GB2110382A

GB2110382A - Cleaning and calibrating environment monitoring sensor

Info

Publication number: GB2110382A
Application number: GB08233192A
Authority: GB
Inventors: Adrian Roger Parker
Original assignee: Partech Electronics Ltd
Current assignee: Partech Electronics Ltd
Priority date: 1981-11-21
Filing date: 1982-11-22
Publication date: 1983-06-15
Also published as: GB2110382B

Abstract

The sensor surface of an environmental monitoring instrument such as a dissolved oxygen or pH monitor has a sensor membrane surface (1) over which jets of air are blown periodically by tangentially arranged jets (6). A timer (9) which controls the air jets simultaneously controls a switch (10) which periodically calibrates the instrument with reference to the oxygen content of the air blown over the sensor surface. <IMAGE>

Description

SPECIFICATION Environmental monitoring instrument This invention relates to an environmental monitoring instrument, with particular, but not exclusive, reference to dissolved oxygen monitors and pH meters.

Instruments which have measuring heads or surfaces which are exposed to water, particularly sea water or river water, are prone to contamination and must be cleaned regularly if their accuracy and sensitivity are to be maintained.

The present invention provides a convenient means of maintaining the sensor surface of an underwater or other measuring instrument free of contamination. According to the invention there is provided a measuring instrument for environmental use having a sensor surface which is exposed to water in use, at least one air pipe terminating in an outlet arranged to direct a jet of air across the sensor surface, and means for controlling the application of air to the pipe or pipes to cause periodic cleaning of the sensor surface.

The means for controlling the application of air to the pipe or pipes may be under timer-control so that periodic cleaning of the sensor surface takes place automatically.

In the particular case of a dissolved oxygen monitor where the sensor surface is responsive to dissolved oxygen the means for controlling the periodic application of air to the pipe or pipes preferably also control switch means for effecting periodic calibration of the instrument. It is thereby arranged that each time air is blown across the sensor surface the instrument is calibrated by reference to the known, and substantially invariant, oxygen content of air.

In a preferred embodiment of the invention there are two or more said air pipes arranged to direct air jets across the sensor surface with a tangential component with reference to an imaginary circle centered on the sensor surface, so as to provide a vortex of cleaning air in the vicinity of the sensor surface.

Preferably the instrument is arranged in use with the sensor surface inclined to the vertical with a downwardly facing surface component so that air blown over the surface rises without accumulating on the surface. In this way the blown air carries away from the surface any contaminating material.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic perspective view of a dissolved oxygen monitoring instrument according to one embodiment of the invention, and Figure 2 is a diagrammatic transverse sectional view of the instrument shown in Figure 1, sectioned in the plane of the air pipes 5.

The instrument illustrated in the drawings is a dissolved oxygen monitor, in this case a galvanic probe oxygen analyser of the kind manufactured by Rexnord Instrument Products. This instrument has a lead anode and a platinum cathode forming an electrolytic cell, with an electrolyte of potassium iodide solution. The platinum cathode is separated from the test fluid, in this case water, by a thin membrane 1 of polytetrafluorethylene shielded from damage by a shroud 2 which is screwed onto one end of the casing 3 of the instrument. In use of the instrument the membrane 1 is immersed in the water or other fluid for which a reading of dissolved oxygen content is required. The output current from the instrument is proportional to the amount of oxygen gas diffusing into the electrolytic cell through the membrane 1.

To ensure that there is no stagnation of water in the vicinity of the surface of the membrane 1 the shroud 2 is provided with a number of apertures 4 through which water may flow.

To provide for the periodic cleaning of the exposed surface of the membrane 1 the instrument is further equipped with a number of air pipes 5 which terminate in outlets 6 arranged so as to direct jets of air across the surface of the membrane 1. In the illustrated embodiment there are three air pipes 5 (Figure 2) projecting through respective holes 4 in the shroud 2 and arranged so that their outlets 6 are tangential to a common imaginary circle C centered on the membrane 1.

The air pipes 5 are connected to a common air supply manifold 7 which is connected to a small compressor 8. The compressor 8 is controlled by a timer 9 which also controls a timer switch 10 connected to the electrical output of the instrument. The switch 10 normally directs the electrical output to a read-out circuit 11 which produces an electrical output in digital or analogue form. When the switch 10 is operated by the timer 9 the output of the instrument is taken to a correction and hold circuit 1 2 which measures the dissolved oxygen content of the air which, during the operation of the timer 9, is directed across the face of the membrane 1. This measured oxygen content is used as a calibration level and is memorised in the circuit 12 to provide a reference for the measurement of the dissolved oxygen content qf the water.Thus the correction and hold circuit 12 periodically re-calibrates the read-out circuit 11 each time the switch 10 is operated by the timer 9, Each operation of the timer 9 causes the compressor 8 to be energised and to direct air over the surface of the membrane 1. The tangential arrangement of the air jets produced by the air pipes 5 is such that the air swept over the surface of the membrane 1 forms a vortex, assisting the cleaning action and sweeping any debris away from the surface of the membrane 1.

The instrument is normally immersed in water with its axis inclined to the horizontal, so that the surface of the membrane 1 has a downwardly facing component. With this arrangement the air jets produced by each energisation of the compressor 8 form bubbles which rise through the holes 4 in the shroud 2, avoiding any accumulation of air on the surface of the membrane 1.

Although three air jets have been shown in the illustrated embodiment, it will be appreciated that in practice one or two jets may be employed, or more than three jets may be used, according to the nature of the instrument sensor surface to be cleaned.

The invention has been described with reference to the cleaning of sensor surfaces in dissolved oxygen monitoring equipment for underwater use. It will, however, be understood that the invention is generally applicable to the cleaning of glass surfaces or sensor surfaces in many other types of instrument, including optical sensors used for environmental measurements.

Claims

1. A measuring instrument for environmental use having a sensor surface which is exposed to the environment in use, at least one air supply pipe terminating adjacent said sensor surface in an outlet arranged to direct a jet of air across the sensor surface, and means for controlling the supply of air to said pipe or pipes to effect periodic cleaning of the sensor surface.

2. An instrument for the measurement of the dissolved oxygen content of water, said instrument having a dissolved oxygen sensor surface which is immersed in the water in use of the instrument, at least one air supply pipe terminating adjacent said sensor surface in an outlet arranged to direct a jet of air across the sensor surface, and means for controlling the periodic supply of air to said pipe or pipes to cause at least one cleaning jet of air to be directed across said surface, said control means including switch means operated upon each periodic supply of air to said pipe or pipes to effect calibration of the instrument with reference to the oxygen content of the air blown over the sensor surface.

3. An instrument as claimed in Claim 1 or Claim 2, in which there are at least two said air supply pipes arranged to direct air jets across the sensor surface, said air jets having directions which are tengential to a circle concentric with the centre of the sensor surface, whereby a vortex of cleaning air is produced in the vicinity of the sensor surface.

4. An instrument according to Claim 2, in which the sensor surface is inclined to the vertical and faces downwardly, whereby air blown over the surface rises without accumulating on said surface.

5. An instrument as claimed in Claim 2 or Claim 4, in which the sensor surface comprises a membrane and wherein said surface is surrounded by a shroud having apertures through which water flows over said surface.

6. An environmental monitoring instrument substantially as herein described with reference to and as shown in the accompanying drawings.