GB728725A - Improvements relating to a liquid measuring machine - Google Patents

Abstract

A machine for measuring fractions of a body of liquid flowing from a chromatographic column comprises a series of receptacles 10, Fig. 2, which are successively brought beneath a nozzle 9 fed with separate constant volumes of liquid by a siphon device 1 (see Group XXIX). This device is provided with a funnel 4 placed beneath the chromatographic column and two electrodes 7 and 8 which are intermittently connected by the measured quantities passing through the device. The electrodes are arranged to connect the grid of a biased triode to its cathode and hence produce an increase of anode current which, through a relay, energizes a solenoid 19 arranged to rock a lever 17 carrying a spring-loaded pawl 16 and hence cause intermittent rotation of a rotary conveyer 11, so that each of the receptacles 10, which consist of glass tubes, is positioned in turn below the nozzle 9 to receive a single measured quantity of liquid. The lever 17 is restored to its original position by a spring 20 while a blade spring 24 prevents backward rotation of the conveyer. A second blade spring 23 engages the pawl 16 at the end of its feed stroke to prevent rotation of the conveyer due to its own inertia. Fig. 4 shows an alternative construction in which the conveyer 11 is provided with a spirally-arranged series of holes to receive the receptacles 10 and a similarly arranged series of bosses 37 to co-operate with a switch 70 secured to a pivotally-mounted arm 39 rigidly or resiliently connected to a guide pin 42 which traverses a spiral groove 43 parallel with the spiral line of the bosses 36. The switch 70 and the electrodes 7, 8 <PICT:0728725/III/1> <PICT:0728725/III/2> <PICT:0728725/III/3> form part of an electric control system for a moto 56, Fig. 5, which intermittently rotates the conveyer through a worm drive 34 and a friction disc 33. When the electrodes 7, 8 are closed by the passage of a measured quantity, a condenser 46 is connected in the grid circuit of a thyratron 44 to modify the phase relationship between the A.C. supplies to the grid and anode and hence energize a relay 48 provided with a holding circuit. This relay closes contacts 45, 55 to connect a condenser 49 across a rectifier 50 until the voltage on the condenser reaches a high enough value to energize a relay 64 which opens contacts 62, 63 to break the holding circuit of the relay 48, closes contacts 68, 69 to start the motor 56 and closes contacts 52, 65 to discharge the condenser 49 through a variable resistance 66. The switch 70, which is held open by one of the projections 37 while the conveyer is stationary, now closes while the contacts 68, 69 open as soon as the voltage on the condenser 49 has fallen sufficiently to de-energize the relay 64. The charging and discharging times for the condenser 49 are dependent on the values of resistors 54 and 66 and are preferably 10 and 4 seconds respectively, the former time corresponding to the period for which the conveyer is stationery. A counter 58 is included in the circuit. The bosses 37 may be replaced by a spiral line having a discontinuous property such as electrical conductivity, colour, state of surface or index of refraction. The last receptacle may consist of an overflow device.