Patent GB-1493451-A (GB)
Title: Circuit for a two-coordinate display or recording apparatus
IPC: G01R13/20
Filed: 1975-05-08
Abstract: 1493451 Measuring variations in signals with frequency WANDEL U GOLTERMANN 8 May 1975 [10 May 1974] 19428/75 Heading G1U In displaying a measured signal as one coordinate on a two-co-ordinate display, a display of acceptable tolerance limits in the measured signal is also provided, the tolerances changing between different 'zones' of the other co-ordinate. In the Fig. 4 embodiment, a measured signaly applied to terminal 90 is displayed as a function of frequency on a CRT display 1', the measuring frequency being applied to the input of a frequency-voltage converter 6'. The measuring frequency repetitively monotonically increases to provide the x-time base for the display. The CRT is a single beam two-channel device, the y input 90 and the tolerance limit signals (from A/D converter) 8') being alternately applied 7' to the y deflection amplifier 3' and coil 5'. The tolerance limits and the upper levels of the corresponding frequency 'zones' are stored in respective write/read memories 52, 51 respectively. In the normal 'read' mode, switches 77-78, 61-64 are open as shown. As the input frequency reaches the level stored in the memory 51 at the address selected by whichever gate 69 is enabled by control 11', the comparator 15' receiving the stored value from the memory read outputs 55 via D/A converter 14' produces an 'index' pulse of constant width. The selected address is fed via AND gates 82 to the second control 11" which thus addresses the corresponding tolerance value store 52 to supply the tolerance level via D/A converter 8' to they deflection system. At the indexing pulse, gates 83 isolate the control 11", and pulses from a generator 79 are fed to the control count input and via a bi-  stable 81 to its forward/reverse control. The control 11" thus oscillates between its previous address, and the next address. The memory 52 output 56 thus rapidly alternates between successive tolerance levels to produce a bright trace for the vertical parts of the display. In this 'read' mode, selection of one switch 77, locks the memory 51 address to that selected, and also locks the memory 52 via control 11", so that only one vertical part is displayed. Selection of a switch 78 holds that particular output from memory 52, resulting in a horizontal line across the whole of the CRT image. For writing in the various 'zone' limits and tolerance levels, the switches 61-64 are changed over. Gates 69 are thus blocked, and selection of any switch 77 holds an address and the memory 51. The 'write' inputs 53 are supplied from an UP/DOWN counter 88 also supplying via switch 63 and D/A converter 14' a comparator 65. This receives a reference level from potentiometer 65 and supplies an output to unit 84, which according to the difference signal supplies pulses from generator 86 to the counter 88. Thus, the counter is driven to the level set by the potentiometer, and this is entered in the memory 51 by inputs 53. A similar process applies to setting the tolerance levels in memory 52. In another embodiment, Fig. 2 (not shown), an intensity modulation is used. The x-deflection signal is derived from the frequency as before, but a sinusoidal signal is applied to the y deflection system to provide a tv-type raster. For rising portions of the y-time base (detected by a differentiator, the 'zone' limits are compared with the actual frequency to provide incrementing of the control unit and during falling portions, the tolerance levels are compared with the time base to produce intensity modulation at equality. The actual measured signal is displayed during the rising portions of the y time base. In a third embodiment Fig. 5 (not shown), an external precision generator may optionally be used to set the frequency 'zone' limits.