Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus expansion or extension
Reexamination Certificate
2000-04-19
2002-08-27
Wong, Peter (Department: 2181)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus expansion or extension
C710S305000, C250S345000
Reexamination Certificate
active
06442639
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a docking station for an environmental monitoring instrument and the interaction between the docking station, the instrument and a service center.
2. Description of Related Art
Potentially dangerous gas mixtures (e.g. combustible gases, toxic gases, excessively high or low oxygen concentrations), noise levels, particulates etc. are found in many work place environments. These dangers are well known and monitoring instruments are available to detect a wide range of potential hazards. Monitoring instruments are also available for other applications including environmental monitoring, such as water quality (e.g. pH, dissolved oxygen, suspended solids, dissolved ions, clarity), pollution control (e.g. volatile organic compounds VOC's, oxides of nitrogen, ozone, particulates etc.), indoor air quality (e.g. carbon dioxide, relative humidity, temperature), and quality of compressed air for a breathing apparatus (e.g. oxygen, carbon monoxide, carbon dioxide, relative humidity). These monitoring instruments typically contain one or more sensors, a signal processing means and output.
For many monitoring applications, if the concentration of the analyte or the magnitude of a physical parameter determined exceeds pre-determined limits, then the instrument may provide an alarm to warn nearby personnel, or it may activate other remedial actions. For example, the instrument may initiate actions such as increasing ventilation or diverting a drinking water stream if the water quality levels are outside of the allowed limits, until the problem is corrected.
Monitoring instruments for safety and environmental applications are broadly divided into two groups, portable instruments which are designed to be hand held or worn by the user, or can easily be transported from one location to another, and fixed instruments which are typically mounted in a fixed location and which provide monitoring at that location.
Monitoring instruments typically contain one or more sensors, which provide an electrical response that varies with the concentration of the analyte or with a parameter being measured. For each sensor, there is associated circuitry for driving the sensor, for measuring and displaying and/or recording the output and for activating visual, vibrational or audible alarms used to notify the user of the presence of a potentially hazardous condition.
Most instruments also contain a microprocessor or other controller and memory features that allow for more complex data analysis, such as industrial hygiene functions. Examples of industrial hygiene functions include calculating time weighted exposure limits, or recording the variation in exposure over time for later analysis. For many toxic substances, especially gases, the time-weighted exposure is as important as the short-term exposure concentration. For example, carbon monoxide has an Immediately Dangerous to Life and Health (IDLH) concentration of 1200 ppm; this corresponds to the maximum concentration of gas from which the average worker can escape without a respirator and without loss of life or irreversible health effects in less than thirty minutes. However, the time weighted average permissible exposure limit (TWA-PEL) to carbon monoxide is only 50 ppm (OSHA); this is the maximum exposure that the average worker can be exposed to for eight hours a day, forty hours a week, repetitively, without adverse effects (NIOSH Pocket Guide to Chemical Hazards, US Department of Health and Human Services, June 1997). Typically, an analytical instrument will store the exposure data for at least one eight-hour shift, and then the data is downloaded to a computer for record keeping and further analysis.
In locations where high concentrations of toxic gases or low concentrations of oxygen are expected, workers may be supplied with a breathable air supply from a compressed gas source. Usually these air supplies incorporate instruments which monitor for toxic and other gases (e.g. carbon monoxide), since if this air supply is contaminated (e.g. by malfunction of the compressor), then it could be very detrimental to the workers who depend on it.
In typical use, a monitoring instrument is calibrated prior to use, a laborious process. Using hazardous gas monitoring as an example, the sensor background outputs are initially set to zero for both toxic and combustible gases by exposure of the instrument to clean air or zero gas. Subsequently, the instrument is exposed to a test mixture, which contains one or more active components of known concentration to which the sensors respond. For calibrating gas sensors, the test mixture is a known concentration of the analyte gas in inert balance gas. For a pH measuring electrode, the calibration may be performed using one or more buffer solutions of known pH as the test mixture. Similarly, other types of sensors will require their own specific test mixtures for calibration. The output of the instrument being calibrated is then set to the known value of the test mixture for each sensor.
The calibration process will vary with each type of sensor and instrument, but all processes involve matching the output of the instrument to a known value, usually a test mixture. For most applications involving safety and environmental monitoring, detailed records of the calibration results are required. The calibration interval depends on the sensor type, the instrument design and on the specific environment in which the instrument is being used. Typically, electrochemical and catalytic gas sensors are calibrated monthly whereas infrared-based gas sensors are calibrated annually. However, there is considerable variation between manufacturers and even instrument models that use similar sensor technology.
Though most sensor technologies are very reliable, as required for safety and environmental applications, sensors do sometimes fail in service. Some sensors, such as galvanic oxygen sensors, are consumed during the oxygen detection reaction and so have a limited lifetime. Many sensors do not have a fixed service life and only fail when a problem develops or the sensor is damaged (e.g. contamination of a pH electrode).
Whereas calibration is usually only performed at fixed time intervals, for many safety and environmental applications it is common practice to “bump test” monitoring instruments to ensure that they are working correctly. The bump test typically involves application of a test mixture to the instrument for enough time to active the warming alarms or other modes of display that indicate that the instrument responded correctly. While the bump test procedure takes less time than a full calibration, it still requires the expense of both time and obtaining a test mixture of known composition.
One area of current development is in-situ diagnostic testing. These tests are performed automatically by the instrument, either with, or preferably without human intervention. Diagnostic methods have been developed for a variety of different sensor types. For example, electrode capacitance methods have been described by Jones in U.S. Pat. No. 5,202,637 and by Studer in U.S. Pat. No. 5,611,909 for electrochemical toxic gases sensors. Parker described a method for galvanic oxygen sensors in U.S. Pat. No. 5,405,512 and Wang et al described a diagnostic method for polarographic oxygen sensors in U.S. Pat. No. 5,558,752. A method for identifying a failing combustible gas sensor has been described by Tantram in U.S. Pat. No. 3,960,495. These diagnostic tests provide the means for evaluating whether critical instrument components, such as the gas sensors are working correctly. Ideally, the instrument, without human involvement, can perform these tests periodically and automatically, and if a component fails the test, then the user is alerted to the problem.
These diagnostic tests have many advantages, such as low cost and automatic operation without human intervention; however in most cases, the best method for testing a sensor is with the intended analyte. For
McElhattan Kent D.
Skourlis James
Wagner David D.
Wang Annie Q.
Dennison, Schultz & Dougherty
Industrial Scientific Corporation
Vo Tim
Wong Peter
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