Patent GB-1082803-A (GB)
Abstract: 1,082,803. Switching and timing circuits; analysing sounds. THIOKOL CHEMICAL CORPORATION. Oct. 26, 1964 [June 19, 1964], No. 43554/64. Headings H3T and H4D. [Also in Divisions A5 and G4] In a system for monitoring heat beats (see Division A5) circuits are described for (a) detecting and integrating spurious signals occurring in periods which should be quiet, (b) detecting and integrating gaps in normal signals, (c) indicating when these integrated values exceed a predetermined level, and (d) synchronizing the circuits according to the basic frequency picked up by an electrocardiograph. Synchronizing circuits.-The signal from the electrocardiograph is amplified with a bandwidth of 0À2-100 c/s., adjusted in gain and polarity if necessary (Fig. 2, not shown), base-clipped and applied to a Schmitt trigger to generate a synchronizing pulse (158 in Fig. 3, not shown). This triggers two monostable circuits (201, 202) the latter of which triggers a third monostable circuit (203) by its trailing edge. The outputs of these circuits are combined in pairs in gates (205, 206) to provide the necessary synchronizing signals. A fourth monostable circuit (207) is also triggered by the trailing edge of circuit (202) to provide a control voltage to alter the unstable periods of the other three monostable circuits if the cardiac rate changes. The circuitry of this arrangement is shown in Fig. 4. The synchronizing pulse 158 triggers the monostable circuit 202 (comprising transistors 225, 226) to its unstable state, passing a signal through diode 251 to the gate 205. A similar monostable circuit 201 provides the second input to this gate via diode 254. The fourth monostable circuit 207 (not shown, but triggered from the trailin gedge of 202) feeds an integrating capacitor 230 which is also supplied in opposition from 202 via resistor 229. These normally balance so that the net change in voltage on 230 is zero, but if the cardiac rate changes one of these pulses will be of greater duration and a voltage signal will be applied to transistor 235. The output of this transistor is fed via amplitude control 236 (to introduce a time delay) to an amplifying transistor 237. The gain of this is low for signals below a threshold level set by potentiometer 241 but high for signals exceeding this threshold. The output of transistors 235 and 237 control the unstable periods of the four monostable circuits (a) 202 direct via resistor 239, (b) 207 at reduced amplitude via lead 242, and (c) 201 and 203 via amplifiers 246, 249 and threshold-setting potentiometer 247 to cut-off signals below 100 per minute. Detecting spurious signals.-Signals from the amplifier are amplified with pre-emphasis of 120-140 c/s., set to a definite level and rectified (Fig. 5, not shown) before being applied to transistor 302 (Fig. 6). Normally, capacitor 305 is shorted by transistor 306, but when the gate 205 (see above) turns on 307, 306 is cut off, and during these periods any heart signals above a threshold set by resistor 304 cause periodic conduction of transistors 302, 303 and accumulation of charge in capacitor 305. At a certain level of capacitor voltage, transistor 311 will conduct and trigger bistable circuit 314, 315 to apply a signal to the display and counter unit (see below) and light lamp 319. The bi-stable circuit is reset by a pulse from the monostable circuit 201 (see above). Detecting gaps in signals.-The rectified heart signal is also applied via a low-pass filter to transistor 326 (Fig. 7), whose output is shorted by transistor 327 except when gated by a signal from monostable circuit 203 (see above). When this happens, Schmitt trigger 328, 329 passes into its second state, but returns to its first state during any interruptions of the signal. Such a change is passed on through capacitor 330 to a monostable circuit 332, 333 which then generates an output signal to charge capacitor 335. The change of the Schmitt trigger is also passed to transistor 340 which will conduct if transistor 341 is also gated on by simultaneous conduction of all three diodes 342-344. Diode 342 conducts when the monostable circuit 332, 333 is activated. Diode 343 conducts when capacitor 335 is charged to a predetermined level. Diode 344 conducts when transistor 340 triggers a bistable circuit 345, 346 but is cut-off by the latter changing over so that a second gap in the signal will not open the gate until the bi-stable circuit is reset in the next cardiac cycle by monostable circuit 201. The output of the bi-stable circuit 345, 346 applies a signal to the display and counter unit and also lights a lamp 350. Display and counter unit.-Means are provided for indicating in how many cardiac cycles one of the above faults occurs. Signals from the bi-stable circuits in the three above units are passed through diodes 363-5 (Fig. 9), to cut off transistor 385 whenever a cardiac defect occurs. The differentiated output of monostable circuit 202 is applied to transistor 379 to control an electromagnetic counter 377-8 to indicate the total number of cardiac cycles investigated and to transistor 381 to control (via transistors 384, 385) a second counter 382-3 to indicate how many of these cycles have defects. Switch 386 is set to the desired number of cycles to be investigated, and switch 388 is momentarily closed to energize relay 389. Contacts 389-2 connect pulsating current to all the counters to set them to zero. Contacts 389-1 set bi-stable circuits 395, 396 and 397. Switch 388 is now opened to deenergize the relay. Bi-stable circuit 395 is reset and blocks transistors 380 and 384 to permit both counters to start. On the conclusion of the desired count in 377-8, bi-stable circuit 395 is again set either directly or via further bistable circuits 396, 397 according to the setting of switch 387. Counting may be stopped at any time by momentarily opening switch 399. Lamps 401 and 402 indicate the state of the bistable circuit 395. The counters may be controlled by further bi-stable circuits operated, e.g. by a frequency meter responsive to the synchronizing pulses 158 to show when the cardiac rate is excessively low.