Patent GB-998475-A (GB)
Title: Gas analysis
Inventor: BECKER EARL MATHEW
IPC: G01N30/88
Filed: 1961-08-03
Abstract: 998,475. Gas analysis. MINE SAFETY APPLIANCES CO. Aug. 3, 1961, No. 28290/61 Heading B1L. A sample of gas is analysed by first passing it, together with a carrier gas, through at least one chromatographic column 65, 66, Fig. 6, to effect separation of its constituents, under control of valves 61, 62 which are themselves controlled to operate in a predetermined sequence by means of a marked continuous tape or film 21 (Fig. 4). Such control is also applicable to the gas-liquid partition type of fluid chromatography. Marks 32 are made in pencil on tape 21, which is passed between a lamp and photo-cell, Fig. 3 (not shown), whereby each mark 32 causes a four-level, stepping relay 34 to advance one step (Fig. 1). Level 34A ensures synchronization, whereby as long mark 27, Fig. 4, passes the photo-cell, a thermal relay, Fig. 2 (not shown), is able to respond causing relay 34 to actuate repeatedly unless or until it is in its number one position. Positions one to four of levels 34C, 34D, Fig. 7 (not shown), control power supply to either of windings 157, 158 of a motor 50, Fig. 5, which thereby, through Geneva mechanism 60, turns valves 61, 62 in a predetermined sequence of four movements at time intervals determined by the spacing of marks 32 on tape 21. Two chromatographic columns 65, 66 may be used in turn, in parallel or in series as shown, Fig. 6. Initially carrier gas, helium, flows from 81 through A, F, column 65, M, N, I, J, column 66, K, L, to outlet 81A. Sample gas flows from 83 to 83A via G, C, B, E, D, H. At step one of relay 34, valve 61 turns 90 degrees clockwise, and the carrier gas then carries sample gas which is trapped in conduits C, B, E, D, into columns 65, 66. At step two valve 61 turns 90 degrees anticlockwise, and at step three valve 62 turns 90 degrees anticlockwise. At this position column 66, which by now contains all the light components of the sample, is shortcircuited, while the heavy components now eluting from column 65 are carried out at 81A. At step four valve 62 turns 90 degrees clockwise, restoring column 66 to circuit and the light components in turn are carried to 81A. The various components of the gas sample originally trapped in C, B, E, D emerge at 81A separated out into bands. From 81A, the gases enter a detector 24, Figs. 1 and 8, which comprises a thermal conductivity cell and identifies each gas and gives a signal indicating its nature and quantity. This signal passes to a recorder 40, Fig. 1, via an attenuator 38. Attenuator 38 is controlled by steps five to twenty-four of level 34D, according to predetermined settings, so as to attenuate the signals to bring them within the range of recorder 40. Level 34B controls recorder chart movement. The detector cell 24, valves 61, 62 and their Geneva mechanism 60, and columns 65, 66 are all enclosed in a Dewar flask 86, Fig. 8, columns 65, 66 being of metal tube, wrapped round a massive aluminium mandrel 90. Bimetal thermostats 95, 96 and heater 92, which is operated at one of two powers or switched off by a control circuit, Fig. 9 (not shown), accurately maintain the temperature in flask 86 (at about 500 ‹F.). Flask 86 is surrounded by a zone 120 of lower but controlled temperature having a heater 99 and air circulator 98. Position twenty-six of level 34D powers servo 42 to adjust the zero of detector 24, a manual knob 45, Fig. 1, serving the same purpose. Button 46, Fig. 2 (not shown), may be used instead of the tape 21 and, when pressed, produces the same effect as a mark 32 on the tape.