Patent GB-1330291-A (GB)
Title: Measurement recording systems
IPC: G01D15/24
Filed: 1969-09-30
Abstract: 1330291 Recording-apparatus PYE Ltd 21 Dec 1970 [30 Sept 1969 15 Dec 1970] 47998/69 Heading G1J A method of synchronizing the operation of a chart recorder and a scanning measurement apparatus which are mechanically independent of one another includes the steps of (a) causing scanning means to reset in the scanning direction to a starting condition corresponding to a first predetermined value (210 nm) of a first variable (wavelength), (b) causing recording displacement means to drive forward in the recording direction to a corresponding starting condition in which a datum position representing the first predetermined value on the chart registers with marking means and (c) causing the scanning means and recording displacement means to begin a measurement recording scan simultaneously from the starting conditions in response to both conditions having been attained. In a scanning spectrophotometer the wavelength of radiation incident on a detector can be varied at a uniform rate by rotating a diffraction grating or prism by means of a cam follower bearing on a suitably shaped cam 3 driven at a uniform rate by a motor 2. The cam shaft 1 carries a drum 4 supporting a wavelength scale 5 with transparent graduations having some principal graduations extending above the drum 4 to provide signals to a control unit 9 (through an amplifier 8) when passing between a lamp 6 and photo-cell 7. A graduated strip chart has sprocket holes coinciding with major graduation marks on the chart and engaging sprocket wheels 12, 13 whereby the chart can be driven by a motor 11. A pen can be moved over the chart in a transverse direction in accordance with the output of the radiation detector. The sprocket 13 has holes 17 spaced in correspondence with the major graduation marks along the chart to provide signals to the control unit 9 (through an amplifier 16) when passing between a lamp 14 and photocell 15, positioned so that the signal occurs when a major graduation mark registers with the pen. The speeds of the motors 2 and 11 can be synchronized by supplying them from a common source of pulses and, through the logic circuitry provided in the control unit 9 for a first embodiment, a wavelength value of say 210nm at the bottom of a range to be scanned can be made to correspond with a major graduation mark on the chart by actuating a start switch 18 (i) to cause the motor 2 to drive the drum 4 quickly in reverse until a pin 19 actuates a switch 20 at a position corresponding to 200nm which (ii) causes the motor 2 to drive the drum 4 forward until the principal graduation for 210nm allows the photocell 7 to feed a pulse to the unit 9 which (iii) causes the motor 2 to stop and (iv) the motor 11 to drive the chart until a hole 17 in sprocket 13 allows the photo-cell 15 to feed a pulse to the unit 9 which causes (v) the motor 2 to drive the scanner forward so that scanning and recording proceed in synchronism from 210nm until, at say 410nm, a limit switch 22 stops motors 2 and 11, after which a further recording scan can be effected by re-actuating switch 18. In other embodiments the logic circuitry provided in the control unit 9 is arranged to produce the required result by different sequences of steps which may also include (vi) stopping motor 11 (at 210nm) (vii) starting motor 11 (at 210nm) the several embodiments I, II, III and IV comprising the following sequences: - I i ii iii+iv v II i iii+iv ii+vi vii III iv i+vi ii vii IV i ii+iv "d" v+vii where "d" represents a delay which may be omitted. In order to supervise several scans the switch 22 can be arranged to reverse the chart drive, lift the pen and interrupt signals to pen traversing means. A limit switch 30 is actuated when the major graduation mark representing the start of the scan has passed the pen and causes the motor 11 to stop. The switch 30 can be replaced by a reversible counter adding and subtracting pulses from the photo-cell 15 during forward and reverse chart drive respectively. Other reversible counters fed by the photo-cell 7 could be provided in the unit 9 to replace limit switches 20, 22. In alternative embodiments (a) the shaft 1 may rotate continuously, the cam 3 being shaped to return the wavelength setting, (b) signals signifying the end of a scan can be used to alter a third parameter or to change samples in succession and (c) the invention may be applied to scanning measuring instruments other than spectrophotometers for example mass spectrometers.