Measuring and testing – Liquid level or depth gauge – Immersible electrode type
Reexamination Certificate
1998-08-24
2001-06-26
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Immersible electrode type
Reexamination Certificate
active
06250153
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to sensors for sensing a medium within a container. More particular, this invention relates to non-metallic sensors for use in sensing certain conditions, such as medium level and temperature, of a corrosive medium, such as those encountered in the semiconductor industry in the processing of semiconductor wafers into circuit chips.
BACKGROUND OF THE INVENTION
In many industries it is important, and indeed even crucial, to monitor the conditions of a liquid within a housing or container. Monitoring of the liquid conditions is typically achieved using one or more gauges which extend into the housing and into contact with the liquid. However, in the semiconductor industry especially, and in other industries as well, extremely severe conditions are often times encountered within liquid containers due to the highly corrosive nature of many liquids.
Corrosive liquids are extremely hard on many gauges because metals which are used in conventional gauges cannot reliably withstand the corrosive environment for long periods of time. Thus, not only must conventional gauges be frequently replaced, thereby increasing costs, the processing equipment associated with the container must be shut down during gauge replacement, thereby affecting production and further increasing costs.
Conventional sensors are disclosed in U.S. Pat. Nos. 5,501,102 and 5,626,053 to Williamson. In these sensors, a pair of non-metallic, resistive/conductive members are provided in order to prevent corrosion by the corrosive environment within the container. The resistive/conductive members are formed from conductive, chopped carbon fibers embedded within a polymeric material. These sensors rely upon either a change in voltage or a change in current between the two members, which are in direct contact with the liquid, to provide an indication of the liquid level in the container. The resistive/conductive members, however, have a relatively high resistance, due to the chopped carbon fibers, which do not electrically align during formation of the members.
Another conventional sensor device is disclosed in U.S. Pat. No. 5,057,813 to Sasaki et al. This device is a digital output device for sensing whether a liquid, in this case oil, falls below a predetermined level. A metallic electrode is disposed inside of a sensor body, and the resistance between the sensor body and the electrode is detected to determine the oil level. This device, however, is not able to continuously sense the oil level. Further, due to the metallic nature of the electrode, this device would not be practical for use in highly corrosive environments.
U.S. Pat. No. 5,661,405 to Simon et al. discloses a sensor for us in electrically conductive liquids. The sensor uses two flexible ribbon electrodes surrounded by a pair of flexible sleeves. Each electrode is made from a carbon filled, silicon rubber material. Silicon rubber material offers very limited corrosion resistance and is therefore not suited for use in corrosive environments. Further, silicon is forbidden in the presence of silicone wafers during semiconductor manufacturing, and thus this sensor is not suitable for use in the semiconductor industry.
Therefore, there is a need for sensors that overcome the disadvantages of previous sensors. Further, there is a need for improved sensors for use in highly corrosive media, such as those used in the semiconductor industry, for sensing the conditions of the media.
SUMMARY OR THE INVENTION
The present invention provides improved sensors for use in sensing various conditions of a corrosive medium contained in a container. In particular, the sensors of the present invention can be used to sense the level and temperature of the corrosive medium in the container. The sensors have particular use in the semiconductor manufacturing industry, however the sensors have applications in the biotech, pharmaceutical, plating, chemical, petroleum, etc. industries as well. An advantage of the invention is that the conditions of the media can be continuously sensed, thereby providing an accurate indication of the media conditions at any point in time. Further, the sensors of the present invention are designed to reduce the chance of contamination of the media, as well as being designed with a reduced electrical resistance. Even further, the sensors of the present invention are simple in construction and use, and can be used to sense the level or temperature of liquid, gaseous, or solid media.
In one embodiment in accordance with the invention, a sensor for use within a container containing a medium is provided. The sensor comprises first and second elongate, conductive sensor members, each of which has a longitudinal axis and is dimensioned to extend into the medium. The first and second sensor members each include a core made from a non-metallic, electrically resistive material having a plurality of non-metallic conductive fibers embedded therein. Each core has opposite ends and the fibers are oriented parallel to the longitudinal axis of the first and second sensor members and extend continuously between the first and second ends of the cores.
In another embodiment in accordance with the present invention, a sensor member is provided comprising an elongate, conductive rod having a longitudinal axis. The rod includes a core made from a non-metallic, electrically resistive material having a plurality of non-metallic conductive fibers embedded therein. The core has opposite ends and the fibers are oriented parallel to the longitudinal axis of the rod and extend continuously between the ends of the core.
A variety of additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
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Collins Timothy R.
Henning Michael L.
Merchant & Gould P.C.
Sensor Measurement Technology
Williams Hezron
Worth Willie Morris
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