GB691880A - Calibrating apparatus, particularly for an electrocardiograph - Google Patents

Abstract

691,880. Electrocardiographs. CAMBRIDGE INSTRUMENT CO., Inc. Feb. 26, 1951 [Feb. 25, 1950], No. 4626/51. Class 81 (ii). Electrocardiograph calibrating apparatus comprises an amplifier indicator including a record medium and having means for advancing a record trace with respect to the record medium and indicating the magnitude of an input voltage as a function of time, a standard source of potential coupled by a first circuit to the input amplifier circuit with a first polarity, the first circuit being normally open at a vibratable reed for periodically connecting the standard source to the input circuit, whereby the actuation of manual means for initiating vibration of the reed produces a trace indicating the amplification of the amplifier and having time calibrating marks denoting the speed of the trace advancing means. The patient is connected across input terminals 4, 5 so that fluctuating patient' voltages pass through a two-stage push-pull amplifier 6 which is connected by sensitivitycontrol potentiometers 106, 108 with a vacuumtube bridge circuit 8. The amplified signal voltages produce unbalance in the bridge circuit 8 so that current passing through a galvanometer coil 192 causes deflection of a stylus 14 of recording apparatus 12. The stylus 14 moves over a chart paper 16 which is moved past the stylus 14 by an electrically driven roller 196. In order to calibrate the recording apparatus 12 with respect to time and voltage, a lever 20 of calibrating apparatus 18 is manually rotated to deflect a weighted reed 244 and thus set it in vibration and to enable the calibrator circuit to be made by closing contacts 254, 256. The reed 244 oscillates between two contacts 266, 274 so that calibrating voltages from a standard cell 262 are periodically reversed at the same frequency as oscillations of the reed 244 and have a substantially square wave form and are passed through the amplifier 6 and the bridge circuit 8 to be recorded on the chart paper 16. The stylus 14 may be in the form of a pen or may be heated to produce a visible trace on heat-sensitive paper.