reagent such as a 0.3 molar trietha—
`nolamine buffer of pH 7.5 containing 0.0004 Mol/liter
`NADP, 0.0005 MOI/liter ATP, 70 mg/liter hexokinase,
`140 m'g/liter glucose-6-phosphate dehydrogenase and
`0.004 Mol/liter MgSO4. The reagent, indicated at 26,
`upon spinning of the sample-reagent disc 10‘, passes
`into sample cavity 28, containing for example blood
`serum, and both liquids pass via transfer passage 30
`
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`into cuvette 32 located in ring member 34 which is af-
`fixed at 31 to rOtor ll. Cuvette 32, and all other cu—
`vettes, are enclosed by ring member 34 and are in that
`transfer relation therewith. Ring member 34 is formed
`of aluminum, coated for corrosion resistance purposes
`with a thin layer of Teflon* 35 in which is mounted a
`temperature sensing element, e.g., a thermistor, indi-
`cated at 36 which is adapted to provide an electrical
`signal indication of the temperature of the liquid in cu~
`vette 32. Cuvettes 32 are also provided with a thin Tef-
`lon* coating 33 for purposes of corrosion resistance.
`The extent of the reaction between the liquids in cu-
`vette 32 is measured photometrically by means of light
`source 38 and photomultiplier 40. The electrical signal
`derived from thermistor 36 is conducted via wire leads
`40 to slip rings 41 and to brushes 44 from which the sig’
`nal is conducted by wires 46 to the temperature con-
`trolling circuit illustrated in FIGS. 4 and 5 hereinafter
`more fully described.
`*Trademark of El. duPont de Nemours
`As shown in FIG. 1, the reaction in the cuvettes will
`take place within a substantially confined space'en—
`closed by metal housing 48, plastic ring shield member
`50 and plastic cap member 52. This arrangement essen-
`tially separates the interior of the housing from the out-
`side ambient temperature conditions. Hot air, con-
`trolled by the circuit of FIGS. 4 and 5 is introduced into
`the confined reaction environment at opening 54 and
`exits through openings 56 in housing 48. The general
`heating arrangement
`is illustrated in FIG. 2 which
`shows schematically a conventional blower motor and
`blower unit 60 which forces air over heating element
`62 through duct 64 and into housing 48.
`’
`With reference to FIG. 3 of the drawing, this Figure
`shows a series of curves, obtainable using a conven-
`tional “Brush” millivolt recorder which relate to the
`raising of the temperature ofa liquid in a cuvette 32 to
`a desired temperature. Curve A represents the charac—
`teristic variation of temperature with time in the cu-
`vette upon introduction of cold liquid into the cuvette
`without any heat being added. This characteristic varia-
`tion is obtained in the practice of the present invention
`due to the fact that the cuvette is located in a member,
`i.e., aluminum ring member 34, which has a substan-
`tially larger thermal mass than the liquid in the cuvette
`and is at the desired reaction temperature. Ring mem-
`ber 34 can be quickly raised to the desired reaction
`temperature simply by actuating the control circuit
`without any liquid in the cuvettes. The heat stored in
`the ring member is conducted to the liquid in the cu-
`vettes causing the cuvette temperature to rise as gener-
`ally indicated by curve A. The temperature control sys—
`tem of the present invention is most effective, if the'
`temperature of the liquid in the cuvettes be raised,
`without the direct application of heat, from an initial
`“cold” condition in the range of about 15°C to 20°C,
`to within 04° to 08°C of the desired value in the range
`of about 25°C to 40°C, within 20 to 40 seconds. This
`can be readily provided through the use of a metal ring
`member 34 having a thermal mass of about 5 to 20
`times or more of the thermal mass of the total liquid in
`the cuvettes. Aluminum is preferred for the ring mem-
`ber 34 because of its high heat conductivity although
`generally all structural metals and high heat conducting
`materials can be used. By way of example, the thermal
`mass of a 1 kilogram aluminum ring member would be
`1,000 X 0.23 (the specific heat of aluminum) or about
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`3
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`3,863,049
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`4
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`230. The thermal mass of 12 grams of reagent plus sam-
`ple (95 percent or more water) would be 12 X 1 (the
`specific heat of water) or about 12. The ratio of the
`thermal mass of the ring to the liquid would be about
`20. A ring member of about 2,500 grams of copper
`would provide about the same ratio. Care should be
`taken in coating the cuvette with any substance that in-
`troduces significant thermal resistance between the liq-
`uid in the cuvette and the ring member so that the de-
`sired temperature increase is not unduly delayed. For
`example, a 3—7 mil Teflon“ coating has been found to
`be satisfactory where a ring to liquid thermal mass ratio
`of about 20 is provided. Referring further to FIG. 3, at
`time T, the temperature in the empty cuvette is the de-
`sired value, e.g., 30°C. The temperature in the cuvette
`is initially at the desired value, e.g., 30°C, due to prior
`heating of ring member 34 with hot air from the heater
`unit illustrated in FIG. 2. When cold liquid fills the cu-
`vette the temperature drops rapidly and then, on ac-
`count of the heat stored in the relatively larger rotor
`mass, and the small liquid volume in the cuvette, the
`temperature fairly rapidly rises. However the tempera-
`ture in the cuvette will never get within a tolerable
`value of the desired temperature, e.g., i0.1°C, indi-
`Cated at 100 without the addition of heat.
`‘Trademark of El. duPont de Nemours
`If excess heat is rapidly and continuously applied to
`the enclosed cuvette system from time T. to T2, the
`temperature-time relationship will be generally as indi-
`cated in curve B, i.e., the desired temperature will be
`reached rapidly and then exceeded by an undesirably
`large amount and will “over shoot” requiring a rela-
`tively long time to return to within an acceptable toler-
`ance of the desired value as indicated at T3. If, on the
`other hand, insufficient heat is applied, the situation
`approaches the condition of curve A.
`The desirable situation is illustrated by curve C when
`the temperature rapidly reaches the desired value and
`where any “over shoot” is within the acceptable toler-
`ance, e.g., about 01°C.
`This is accomplished in the present invention by the
`arrangement illustrated in FIGS. 4 and 5. With refer-
`ence to FIG. 4, the output voltage signal from the eu-
`vette thermistor 36 is applied to a standard bridge cir—
`cuit 100 having adjustments 101, 103 and 105 whereby
`the bridge circuit 100 will indicate a “zero” value when
`the signal from thermistor 36 corresponds to the pre-
`set desired temperature, e.g., 30°C. In the case where
`a cold sample is introduced into the cuvette, the signal
`from thermistor 36 will cause the bridge 100 to be un-
`balanced and a signal proportional to the temperature
`difference, indicated at 135, will be applied to amplifier
`110 to actuate trigger unit 120. Pulses from the trigger
`unit 120 are applied to a power switch 130 which per-
`mits alternating current power to be applied to how air
`heater 140 so long as pulses are received from trigger
`unit 120. The hot air from heater 140 is directed to the
`cuvette rotor assembly as previously described to raise
`the temperature in the cuvette. When the “no added
`- heat” profile (curve A) of the unit is approximately
`known as shown in FIG. 3, an initial “hold off" temper-
`ature can be estimated. This “hold off” temperature
`can be initially selected as about one half the total tem—
`perature drop, indicated at 145 in FIG. 3. This “hold
`of ” may be on the order of 2°C. With the approximate
`“hold off” value determined, “hold off” circuit 150 is
`set so that the output of rate limiter circuit 160 is iso-
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`Page 8 of 10
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`lated from the trigger circuit 120 by gate 165 for as
`long as the temperature in the cuvette is below the set
`“hold off" temperature. Under these circumstances,
`the signal from bridge 100 is applied via amplifier 110
`to trigger circuit 120 and heater 140 supplies heat to
`the cuvette containing ring member 34. When the tem-
`perature in the cuvette raises to the “hold off" level,
`the output of rate limiter circuit 160 will be applied to
`trigger circuit 120 by the closing of “hold off” gate
`165. Rate limiter circuit 160 detects the increase in
`rate of the output of amplifier 110, i.e., the rate of tem-
`perature increase in the cuvette. If the rate of tempera—
`ture increase is too fast, as compared to a predeter-
`mined value, i.e., an “over shoot" will eventually occur
`unless heating is discontinued, and under these condi-
`tions, a signal from the rate limiter circuit 160 “turns
`of ” the trigger circuit 120. Heat is no longer applied
`to the rotor assembly until the rate of temperature in-
`crease falls below the desired predetermined value, at
`which time the signal of rate limter 160 is no longer ap-
`plied to trigger circuit 120 and heat is again supplied to
`the rotor assembly. This operation continues until the
`desired temperature is reached and “zerO” output is
`present at bridge 100. The desired pre—selected rate of
`temperature increase to provide a temperature profile
`as indicated at “C” can be obtained by trial and error.
`Also, this rate can be initially approximated by obtain-
`ing a “no heat added” profile, such as curve A and
`marking off an increment equal to the maximum per—
`missable temperature tolerance, e.g., 01°C, as indi-
`cated at 115. The corresponding slope on curve A, in—
`dicated at 167, can serve as a first approximation of the
`maximum desired rate.'Further routine adjustment of
`the rate limiter circuit will optimize the heating cycle.
`In the event that with the initial “hold off" setting, the
`rate limiter circuit 160 never “turns on,” i.e., the maxi-
`mum desired slope is always exceeded,
`then lower
`“hold off” settings should be successively applied until
`the rate limiter circuit 160 becomes operative. The
`maximum rate setting can then be adjusted to minimize
`the time T4 required to reach an acceptable tempera-
`ture. For most tests using a centrifugal photometric an-
`alyzer, this time should be less than thirty to forty sec-
`onds.
`’
`With further reference to curve C of FIG. 3, illustrat-
`ing a temperature curve where temperature control is
`provided in accordance with the present
`invention,
`continuous hot air is supplied in the interval T. to T,'.
`Hot air is then turned off until the slope of curve C de-
`creases at 490 to just below the maximum desired slope
`500. Rate Limiter circuit 160 then causes hot air to be
`re-applied and the maximum desired rate of tempera-
`ture increase is essentially maintained until the desired
`temperature is achieved at 510, at which time the con-
`trol system is “off” since the voltage at the output of
`bridge 100 is “zero.” The cuvette temperature will then
`“over shoot” only within the desired tolerance. In the
`event that curve C goes below the desired tolerance at
`520 a signal will be developed at bridge 100 and trigger
`circuit 120 will cause heat to be re—applied and the tem-
`perature will be maintained within the desired toler~
`ance.
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`FIG. 5 illustrates more specifically the system of FIG.
`4. With reference to FIG. 5 the output of cuvette ther-
`mistor 36 is applied via slip rings 42 to bridge circuit
`100 which,
`in addition to thermistor 36, comprises
`fixed resistors 300 and 302 and the conventional ad-
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`justable resistor arrangement which includes fixed re-
`sistors 306, 308 and 310 and adjustable resistors 312,
`314 and 316. Switch 318 is positioned to select the
`temperature value at which the bridge output will be
`“zero,” i.e., balanced, for the desired cuvette tempera-
`ture. For example, if the desired cuvette temperature
`is to be 30°C, switch 318 is placed in that position and
`a temperature of 30°C established in the cuvette. Ad-
`justable resistor 314 is then varied until the bridge out-
`put at 320, more practically, the amplifier output at
`340, is “zero.” The bridge circuit 100 is thus calibrated
`for a desired cuvette temperature of 30°C. The bridge
`can be similarly calibrated for other desired cuvette
`temperatures. The output of bridge circuit 100 is ap—
`plied to amplifierillo, for example a commercial dif-
`ferential amplifier Such as Fairchild ,u A 725. Custom-
`ary +15 VDC and -15VDC supplies to amplifier 110
`are provided at 322 and 324 respectively. A~conven—
`tional feedback circuit 326, c0mprising resistor 328
`and capacitor 330, is provided together with a conven-
`tional temperature balancing resistor 334. The output
`of amplifier 110 appears at resistor 338. By way of ex-
`ample, if the output of bridge circuit 100 is 0.02 volts
`for each degree Centigrade that the cuvette tempera-
`ture is below the desired temperature (which can be
`determined by routine calibration) amplifier 110 will
`provide an increased signal, e.g., 1 volt per degree Cen-
`tigrade, depending on the amplifier gain. Under these
`exemplary circumstances, if upon introduction of cold
`test liquid into the cuvette, the temperature drops from
`its initial value of 30° to 20°C, an output signal of 10
`volts will be provided at location 340 at the output of
`amplifier 110. This signal is applied at the input 342 of
`trigger circuit 120 and the input 344 of “hold off" cir-
`cuit 150. As shown in FIG. 5. “hold off” circuit 150
`comprises amplifier 344, which can be a commercial
`differential amplifier such as Fairchild u A741, which
`is provided with +15 volts and -15 volts at 346 and
`348. A reference voltage input signal for “hold off”
`amplifier 344 is provided by way of adjustable resistor
`350 and fixed resistor 352 supplied with +15VDC as
`indicated at 354. This reference signal from adjustable
`resistor 350 is the “hold off” signal. For example, if as
`previously noted, the desired cuvette temperature is
`30°C, and the cuvette temperature falls to 20°C upon
`introduction of cold test liquid, the “hold off” voltage
`at adjustable resistor 350 can be set to 5 volts as a first
`approximation, if the output of amplifier 110 is 1 volt
`per degree centigrade, as previously given by way of ex-
`ample. Under these circumstances, as long as the out-
`put of bridge amplifier 110 is more than 5 volts, a signal
`is provided at the output of “hold off” amplifier 344
`which, due to gate arrangement 165 (comprising di-
`odes 353 and 355), prevents an inhibiting signal from
`passing from rate limiter circuit 160 to trigger circuit
`120. Consequently, the signal from bridge amplifier
`110 is applied to trigger circuit 120 at 342, and causes
`electrical pulses to be applied to power switch 130
`whereupon AC power is passed through heater element
`62 of air heater 140 and hot air is delivered to the en-
`closure surrounding the cuvette as previously de—
`scribed, whereby the cuvette temperature is increased.
`Trigger circuit 120 can be a commercial unit such as
`Fairchild ,u A 742 and is arranged to receive an AC ref-
`erence signal at 356 by way of transformer 359, and
`DC power at 358 through the arrangement comprising
`resistors 360 and 362, diode 364 and filter circuit 366.
`
`With a positive signal applied to the trigger circuit 120
`at 342, output pulses appear at 367 and are applied via
`transformer 370 and power switch 130 to heater ele-
`ment 62 until an inhibiting signal, e.g., 15 volts DC is
`applied at 368.
`,
`Such an inhibiting signal will be applied when the
`output of bridge amplifier 110 increases greater than
`the pre-set rate of voltage increase due to the heating
`of the cuvette by hot air supplied from air heater 140.
`At this time, gate 165 will “open,"* permitting the sig-
`nal at the output 370 (if a signal is present) to be ap-
`plied at the input 368 of trigger circuit 120 which
`“turns off" the trigger circuit 120 discontinuing the ap-
`plication of hot air to the cuvette. Whether an inhibit-
`ing signal is present at the output 370 of the rate limiter
`circuit 160 depends on the rate of increase of the out-
`put signal of bridge amplifier 110 (which is propor-
`tional to the rate of temperature rise in the cuvette)
`and the desired maximum rate of cuvette temperature
`increase, determined for example in the manner previ-
`ously described in connection with FIG. 3. The rate of
`increase for the output signal of bridge amplifier 110 is
`detected by a conventional derivative circuit 372 com-
`prising capacitor 374 and resistor 376. The derivative,
`or rate signal obtained is applied at 378 to amplifier
`380, which can be a commercial differential amplifier
`such as Fairchild p.A74l. Amplifier 380 also receives a
`reference signal at 382 from temperature compensat-
`ing resistor 382, which corresponds to the desired max-
`imum rate and is set by adjustment of variable resistor
`384. For example, if the maximum desired rate of tem-
`perature increase is 0.01°C/second, the pre-set voltage
`at 382 would, neglecting off—set in amplifier 380, be
`0.88 millivolts for a typical value of 22K ohms for resis-
`tor 376 and 4 microfarads for capacitor 374. Any off-
`set in amplifier 380 can be taken care of by adjustment
`of variable resistor 384. For as long as the voltage at
`378 is larger in magnitude (more negative) than this
`value (0.88 mv) i.e., the rate of temperature increase
`is above the desired maximum, the output of amplifier
`380 is a positive signal, e.g., +15VDC, and an inhibiting
`signal is appliedvia gate 165 to trigger circuit 120 and
`heater unit 140 will be inactive. When, however, the
`voltage at 378 is lower than the pre—set value (0.88 mv)
`i.e., the rate of temperature increase is below the de-
`sired pre-set value, the output of amplifier 380 be-
`comes negative and this signal is blocked by diode 355
`whereupon trigger circuit 120, and hence heater unit
`140, is activated to supply additional hot air to the eu-
`vette and raise the temperature at a faster rate. This
`procedure then continues until the desired cuvette tem-
`perature is reached, e.g., 30°C, at which time the out-
`put of bridge amplifier 110 is “zero” and circuit opera-
`tion ceases.
`*(i,e., close the circuit)
`If it is desired to further reduce the time required to
`reach the desired cuvette temperature, the'pre-set rate
`voltage at 382 can be gradually increased while avoid-
`ing an undesirable temperature “over shoot."
`In the event that, with the initial estimated pre-set
`“hold off" voltage, the inhibiting signal of the rate lim-
`iter amplifier 380'is never applied to trigger circuit 120,
`i.e., the rate limiter never “cuts in,” the likelihood is
`that the “hold off" signal at 350, at the input to ampli-
`fier, is too small in magnitude and should be gradually
`increased in magnitude until the rate limiter 160 “cuts
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`in" at least once before the desired temperature is
`reached.
`'
`By way of example, in the operation of a particular
`embodiment of the present invention the cuvette con-
`taining ring member (containing 30 cuvettes having a
`volume 0.45 to 0.6 milliliters each) was formed of an
`aluminum ring (cross section of approximately l%%in-
`ches X + inches) having an inner diameter of 5 1/2 inches
`and an outer diameter of 8% inches. The weight of the
`ring member was about ‘1 kilogram and the effective
`heat transfer area was 30—35 inz. The outer surfaces of
`the aluminum ring member, and also the inner cuvette
`surfaces, were coated with a layer of Teflon about 3—9
`mils thick. The aluminum ring member was located in
`an aluminum housing similar to the arrangement shown
`in FIG. 1. The outer diameter of the housing formed of
`Va inch aluminum was approximately. 10 inches and the
`height was about 6—7 inches. The housing was affixed
`to a base plate of 1/2 inch thick aluminum. The top of
`the housing was essentially closed by plastic members
`made of polystyrene. The ring member and sample-
`reagent disc were rotated at 1,000 RPM and the 30 cu-
`vettes were each filled with about 0.4 milliliters of sam—
`ple and reagent at a temperature of 15° to 20°C so that
`a total of about 12 grams of liquid was introduced into
`the cuvette containing ring member. Since the liquid
`was 95 percent or more H20, this is the thermal equiva—
`lent of about 12 grams of water. The aluminum cuvette
`containing ring member was initially at a temperature
`of 30°C, due to previous heating, which was the desired
`cuvette reaction temperature. Heated air was available,
`through a duct arrangement as indicated in FIG. 1, at
`about 65°C and 20 cubic feet per minute from a heater
`unit controlled by the system of the present invention.
`The desired reaction temperature of 30° C was reached
`within about 30 seconds and maintained within : 01°C
`by the action of the control system of the present inven-
`tion.
`The temperature control system of the present invenv
`tion has a high degree of flexibility. For example, with
`the system adjusted to provide a cuvette temperature
`control as indicated in curve C in FIG. 3, for the largest
`and coldest liquid sample to be handled by the centrifu-
`gal analyzer, smaller and less cold samples will be
`raised to the desired temperature (and maintained at
`this temperature) within the required time without any
`need for further adjustment of the system. Such smaller
`and less cold samples are indicated as curves D and E
`in FIG. 3. For curve D, heated air will be initially con-
`tinuously supplied for only the relatively short interval
`d after which heat control is provided by operation of
`
`the rate limiter circuit 160 in the manner previously de-
`scribed. For curve E, initial continuous heating will not
`be provided and heat control will be provided only by
`operation of rate limiter circuit 160. Of course, if de-
`sired, optimization of time required to raise the D and
`E type samples to the desired temperature can be
`achieved following the procedure previously described.
`I claim:
`1. A temperature control apparatus comprising a
`metal base member; a plurality of chambers adapted to
`contain liquid located within said base member in heat
`transfer relationship therewith, the thermal mass of the
`base member being substantially larger than the ther-
`mal mass of the thermal mass of liquid contained in the
`chambers; housing means substantially enclosing the
`base member and chambers to separate the base mem-
`ber and chambers from ambient temperature; a heating
`element adapted to develop heat by the passage of elec-
`trical current therethrough, means for passing air in
`contact with the heating element for the heating of said
`air and for introducing the heated air into the housing
`member to transfer heat developed in the heating ele—
`ment to the base'member and chambers to raise the
`temperature thereof to a desired value; temperature
`sensing means adapted to provide an electrical signal
`proportional to the amount by which a selected cham-
`ber is below the desired value; control means respon-
`sive to the signal of the temperature sensing means
`adapted to supply electrical energy to the heating ele-
`ment; rate detecting means for obtaining an electrical
`signal proportional to the rate of temperature increase
`of the selected chamber and for applying such electri—
`cal signal to the control means to inactivate the control
`means when the rate of temperature increase is above
`a predetermined value; means for preventing the signal
`from the rate detecting means from inactivating the
`control means as long [as the temperature of the se-
`lected chamber is below a predetermined value.
`2. An apparatus in accordance with claim 1 wherein
`said base member is formed of aluminum.
`3. An apparatus in accordance with claim I wherein
`chambers are enclosed within the base member and the
`thermal mass of the base member is at least about 5
`times the mass of liquid in the chambers.
`4. An apparatus in accordance with claim 1 wherein
`the chambers are enclosed within said base member,
`the base member is formed of aluminum, and the ther-
`mal mass of the base member is about 20 times the
`thermal mass of the liquid in the chambers.
`*
`*
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`*
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`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`(15
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