Patent GB-1237395-A (GB)
Title: Improvements in display apparatus
Inventor: LIGHT LEON HENRY
IPC: A61B5/02
Filed: 1968-03-27
Abstract: 1,237,395. Cathode-ray tube displays. NATIONAL RESEARCH DEVELOPMENT CORP. 26 June, 1969 [27 March, 1968], No. 14773/68. Heading H4T. In an arrangement for indicating the magnitude of a characteristic of an electrical signal as a marked position on a trace produced on a cathode-ray display tube, the electrical signal is employed to momentarily increase or decrease the magnitude of an oscillatory waveform at a time, in each period of a time base signal applied to the tube, determined by the magnitude of the electrical signal, the oscillatory waveform producing a trace against the timebase deflection and the position at which the increase or decreases occurs in the trace being indicative of the magnitude of the electrical signal. Thus, as shown in Fig. 1, which utilizes a twobeam cathode-ray display tube 14 on which the magnitudes of four different characteristics are indicated, the four electrical signals are applied to respective comparators 17, 24, 25, 26 together with the horizontal time base waveform of the system which is standardized in a network 16. Each comparator produces an output signal when equality occurs between its two inputs and these output signals are shaped in respective circuits 18, 27, 28, 29 and further shaped by respective diodes 19, 30, 31, 32 which produce substantially triangular pulses, the diodes 19 and 31 producing positive pulses and diodes 30, 32 negative pulses. The positive pulses are fed to respective limiters 20, 21 and the negative pulses to respective limiters 22, 23 connected as shown to a source of oscillations 35 supplying a waveform as shown in Fig. 2a which, in the absence of the input pulses, is limited at fixed upper and lower limits as shown at 37 (Fig. 2b). The limited waveform is applied to the vertical deflection means of the display tube (or employed to produce a "vectorscope" type of display, by comparing the limited waveform with the time-base waveform and utilizing pulses produced when equality between the two waveforms is reached to unblank the tube beam which is deflected in the vertical direction by a high-frequency waveform) and produces a trace comprising a horizontal bright band such as shown at 40 (Fig. 5). Considering the operation with one of the two beams, when input pulses are applied to the limiters the clipping levels are momentarily increased as shown at the end of the period 37 in the negative direction for input pulses to limiter 22 and as shown at 38 for input pulses to limiter 20 and this action results in a broadening of the trace in the form of "half-arrows" 42 and 41, respectively, the position of which with respect to the commencement of the trace are indicative of the magnitudes of the corresponding characteristic being measured. A scale 43 may be fixed to the tube screen and one end may be provided with a red filter to indicate a danger limit. The second beam produces "half-arrow" markers at the upper and lower edges of its trace in similar manner in response to input signals at terminals 12 and 13 and, if desired, more than one comparator and shaping circuit may supply input pulses to the same limiter (Fig. 4, not shown). Thus, in Fig. 5, the markers 41 and 75 may indicate diastolic and systolic blood pressure and the marker 42 the mean heart rate when the invention is employed, as intended, in coronary-cure stations and the other beam (beams, if more than two) may be utilized to display an ECG waveform 76 and pulse pressure waveform 77. Circuit details of the network 16, the comparators 17, 24, the shaping circuits 18, 27, the limiters 20, 22 and the oscillatory source 35 are described with reference to Fig. 3 (not shown).