Automatic temperature and humidity regulation – Motors – Electric
Reexamination Certificate
1998-12-18
2001-01-16
Wayner, William (Department: 3744)
Automatic temperature and humidity regulation
Motors
Electric
C219S508000, C374S110000
Reexamination Certificate
active
06173903
ABSTRACT:
This application claims priority under 35 U.S.C. § 119 to German patent application Serial No. 197 56 510.7, filed Dec. 19, 1997, which application is incorporated herein by specific reference.
BACKGROUND OF THE INVENTION
1. The Field of the Invention
This invention concerns systems and procedures for controlling the temperature of a material to be processed in the atmosphere of a processing chamber which is closed to the surrounding atmosphere, by comparing a desired temperature with the actual temperature in a first and a second control circuit. The actual temperatures are determined by at least two independent temperature sensors in the processing chamber. The temperatures undergo a plausibility test with a specified threshold difference value. Non-fulfillment of the plausibility condition causes a signal to be output and the energy supply for stabilizing the temperature of the processing chamber to be interrupted.
2. Present State of the Art
DE 31 00 273 A1 discloses a failure- and drift-proof temperature regulator in which two sensors determine the actual temperature in the processing chamber of an oven. A comparator then performs a plausibility check, according to which the difference between the two temperature signals must lie within a specified tolerance range for them to be plausible. As a prerequisite, it is assumed that it is extremely unlikely for an error of equal magnitude to occur in two temperature regulators or sensors simultaneously.
This reference also discloses the use of a logic system which tests at least two thermometers and which, if the temperature deviation is too great, not only outputs a warning signal but passes control of the temperature in a processing chamber from a first controller to a second controller. Here, the test characteristics are, e.g., the difference between the expected value and the actual value, the feed current of the instrument, the position of the limit switch in the instruments, and the duration of absence of a new command to change the control variable. Furthermore, the comparator can be blocked during a heating or cooling phase of the heat treatment system.
A temperature control device is also know from DE 82 29 723 U1 with a first thermostatic switch controlled by a first temperature-sensitive element, and a second thermostatic switch controlled by a second temperature-sensitive element. The second temperature-sensitive element can turn on the second thermostatic switch at a certain limit temperature outside the operating temperature range. The second thermostatic switch is arranged next to the first one and has a manual reset component. A display element arranged next thereto indicates its control state. Such a control device, when used on a freezer, is intended to display a warning if the normal control cycle within the operating temperature range has been disturbed, such as, e.g., during a longer power failure.
Here it turns out to be a problem that even when the plausibility condition of the temperature sensors is met, additional defects in the control circuit can occur. Such as, for example, false triggering of actuators. This, for example, can cause a contact to remain permanently closed.
An incubator is also know from DE 21 33 119 B2 which uses water as a circulating fluid and which uses temperature regulation to keep the water at a constant temperature level, such as 37° C., for example. It turns out to be a problem if an error occurs in the heating system. This makes it possible for the material in the useful space, for example cell cultures, to be endangered by overheating, for example. This also goes for falling below the specified temperatures when the heating completely fails. It is also possible for individual elements of the feedback control circuit to fail, for example, the temperature sensor. This can cause an uncontrolled situation which can destroy cell cultures.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
The task of the present invention is to protect the material being processed—especially cell cultures—against destruction by overheating or overcooling due to defects or component drift in feedback control circuit system. This can be caused by drift in temperature sensors or defective actuators. It should also make it possible to summon quick help from an operator if a system error should occur.
The task is solved, in the procedure according to the invention, by passing control from a first control circuit to a second control circuit when plausibility conditions are not met. The plausibility conditions are not met because the temperature rises above or falls below an adjustable tolerance band about a specified desired value (W
1
). The second control circuit includes a controller/monitoring device and an actuator.
It turns out to be advantageous if the complete control circuit, together with its sensor and actuator, is also monitored by a monitoring device. As a result, it is no longer possible for an error in the feedback control circuit or sensor system to destroy the material to be processed, for example a cell culture, by possible overheating or undercooling.
In a preferred embodiment of the procedure, the plausibility condition is evaluated as not being met if a specified difference between the two temperature sensor signals is exceeded. The difference can also be adjusted as a function of the difference between the desired value and the actual value or the absolute value.
If the plausibility condition is not met, the feedback controller/monitoring device outputs an actuating signal to stabilize the temperature of the atmosphere of the useful space. In practice this means that the monitoring device interrupts the supply of energy for stabilizing the temperature of the atmosphere of the useful space.
It has proved to be especially advantageous to determine the temperature of the useful space by two separate measuring systems. The two separate measuring systems include two discrete temperature sensors. The two temperatures from the sensors, that is the values of the signals from the sensors which measure the temperature, are cyclically compared with one another. It also turns out to be advantageous for sensor signal values falling outside the specified plausibility band of the selected measurement and feedback control range to trigger a permanent shutdown with an error message.
If the plausibility condition for two sensor signals S
1
and S
2
is met, and the desired value W
1
exceeds or falls below an adjustable tolerance band, the controller/monitoring device and the actuator which is connected therewith, takes over regulation as the primary feedback control circuit. If the measured temperature falls below the tolerance band and if the error time has run out, an error message is produced “Temperature below.” By contrast, if the temperature is above the tolerance band, an error message “Temperature above” is produced. Temperature regulation is then taken over by a “material protection” program in a controller/monitoring device with a connected main power cut-off relay which represents an actuator.
It has turned out to be especially advantageous that if the upper tolerance band value is exceeded, the procedure can further regulate the system to the desired temperature value W
1
which has been set via an all-pole main power cut-off relay.
The task is solved in a device to regulate the temperature of a material to be processed in a processing chamber with an atmosphere which can be closed off to the surroundings. The device includes at least a first and a second control circuit and each of their control inputs for an actual value signal being connected with a temperature sensor in the processing chamber. The first control circuit is connected with a first input of a comparison module and the second control circuit is connected with a second input of a comparison module. This is for the purpose of forming the difference between the actual temperature value signals and performing a plausibility test on the sensor signals. The plausibility test consists of whether the temperatures exceed a specified th
Heeg Hubert
Loscher Helmut
Kendro Laboratory Products GmbH
Wayner William
Workman & Nydegger & Seeley
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