Patent GB-1417149-A (GB)
Title: Physiological data sensor-transmitter
IPC: G08C19/00
Filed: 1972-11-16
Abstract: 1417149 Pulse modulation circuits MONITRON INDUSTRIES Inc 16 Nov 1972 [17 Nov 1971 18 Nov 1971 (2)] 53022/72 Heading H4L [Also in Division G1] In a combined sensor/transmitter, e.g. for measuring the temperature of the allixid. the sensor and transmitter are mounted in a casing which is provided with an adhesive pad for securing to the body to be tested. Casing 32 of a rigid plastics material is provided with a receptacle 42 in which a thermistor sensor (not shown) is mounted by means of an epoxy heat insulating material, the thermistor leads extending through holes 50, 52 into the interior of the casing where they are connected in a battery operated transmitter contained therein. Physical details of the transmitter and antenna are described, Figs. 6, 7 (not shown). Casing 32 is also provided with opening 36 through which the battery is inserted, and a switch receptacle 54. Casing 32 is snap action mounted in a cavity 88 of a soft flexible cover 84 so that the bottom surfaces 86 and 34 are flush with one another and then a double-faced adhesive pad 90 including openings 110, 112 aligned with apertures 54, 42 in the casing 32 is attached to surfaces 86, 34. A switch cover, Figs. 3, 4 (not shown) is then pressed into position in receptacle 54 through opening 110 to non-reversibly switch on the apparatus and after removal of paper layer 104 the then exposed adhesive layer is positioned in the required position on the subject with the thermistor extending through opening 112 into firm contact with the subject's skin. Transmitter circuit, Fig. 8,-is in the form of a blocking oscillator producing recurring bursts of R.F. frequency signals, the rate of which bursts is controlled by the resistance of thermistor 192, the circuit being designed so that a very narrow frequency spectrum is produced during each burst. Upon closure of switch 205 by the switch cover tank circuit 18, 164 is excited into a resonant oscillation, Figs. 10, 11 (not shown), and capacitor 128 in the feedback circuit to the base of transistor Q1 begins to charge negatively. When capacitor 128 has charged sufficiently so that the average D.C, level thereon is such that the positive voltage swings in the tank circuit are insufficient to cause the transistor to conduct the oscillations diminish exponentially until they finally stop. During the course of the burst the positive collector voltage is fed via diode 132 to storage capacitor 203 and at the end of the burst the voltage thereacross starts charging capacitor 128 positively through thermistor 192. When the capacitor 128 is charged sufficiently positively the transistor conducts and another burst is initiated. Thus as the resistance of thermistor 192 changes with the variations in temperature of the subject so does the charging rate of capacitor 128 and hence the period between the bursts, the relationship between temperature and pulse rate being nearly linear. In a modification, Fig. 14 (not shown), diode 132, capacitor 203 and resistor 204 are omitted and the thermistor is connected between top 200 and the base of transistor Ql. A non-self-exciting circuit may be obtained, Fig. 15 (not shown), by interchanging capacitor 203 with diode 132. Excitation is obtained by means of an external transmitter. Although the circuit is designed to operate until the battery wears out it may be stopped by placing the unit on a plate of conductive material. Receiver, Fig. 1 (not shown), is a hand held portable digital indicator and is such as to pick up the R.F. bursts at a range of 3 to 7 feet. The signals are picked up by a loop antennae and converted into square wave signals at the audio frequency of the pulse modulation. The square waves are fed to a logic circuit which gates a clock pulse generator connected to a counter.