Measuring and testing – Instrument casing
Reexamination Certificate
2001-09-08
2003-11-18
Williams, Hezron (Department: 2856)
Measuring and testing
Instrument casing
C422S098000
Reexamination Certificate
active
06647783
ABSTRACT:
BACKGROUND OF THE INVENTION
In many industries and situations, it is necessary to sample the atmosphere in a defined area. The sampling is used to monitor environmental conditions and can be conducted periodically or continuously.
One common application of such monitoring is to sample the atmosphere for levels of certain gases. Leak detection is a prime example. Leak detection is often used in refrigeration systems, air conditioning systems, systems where carbon monoxide or other harmful gases may be present, and the like. The chemical industry and the food storage industry are examples of industries that use such monitoring systems. Gases that are often monitored include NH
3
, CO
2
, H
2
, Cl
2
, CFCs, HCFCs, HFCs, CH
4
, O
2
and the like. Upon sensing a predetermined condition, such monitoring systems generate signals indicating gas concentrations above prescribed limits. The typical system responses include triggering alarms, summoning help and controlling (e.g., shutting down) equipment, etc.
Various sensor technologies measure selected PPM (parts per million) setpoints from OSHA's Permissible Exposure Limit (PEL) and the Threshold Value Limit/Short-Term Exposure Limit (TVL-STEL) up to the Lower Explosive Limit (LEL) range and indicate concentration levels with bargraph displays. Field-adjustable setpoints allow an operator to set or adjust warning and alarm trip levels at a main control panel.
One specific gas monitoring system manufactured and sold by Manning Systems, Inc. of Lenexa, Kans., identified by the name GM-10, includes three types of visual status indications for each of a plurality of channels. A warning LED indicates that the operator-selected warning setpoint has been exceeded, and the system includes elements to trigger a common warning relay and an individual warning relay for that channel on an optional relay board. The alarm LED operates in a similar manner for the alarm level, but also triggers a common horn relay and a buzzer relay which can be cleared manually. A fault on any channel triggers a common fault and horn relays and the buzzer. When any channel goes into a specified trip condition by sensing element levels beyond a setpoint, common relays for Warning, Alarm, Fault and/or auxiliary Horn are activated. An optional plug-in communication port for Ethernet or MOD-BUS connection provides remote monitoring of the system status/alarm functions. The GM-10 monitor uses diffusion for gas detection and provides continuous monitoring of a wide range of areas. Several areas can be monitored simultaneously. The GM-10 monitor can interface to, but can operate independently of, plant control systems.
Manning Systems, Inc. also manufactures and sells a sensor under the name EC which comprises a pair of polarized electrodes isolated from ambient air by a gas permeable membrane. As gas diffuses into a sensor, a redox reaction occurs generating a current linearly proportional to gas concentration. Readouts of the model EC have built-in visual and audible alarms, as well as relay output for ventilation fan activation, central alarm tie-in and the like. In addition, the EC model can provide direct input into PLCs and computer control systems.
As used herein, the term “fluid” includes gas as well as liquid.
Many sensors used in monitoring systems are sensitive to temperature, humidity, contamination or other such environmental conditions. If the environmental conditions are not within a certain specified range, the readings of the sensors associated with the monitoring system can be slow or suspect. Extreme environmental conditions can also deteriorate sensor performance and ultimately contribute to the sensor failure.
Therefore, there is a need for a monitoring system which can maintain the environment around a sensor within a specified range.
For example, if a monitoring system is used in a refrigeration system, conditions adjacent to the sensor may create a humidity condition that is out of the specified range for accurate and reliable operation of the monitoring system. Furthermore, a cycle of freezing and warming may degrade certain elements of the monitoring system, especially when combined with a high humidity environment. Condenser coils in refrigerated facilities also tend to contribute to high moisture levels. For example, when the coils are defrosted significant amounts of moisture are obtained therefrom, which often refreezes and coats the walls, ceilings, etc. of large, commercial freezers. Such ice coatings can significantly compromise the performance of prior art sensors, particularly those with externally-mounted sensor elements which are susceptible to ice coating because they are exposed. Gas sensing problems are also encountered when the temperature around the sensor element is at or near the dew point, whereby reliable readings are difficult to obtain.
Therefore, there is a need for a monitoring system that can ensure that the humidity and temperature in the vicinity of humidity and/or temperature sensitive instruments of the monitoring system are maintained within specified ranges.
Still further, some monitoring systems may be located in areas that are periodically washed, as by applying high pressure washing fluid to the area. The washing fluid from the washing process may lodge on or near the sensor or other equipment of the monitoring system and can create an undesirable condition which may adversely affect the readings of the system.
Therefore, it is desirable to efficiently remove any fluid used to clean a monitored area from the environment adjacent to a sensor and its associated equipment of a monitoring system.
Therefore, there is a need for a monitoring system from which fluid may be efficiently removed.
Previous monitoring systems included fluid-tight sealed housings or enclosures. These were intended to protect certain sensor components, such as the electronics, microprocessors, etc. from the adverse effects of exposure to harsh ambient conditions within the extreme environments being monitored. Monitoring was accomplished by mounting the sensor element externally. The enclosure structures for housing the electronics and other protected components were typically impervious materials such as metal or plastic, with fluid-tight seals and/or gaskets providing the necessary sealing for covers and access panels. Standards promulgated by the National Electrical Manufacturers Association (NEMA) provided ratings for different levels of airtight security, with NEMA Class 4 being the highest. NEMA Class 4 enclosures were often specified for extreme environments. However, this configuration of enclosures has several disadvantages. For example, even the tightest enclosure is susceptible to trace amounts of air infiltration, whereby moisture and other degrading elements can accumulate in the housing interiors. Moreover, the seals and gaskets are subject to deterioration over time, thus further compromising the operation of the sensors and contributing to false readings, etc. Still further, the externally-mounted sensor elements are susceptible to moisture-related degradation with corresponding performance degradation.
Therefore, there is a need for a monitoring system in which proper environmental conditions adjacent to the sensor and other equipment can be maintained without being subject to or vitiated by improper sealing or closure of a housing of the monitoring system. Preferably NEMA Class 1 enclosures can be utilized for cost effectiveness.
Furthermore, temperature and humidity conditions may cause condensation to form in the monitoring system, even in an air-tight housing. Such condensation may create problems for the sensor or its associated elements or the readings of the monitoring system. Accumulated condensation can turn to ice or frost in certain conditions. Ice or frost may adversely affect the operation and/or reliability of the monitoring system, including the sensor and its related circuitry. At best, the elements of the monitoring system will have to be designed to account for the presence of ice and/or frost, which may
EuDaly Brian K.
Wewers Frank J.
Manning Systems Inc.
P J Z
Shughart Thomson & Kilroy P.C.
Williams Hezron
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