Patent GB-745643-A (GB)
Title: Improvements in or relating to electrical recording systems
Inventor: CARLISLE SAMUEL SKIPTON
IPC: G01R13/04
Filed: 1952-08-21
Abstract: 745,643. Voltage measuring systems. BRITISH IRON & STEEL RESEARCH ASSOCIATION. Nov. 11, 1953 [Aug. 21, 1952], No. 21017/52. Class 37. [Also in Group XIX] The invention provides a multi-point measuring system in which the voltage prevailing at each of the points is compared in turn with a scan or reference voltage and uses (i) a recorder comprising a helical marking member and (ii) bias voltages different for each point and affecting the scan voltage to produce side-by-side recording on a single recording medium. In the embodiment described single point working may be used, if desired. Also the biasing in multi-point working resistor chain providing the bias voltages may be de-energized to permit overlapping presentation of voltage values (for greater reading accuracy). General description.-In Fig. 1 a saw-tooth scan voltage is generated by a linear sweep potentiometer 10 rotating in synchronism with drum 18 carrying a single turn wire helix electrode 19 above electrolytic recording paper or chart 22 and writing bar electrode 23. The output of sweep potentiometer 10 is continuously in series with any selected one of the plural D.C. input voltages 11 (only one shown) and the difference voltage is modulated into square waves by high-speed (e.g. 300 c/s.) chopper relay 14. When the scan voltage 10 equals the voltage 11 the square waves reverse in phase and a phase-sensitive amplifier/rectifier 16 fed from relay 14 and transformer 15 then delivers peak output (see details below) and triggers a pulse generator 17 to produce a voltage pulse at 24 and this is applied across electrodes 19, 23 so that chart 22 is marked at that point across its width which is nearest to helix electrode 19 when the voltage pulse occurs. The position of the mark on chart 22 represents the magnitude of the selected voltage 11. The scan voltage 10 is biased differently and automatically as each voltage 11 is selected (see below) so that in effect the scan is shifted relative to the rotation of the helix electrode 19 and the reference point for each input voltage 11 is at a different position on the chart 22. The biasing may be adjusted according to the number of input voltages to be recorded so that the reference points are always equally spaced. Circuit details: Phase-sensitive amplifier/ rectifier (16) and pulse generator (17) (see Fig. 2).-The output of transformer 15 goes through push-pull amplifier stages 30-31/. 32-33 into phase-sensitive rectifier 34-35 The suppressor grids of pentodes 34-35 are fed with square waves at 36 from the oscillator energizing chopper relay 14. As the scan voltage 10 sweeps through equality with selected voltage 11 the output from pentodes 34-35 swings through the trigger range of Schmitt trigger 38-39. The latter changes over and gives a step voltage output at the instant of in-phase of the voltages applied to the control and suppressor grids 34-35 and thus coincidence of scan 10 and input 11 voltages. This step voltage is differentiated at 40 and the ensuing short-duration pulse triggers squarewave generator 41, 42 which feeds via cathode follower 43 and terminals 24 the recorder electrodes 19, 23. Selection and bias arrangements and recorder control circuits (Figs. 3-4).-A standard 25- way uniselector 50 is used with contacts 1-13, 2-14, &c. connected together for a maximum of 12-point working from input voltage (11) terminals 1-12 at 57 and the required bias for each input 57 is taken from a resistor chain 61. A potentiometer 62 across each resistor 61 permits adjustment of each recording channel by a small amount. With 12-point working assumed as in the Fig. 3 set-up then as the recorder drum 18 completes one revolution slider 25 becomes momentarily free from contact with potentiometer 10 and rotating cam 54 closes switch 53 to operate stepping magnet 51 so that all the wipers of uniselector 50 advance one step. If this step is on to contact 25 then wiper 56 on bank 55 again energizes magnet 51 and all wipers proceed to contact 1 and under this condition the whole of chain 61 biases the scan voltage 10, whereby the correct portion of chart 22 is marked with the voltage prevailing at point or location No. 1. When the voltage at point No. 12 has been recorded the chart 22 is fed forward one step by wiper 69 on bank 68 energizing magnet/ratchet 67. A time scale is provided by means including cams 71-72 and relays 73-75. Cam 72 operates a switch 76 once every 10 minutes (say) and cam 71 closes switch 77 once per revolution of drum 18 so that directly 77 closes following closure of 76 the relay 73 operates and relay 74 holds, whereby pulse output 24 is disconnected and helix electrode 19 tied to D.C. at 79 through relay contact 74c and switch 80 for precisely one revolution of drum 18, therefore draws a line across chart 22. The holding of relay 74 is accomplished by relay 75 and when 77 next closes 74 is de-energized and maintained thus when 77 opens. The apparatus may be used for recording information relating to laboratory &c. processes and in this connection when samples are taken for analysis or substances are added in the process the exact time of such an occurrence is given on the chart 22 by pushbutton change-over of switch 80 to short switch 76 so that relays 73-75 and switch 77 operate to connect up electrode 19 to 50 c/s. source at 83 and a dotted process-step indicating line is drawn across chart 22. The equipment includes multi-pin sockets 58, 59, 60 and 70 which are free of plugs or co-operate with suitably cross-connected plugs according to whether 12-, 6-, 4-, 3- or 2-point working is desired. For 12-point working a plug in 60 connects 1-1<SP>1</SP>, 2-2<SP>1</SP>, &c., and, e.g., for 6-point working a plug in 60 connects 1, 7 and 1<SP>1</SP>, and 2, 8 and 21 &c. so that the biasing is adjusted and the whole width of the chart 22 is utilized. Figs. 3-4 permit 12-, 6-, 4-, 3- or 2-point recording but other numbers of channels may be utilized by alternative switching means, e.g. 16, 8, 4, 2. Selection of a resistor 64 (in series with bias chain 61) by 3-way switch 63 provides a desired sensitivity e.g. 5, 10 or 20 millivolts per inch. Resistors 65 and 66 ensure that the primary of transformer is not open-circuited when the uniselector wipers are between stations or the potentiometer slider 25 is off the end of the winding.