Electricity: measuring and testing – Electrolyte properties
Patent
1991-09-25
1993-04-13
Harvey, Jack B.
Electricity: measuring and testing
Electrolyte properties
204401, 324 711, G01N 2700
Patent
active
052026370
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a gas monitor incorporating one or more amperometric gas sensors and in particular it relates to improvements in the electronic circuits of the monitors allowing the monitor to test that the sensor is working properly.
BACKGROUND ART
Gas monitors are known that include one or more replaceable amperometric gas sensors providing an electrical current the magnitude of which provides a measure of the amount of gas detected in an atmosphere. This signal is analysed by circuitry within the monitor to give a monitor output which may be in the form of a display (in an analogue or digital form) of the amount of a specific gas detected and/or the output may be a printer or plotter and/or an alarm to give an audible and/or visual warning if the concentration of a gas falls to an undesirable level or if the concentration of a gas arises above a certain threshold level; the output signal could be recorded for subsequent analysis. However, the gas monitor need not necessarily give a direct indication of the amount of gas detected but may use the signal from one or more sensors to compute another parameter which may be displayed or printed; thus, the signal from a gas sensor may be used, together with other measurements, to compute the efficiency of a boiler (see British Patent No. 2,064,780).
The sensors used in the monitors of the present invention are amperometric electrochemical sensors of the type having a sensing (or working) electrode which is in communication with the atmosphere being sensed, a counter electrode and a reference electrode and all three electrodes are in contact with electrolyte within the sensor and are connected via respective terminals to the circuitry within the monitor; sensors of this type will be eferred to herein as "three electrode sensors". The potential difference between the sensing electrode and the reference electrode may be controlled and in some sensors this is done by connecting these two electrodes to the inputs of an operational amplifier either directly or through a resistor, e.g. see British Patent Specification Nos. 1,101,101 and 1,385,201 and U.S. Pat. No. 3,776,832 and European Patent Application No. 0,220,896A.
A circuit generally in accordance with the above patents is set out in FIG. 1 of the accompanying drawings. In FIG. 1, the sensor is indicated by the general reference number 10 and includes an electrolyte (sulphuric acid), a sensing electrode 12, a reference electrode 14 and a counter electrode 16 all of which are in contact with the electrolyte. The sensing electrode and the reference electrode are joined via terminals 12a and 14a to respective inputs of an operational amplifier 18 whose output is connected to the counter electrode 16 via terminal 16a. A resistor 20 is present between the sensing electrode 12 and its input to the operational amplifier 18. The sensing electrode 12 is in contact with an atmosphere that is being monitored and when the atmosphere contains a gas of the type being detected, this gas undergoes an electrochemical reaction which depolarizes the sensing electrode 12 causing the potential of that electrode to alter and so cause an imbalance between the potential of the sensing electrode 12 and the reference electrode 14 and hence between the inputs of the operational amplifier 18. The potential difference between the operational amplifier inputs causes the operational amplifier to supply current through its output to counter electrode 16 and hence causes a current to flow in the sensor cell 10 between the counter electrode 16 and the sensing electrode 12 (however substantially no current flows between the reference electrode and the sensing electrode). The current flowing through the sensor cell, which is directly related to the amount of gas in the atmosphere, can be measured, for example, by including a resistor between the amplifier output and the counter electrode 16 and measuring the voltage drop across the resistor (see U.S. Pat. No. 3,776,832); alternatively, the current flowing thro
REFERENCES:
patent: 3661748 (1972-05-01), Blackmer
patent: 3718568 (1973-02-01), Neuwelt
patent: 3776832 (1973-12-01), Oswin et al.
patent: 4443763 (1984-04-01), Marsoner
patent: 4900422 (1990-02-01), Bryan et al.
patent: 4956063 (1990-09-01), Hale
patent: 4985123 (1991-01-01), Curley
patent: 5016201 (1991-05-01), Bryan et al.
Harvey Jack B.
Neotronics Limited
Regan Maura K.
LandOfFree
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