Patent GB-1393657-A (GB)
Title: Strip chart recorder with marking system
IPC: G01R17/00
Filed: 1973-08-01
Abstract: 1393657 Recording apparatus LEEDS & NORTHRUP CO 1 Aug 1973 [11 Aug 1972] 36611/73 Heading G1J [Also in Division G2]  Apparatus for recording an input signal V IN  on a strip chart comprises a drum 10 rotatable by a motor 16 and carrying a helical element 12, marking means 14 extending lengthwise of the drum so that as the chart moves relative to the drum in a direction normal to the drum axis of rotation, between the drum and the marking means, the chart is marked when the marking means is energized, means 23-28 and S1 for establishing two periods synchronized with the rotation of the drum 10, a source 32 Fig. 2 or 84 Fig. 3 of a reference signal V REF , means for generating a first signal during the first of said two periods representing a function of one of the input and reference signals, means for generating a ramp signal during the second period representing a function of the other of the input of reference signals and the elapsed time during the second period, means 38 Fig. 2 or 92 Fig. 3 for detecting when in the second period a predetermined relationship between the ramp signal and the first signal occurs, and means 40 operable by the detecting means 38 or 92 to energize the marking means at the occurrence of said relationship. As shown, the marking means 14 comprises a bar movable towards the drum 10 by energization of a solenoid 22 to mark a pressure-sensitive paper chart. Alternatively Fig. 5 (not shown) a latent charge is stored on a dielectric chart (112) passing between a bar electrode (110) and a helical electrode on the drum (10) when the electrode (110) is energized. The charge is converted to a visible mark by charged toner particles, using an electrographic system (see Division G2). Cams 28, 30 are driven at half the speed of the drum 10, cam 28 actuating a switch Sl to determine the first and second periods, each of which is slightly less than the time taken for one revolution of the drum 10, and cam 30 momentarily closing a switch S2 once per two revolutions of the drum. Control circuits. In Fig. 2, during the first period the analogue input signal V IN  is applied to an integrating amplifier 36 including a capacitor 44, the output voltage V 2  representing a function of V IN  and elapsed time in the first period. During the second period, the D.C. reference voltage V REF  is applied to the amplifier 36, the output voltage V 2  representing a function of V REF  and elapsed time in the second period. When V 2  reaches a predetermined level, e.g. zero, at a time in the second period dependent on the value of V IN , a comparison amplifier 38 triggers a monostable multi-vibrator 40 which energizes the solenoid 22 to mark the chart. At the end of the second period switch S2 closes to discharge the capacitor 44. If desired, V REF  and V IN  may be applied during the first and second periods respectively. In Fig. 3, the input signal V IN  is applied to an analogue-to-digital converter 82. During the first period, switch S1 enables gates 86 so that the converter output pre-sets a counter 80. During the second period, switch S 1 enables a gate 90 via an inverter 88 so that a reference signal from an oscillator 84 causes the counter 80 to continue. When the counter reaches zero or a full count, a NOR gate 92 is enabled to trigger the monostable multi-vibrator 40. In Fig. 4, (not shown), the input voltage V IN  is converted to a frequency signal by a voltage to frequency converter (100). An up-down counter (98) is used, which is reset to zero when the switch S2 is closed. In the Fig. 3 and 4 systems, the oscillator 84 is used to provide the drive for the motor 94 which turns the drum 10, a frequency divider 96 and power amplifier being interposed between the oscillator and the motor.