Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Reexamination Certificate
1999-10-26
2001-09-25
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
C374S185000, C340S870170
Reexamination Certificate
active
06293699
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for continuously monitoring temperatures at multiple locations within a controlled temperature unit (CTU). The instant invention provides the advantage that the temperature probes used to acquire the data may be easily removed for good manufacturing practice (GMP) compliant calibration, and most importantly without disturbing the contents of the CTU.
CTUs are employed in a variety of applications. They are routinely used in stability studies as a part of drug development and manufacturing programs as well as storage of GMP raw materials, retain samples and bulk intermediates. Central to such programs is adherence to GMP requirements, which present an industry standard for manufacture. Compliance to good manufacturing practices requires regular calibration of CTUs to ensure proper operation of the unit.
Continuously monitored CTUs typically measure temperature by means of a thermocouple or RTD (Resistive Temperature Device). However, there is no commercially available CTU design which incorporates removable temperature sensor wiring or a thermocouple unit in order to provide both continuous acquisition and output of the data in a format able to be manipulated by computer software. The few CTUs that do have devices that output data to a computer are not able to be externally calibrated without disturbing the contents of the CTU or are only equipped to monitor a single heating or freezing element and not multiple locations within the CTU over the course of long term storage of samples. None of these CTUs has a removable RTD assembly to permit easy calibration. U.S. Pat. No. 4,776,705, discloses a device that permits the determination of temperature in hostile environments such as a high-temperature reactor. This device utilizes a removable thermocouple, however,the apparatus primarily addresses the problem of breakdown of the wires of the thermocouple due to interaction with the products of combustion of carbonaceous fuel. Similarly, U.S. Pat. No. 4,510,343 discloses a device to be used in petroleum cracking furnaces.
Both of these prior art devices are manufactured using a refractory material, typically a metal or ceramic, and neither of these devices has been employed in subfreezing conditions. These refractory materials maintain their integrity under high heats, but under freezing conditions, devices employing this construction run the risk of having the interior RTD freeze in place thereby effectively becoming irremovable. These devices have the potential for moisture accumulation as a result of incident air condensing on the RTD when it is removed from its seated position, resulting in freezing inside the thermowell.
In order to circumvent this problem, workers in the industry have resorted to inserting thermocouple wiring through the door gasket of a CTU requiring continuous observation. However, these wires must be removed from the CTU in order to calibrate them. Even careful removal of the wires, can lead to disruption of the contents of the CTU which, in addition to general inconvenience, may be fatal to long term stability studies requiring undisturbed incubation of samples for long periods of time. Replacement of the wires in identical locations is also difficult, and therefore a long-term assessment of temperature variation from a given probe is virtually impossible. The present invention solves this industry-wide problem.
Thus, the primary object of the instant invention is to provide a method for continuously monitoring temperature wherein the RTDs used in data acquisition may be easily removed for calibration without disturbing the contents of the CTU.
SUMMARY OF THE INVENTION
There is disclosed a method for continuously monitoring a CTU using an apparatus that is easily removable for calibration, without disturbing the contents of the CTU. The invention overcomes the problems of inconsistent replacement of the probe wires and load disruption. The method comprises the placement of polytetrafluoroethylene (PTFE)-coated sleeves into holes piercing the thickness of the walls of the CTU at minimally six different points per 1200 cubic feet of CTU volume. RTDs are then inserted into the sleeves. The RTDs are functionally attached to data collection means such as the module produced commercially by Keithley Corporation under the trade name SMARTLINK™. The data module is functionally attached to an ethernet port using a standard interface cable which allows temperature data to be transmitted over a network to data acquisition means, such as a desktop or laptop computer. Data analysis software installed on the data acquisition means permits the operator to manipulate the data and store it or output it in a graphical, tabular or text format. The semi-permanent placement of the RTDs permits their easy removal from the PTFE-coated sleeves for calibration purposes and permits them to be reliably replaced in the same positions in order to impart overall uniformity to the data acquired, and the ability to collect long-term temperature data from consistent locations within the CTU.
The instant invention will be more fully understood in the following detailed description, it being understood, however, that the invention is not confined to the precise disclosure. Changes and modification may be made that do not affect the spirit of the invention, nor exceed the scope thereof, as expressed in the appended claims. Accordingly, the instant invention will now be described with particular reference to the accompanying drawings.
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Noel Fenton, “Remote Temperature Measurements”, Instruments and Control Systems, vol. 43, No. 6, pp. 96-97, Jun. 1970.
Bailey Fred J.
Holz Carl W.
Pinder Mark
Daniel Mark R.
Gutierrez Diego
Hunter, Jr. James M.
Merck & Co. , Inc.
Pruchnic Jr. Stanley J.
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