Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-01-26
2001-06-26
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S406000, C204S415000, C204S432000, C204S401000
Reexamination Certificate
active
06251243
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to self-testing gas detecting apparatus.
BACKGROUND TO THE INVENTION
Electrochemical gas sensors typically comprise two or three electrodes separated by an electrolyte. These sensors generate currents in response to the presence of a gas, e.g. carbon monoxide hydrogen sulphide, sulphur dioxide, ammonia, for which they are adapted. Hitherto, faults in such sensors, for example broken signal wires or loss of electrolyte, have been detected by applying a quantity of the gas to be detected to a sensor while monitoring the sensor output. If a wire is broken or the electrolyte has leaked away, there will be no, or at least a reduced, output current.
The need to test such sensors by applying quantities of gas has a number of disadvantages. Staff are required to visit each sensor which is time consuming and undesirable if a sensor is located in a clean environment such as is found in semiconductor processing plants. Also, if a sensor fails, its failure will not be detected until the next test. This of course is undesirable where the sensor is used to detect a toxic gas or explosive. Furthermore, if the gas to be detected is toxic, it is undesirable that it be deliberately released during the testing process and for domestic use, in particular, this method of testing is quite unsuitable.
SUMMARY OF THE INVENTION
It is an aim of the present invention to overcome the aforementioned problems.
Broadly stated, the present invention provides a gas detecting apparatus including connection means for providing electrical connection to an electrochemical gas sensor, test means for generating a test signal and means to analyse a signal derived from the test signal to determine whether a serviceable electrochemical gas sensor is connected to the connection means.
A class of gas detecting apparatus to which the present invention is applicable comprise an amplifier and connection means for connecting an electrochemical gas sensor to the amplifier such that the amplifier is operable to amplify the output of the sensor.
According to a first aspect of the present invention, there is provided A self-testing gas detecting apparatus comprising an electrical interconnection for making a connection to an electrochemical gas sensor, a test signal generating circuit for generating a test signal, an amplifier for processing the test signal from the test signal generating circuit according to a transfer function, and a signalling device, said interconnection being arranged for connecting an electrochemical gas sensor as a component of the amplifier so as to determine said transfer function, wherein the signalling device is responsive to the processed test signal output by the amplifier to signal a fault condition if the processed test signal is not indicative of a serviceable electrochemical gas sensor being connnected into the amplifying circuit by said interconnection.
According to a second aspect of the present invention, there is provided a gas detecting apparatus comprising an electrical interconnection for receiving a two-terminal electrochemical gas sensor, a test signal generating circuit for generating a test signal, an amplifier for processing a test signal from the test signal generating circuit and processing means responsive to the processed test signal output by the amplifier to determine whether a serviceable electrochemical gas sensor is connected to the interconnection, the interconnection being arranged for connecting an electrochemical gas sensor to the amplifier such that the transfer function of the amplifier for the test signal is influenced thereby.
The interconnection preferably comprises a socket. However, the interconnection may comprise means to which a sensor may be conveniently soldered. The physical nature of the interconnection is not critical to the present invention, the key feature being the electrical relationship between the sensor and the amplifier. It should be noted that the test signal is not applied directly to the sensor and the result analysed. Instead, the presence of a serviceable sensor is determined indirectly from the output of the amplifier produced in response to the test signal.
Since, the transfer function of the amplifier for the test signal is influenced by the presence or absence of a serviceable electrochemical gas sensor, the output of the amplifier, in response to the test signal, will vary depending on the presence or absence of a serviceable gas sensor. The transfer function may be modified in respect of the amplifier's gain for the test signal or the phase shift introduced into the test signal by the amplifier. Preferably, however, the interconnection is configured such that the presence of a serviceable electrochemical cell increases the gain of the amplifier for said test signal.
If the test means is configured such that the test signal causes the amplifier to give a large output or saturate when a serviceable electrochemical sensor is connected to the amplifier by the interconnection, it is relatively simple to detect the presence of a sensor, for example using a digital or analogue comparator. A threshold for electrolyte loss can be set by testing the level of the amplifier output at a predetermined period after the start of the test signal. This is because the lower levels of electrolyte will result in the output of the amplifier being above the predetermined threshold for shorter periods.
Preferably, the amplifier is an operational amplifier, the interconnection is configured for connecting an electrochemical cell between the inverting input of the operational amplifier and earth, and the test means is configured to apply the test signal to the non-inverting input of the operational amplifier.
Conveniently, the test signal comprises a transient. The transient may be generated by means to produce a voltage step and differentiator for differentiating the voltage step to produce the test signal. The voltage step may be produced by a potential divider coupled between the amplifier's power supply lines. Thus, the sensor will be tested each time the amplifier is energised. However, a transient or ac signal may be applied at any time. Application of an ac signal at an appropriate frequency will result in the amplifier outputting a series of pulses.
In battery operated apparatus, power consumption is often reduced by intermittently operating circuits. Test signal generation linked to energising of the amplifier is particularly suited to such apparatus. Advantageously, therefore, apparatus according to the present invention includes control means and switching means for switching the supply of power to the amplifier and the test means, wherein the control means is operable to cyclically energise the amplifier and the test means.
REFERENCES:
patent: 3661748 (1972-05-01), Blackmer
patent: 3718568 (1973-02-01), Neuwelt
patent: 4088986 (1978-05-01), Boucher
patent: 4868508 (1989-09-01), Ohishi
patent: 5202637 (1993-04-01), Jones
patent: 636447 (1983-05-01), None
patent: 4318891 (1994-12-01), None
patent: 19510574 (1996-06-01), None
patent: 0039549 (1981-11-01), None
patent: 0241601 (1987-10-01), None
patent: 0508966 (1992-10-01), None
patent: 60-63473 (1985-04-01), None
patent: 1-44843 (1989-02-01), None
patent: 1-242958 (1989-09-01), None
patent: WO90/12315 (1990-10-01), None
Dilworth & Barrese
Tung T.
Zellweger Analytics Ltd.
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