Monitoring device

#This invention relates to apparatus for monitoring fluids and in particular to a device for monitoring fluids by means of an indicator tape.

#It is known to monitor fluids, especially gas, and in particular to monitor toxic or noxious components of fluids, by causing a sample of the fluid to contact a tape impregnated with a substance which traps the fluid component to be monitored. Usually, but not necessarily, the substance which traps the fluid component will be an indicator which undergoes a colour change when exposed to the fluid component being monitored so that the tape becomes stained. Generally, a porous tape is employed, for example a paper-tape, and a sample of the fluid to be monitored is passed through the tape. Monitoring devices based on the above principle are known which comprise a pump for passing a fluid sample into contact with and/or through the tape and means for advancing the tape either continuously or intermittently to expose a fresh area of the tape to the fluid. An electric motor often is provided for driving the pump and a separate electric motor may be provided for driving the tape-advancement mechanism.

#A single power source, for example a battery, may be used to drive both motors.

#A preferred embodiment of the monitor, a personal instrument, is shown in the accompanying drawings, in which:

#FIG. 1 is a line diagram showing the inter-relationship of the component parts of the monitor,

#FIG. 2 is a section along the line A-A.sup.1 shown in FIG. 1, indicating the location of the tape between plates and fluid ports,

#Referring to FIGS. 1 and 2, a motor 1 and gearbox 2 are connected by a crank and connecting rod mechanism 3 to a reciprocating diaphragm pump 4. A speed reduction gearbox 5, connected directly to the crank mechanism 3, is connected to a tape-winding drum 7 via a clutch 6. The tape 9 is passed between a pair of plates 8 (which are resiliently biassed together, for example by springs, magnets or elastic bands not shown in the drawings) and attached to the winding drum 7. Each of the plates 8 is perforated with a single hole and the plates are brought together so that the holes are concentric as shown in detail in FIG. 2. The pump inlet is connected to the hole in one of the perforated plates by tube 10: the other perforated plate has a fluid inlet port 11 making contact with the hole therein. The fluid inlet port is adapted to make connection to a sampling chamber or to a drying tube or an absorption tube for pre-conversion of an undetectable substance into a detectable substance .

#When the motor 1 is powered it drives the crank mechanism 3 and pump 4 via the gearbox 2. At the same time the motor also drives the tape-winding drum 7 via the gearbox 5 and clutch 6 and so is able to move the tape 9 between the perforated plates 8. The pump 4 pulls the fluid sequentially through the inlet port 11, the first plate, the tape 9, the second plate and tube 10 before exhausting it from the pump outlet 12. The tape is made of porous paper chemically treated so that those components of the fluid it is desired to monitor, in passing through the tape, are trapped and give rise to a stain on the tape.

#The arrangement of the component parts fitted into a case of dimensions only 132 .times. 62 .times. 38 mm is shown in FIGS. 3 and 4. FIG. 3 is a side view showing the interior of the device with the side of the case removed and FIG. 4 is a view showing the internal layout with the upper plate of the case removed. The reference numerals are used in FIGS. 3 and 4 to denote the same component parts as those used in FIGS. 1 and 2. The monitor is particularly suited to use as a personal monitor for toxic gases which can be conveniently carried e.g. in a breast pocket or attached by a clip (see FIG. 3) to clothing when a person is working in, or is proposing to enter, a potentially toxic atmosphere.