Patent GB-1501931-A (GB)
Title: Bar display with multiple indication
IPC: G01R13/40
Filed: 1976-04-15
Abstract: 1501931 Indicating apparatus HONEYWELL Ltd 15 April 1976 [15 Jan 1975] 1786/75 Heading G1J [Also in Division G4] A bar display system for indicating as distinctive lengths of a bar of light the magnitudes of two input signals B, S includes circuitry which imposes on the display one brightness pattern from zero to the value of the smaller input signal and a second brightness pattern between the respective values of the two signals in a manner such as to indicate which of the two signals is the greater. Thus both values, and the difference between them are clearly visible on a single bar display. The system includes a bar display device 10 in the form of a flat bar-like gas-filled space having a transparent anode 11 on its inner front face and 200 equally spaced cathodes 12 on the back face, the cathodes being connected in three inter-digitated sets 13, 14, 15. A keep-alive anode 18 and cathode 17 and a reset anode 16 are provided at one end of the space. A clock signal generator 20 drives a  display drive circuit 21 to energize each set of cathodes in turn. A ramp signal generator 30 driven by the clock signal generator 20 supplies a ramp signal to comparators 40-42 which form part of a logic circuit 40-48 controlling an anode drive circuit 33 for the anode 11. Input signals S, B are applied to comparators 40, 41 respectively, the anode drive circuit 33 being energized via an OR gate 43 so long as either signal exceeds the instantaneous value of the ramp signal to produce, in conjunction with the cyclic energization of the cathode sets 13-15, a visible discharge stepping rapidly along the display to appear as a bar of light of length representing the magnitude of the larger of signals S, B. A divide-by-200 circuit 22 sends a reset pulse to the ramp signal generator 30 and the display drive circuit 21 once per 200 pulses from the clock signal generator 20. A divide-bythree circuit 35 driven by the clock signal generator 20 controls a flip-flop 36 the output of which is applied to one input each of AND gates 44, 47. The AND gate outputs are connected via an OR gate 48 to the anode drive circuit 33. The comparator 42 compares the inputs S, B and provides an enabling signal to the AND gate 47 when S>B and to AND gate 44 when B>S. The anode drive circuit 33 is controlled by the logic circuit 40-48 so that when S>B the bar of light displayed is banded up to the value of B and solid thereafter up to the value of S. If B > S the bar is solid up to the value of S and banded thereafter up to the value of B. The bands, alternately bright and dim and each the width of three cathodes 12, derive from the flip-flop 36, and move along the bar of light. If the circuit units 35, 36 are omitted, the two sections of the light bar are bright and dim respectively.  In a modification, Fig. 2 (not shown) where one input signal is a measured value and the other is a reference signal, a bright line is produced on the display at the level of the reference signal, the lower part of the light bar is dim, and the deviation of the measured value from the reference value is shown as a bright band above or below the bright line, to indicate the sign and magnitude of the deviation. The circuit units, 35, 36 may be included so that the deviation is shown by a banded section, the bands moving towards the reference bright line.