The present invention relates to an electronic autoclave cycle sensor. Instruments used in surgery must be cleaned and sterilized after each use to eliminate microorganisms and viruses to prevent infection. While many sterilization methods are used, the most effective, lowest cost, quickest and most available method is application of steam in an autoclave. However, an autoclave provides a hostile environment causing wear on surgical instruments that, over time, requires maintenance to avoid instrument failure.
Often, manufacturers set prescribed design goals for their instruments including warranting the minimum number of autoclave cycles that the instrument is designed to withstand. Accordingly, it is helpful for the user to know how many autoclave cycles his or her instruments have undergone so that appropriate maintenance can be scheduled. Additionally, manufacturers of instruments are interested in knowing whether an instrument has been subjected to a sufficient number of autoclave cycles so as to render the instrument warranty void.
U.S. Pat. No. 3,450,489 to Fay discloses a sterilization control means that includes a thermal responsive signal producing means enclosed within wrapped articles to be sterilized. The signal means produces and transmits a control signal from within the bundle which is used to control the sterilization operation to ensure thorough sterilization of the wrapped articles. Fay fails to teach or suggest any means for counting the number of cycles to which an instrument has been subjected nor does Fay teach or suggest any magnetic means to sense the number of autoclave cycles to which an instrument has been subjected.
U.S. Pat. No. 3,568,627 to Sellenger et al. discloses a combined record card and sterilization indicator including a portion of the record that changes colors to indicate that sterilization has taken place. Sellenger et al. fail to teach or suggest any magnetic means for counting the number of autoclave cycles to which an instrument has been subjected.
U.S. Pat. No. 4,235,842 to Thomas et al. discloses a temperature cycle indicating means for a sterilizer unit that is designed to count the number of cycles of sterilization to which contact lenses have been subjected. Thomas et al. fail to teach or suggest the use of magnetic means to perform such function.
The present invention relates to an electronic autoclave cycle sensor. The invention records the number of thermal cycles to which an instrument has been subjected in a steam autoclave. Since surgical instruments are not supplied with power during autoclave sterilization, the inventive sensor is required to record the existence of a temperature change cycle passively, which event must be detectable through electrical reading and wherein the sensor must be electrically re-settable.
When a sterilization cycle has been completed, and the instrument is next energized in use, computer means comprising a microprocessor or microcontroller is employed to read the sensor and record the occurrence of a sterilization cycle.
Information as to the cumulative number of cycles through which the instrument has been subjected is stored in a nonvolatile memory means such as, for example, an EEPROM. This data is suitably displayed on a display panel and/or is read out to a service computer on a serial data port or over a modem to a factory service center.
When an unmagnetized ferromagnetic material is placed in a magnetic field, such as is the case when a current passes through a coil around the material, the flux density of the material rises. When the magnetic field is removed by stopping flow of the current, the flux density remains. This phenomenon is known as 'permanent magnetism'. If the temperature of the material is raised above a critical value called the 'Curie temperature', the exchange coupling
suddenly disappears and the material becomes simply 'paramagnetic'. Paramagnetic materials do not exhibit the properties of permanent magnetism and their flux density is zero in the absence of an external field. At temperatures near but below the Curie temperature, the effect is only partial causing a permanent magnet to lose some of its retained flux density.
In the present invention, the sensor means employed uses either the Curie temperature or a temperature near but below the Curie temperature of a ferromagnetic material by first magnetizing the material and then, later, checking its flux density to determine whether a thermal cycle has occurred. As should be understood from the above explanation, if the magnetized material has been exposed to a temperature at or near the Curie temperature, the magnetic flux density will fall and this fact can be sensed through energization of a magnetic sensor. After sensing and recordation of an autoclave sterilization cycle, the magnetic material is re-magnetized so that it is ready to be used to sense the next sterilization cycle.
In the preferred embodiment, the magnetic material employed has a relatively low Curie temperature so that its Curie temperature is reached or approached within the normal range of operating temperatures of an autoclave. An example of such a material is Nd--Fe--B alloy.
The present invention contemplates two possible sensor means for measuring the flux density of a magnetizable material. In a first embodiment, a Hall effect sensor is used to directly measure the magnetic field strength of the magnetizable material so that the user can determine whether the magnetic field strength has been reduced as would be the case should the material be exposed to the near Curie or Curie temperature thereof. In a second embodiment, a sensor winding is used to sense the magnetic field strength of the magnetizable material which can be made in a variety of shapes such as toroid shaped, similar to that used in magnetic core memory devices. The sensor winding is interconnected with an amplifier so that changes in flux can be sensed.
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