Patent GB-1088976-A (GB)
Title: Apparatus for detecting and measuring signals
IPC: G01N27/64
Filed: 1966-03-03
Abstract: 1,088,976. Ionization gauges. ETABLISSEMENT POUR APPLICATIONS ELECTRONIQUES. March 3, 1966 [March 11, 1965], No.9307/66. Heading G1N. [Also in Division H3] The pressure, density or degree of purity of gases, vapours or fumes, is measured by a circuit consisting basically of two ionization chambers 1, 2, Fig. 1, the former being a hermetically sealed reference chamber and the latter the measuring chamber, connected in series to form a potential divider to a supply source 3, the common point 4 between the chambers being connected to the gate electrode 8 of a metal oxide semi-conductor device 9. By adjusting the separation of electrodes 5, 6 of the reference chamber, the potential of the point 4 and therefore of the gate electrode can be arranged so that the transistor 9 operates in the middle of the linear part of its characteristic.  In one embodiment, Fig. 1, the circuit also includes a meter 11, e.g. a galvanometer or relay, which measures the current flowing through the source circuit of the M.O.S. device. Resistances 12, 14 and a negative temperature coefficient resistance 13 form a network compensating for temperature variations of the M.O.S. device. A load 10, which may be an alarm circuit, a wire or wireless remote control circuit or an electric load in general which is required, may be inserted either in the source or drain circuit of the M. O.S. device. In a modification of this circuit, Fig. 2 (not shown), the common point 4 is connected to the gate electrode of a double-gated M.O.S. device (15), the load resistance (17) being connected in its source circuit, while a positive temperature coefficient resistor (18) is placed in its drain circuit. Voltage variations across the load (17) are then applied to the base of a transistorized amplifier (19), whose output circuit comprises a meter (20) and an adjustable threshold relay (21). A temperature compensating network (22- 24) determines the operating point of the amplifier (19). In a modification of a circuit of Fig. 2, the amplifier is replaced by a solid-state pulse generator consisting of a thyratron or thyristor (25), Fig. 3 (not shown), and diode (26). A potentiometer (27), inserted in the drain circuit of the M.O.S. device (15), is used to adjust the threshold of a thyratron (25). When the current reaches a sufficient value to strike the thyratron (25), it conducts and supplies a load inserted between the terminals (31, 32) with a pulse. The sudden establishment of current is transmitted through the diode (26) to the external circuit through resistances (29, 30). An arrangement for supplying differential measurements to a meter (20), Fig. 4 (not shown), which is connected to the output of an amplifier (36), comprises two basic circuits with ionization chambers (1a, 2a, 1b 2b) and M.O.S. devices (15a, 15b). These circuits are connected across the terminals of output resistors (33, 34) which are also connected to the amplifier (36). A potentiometer (35) balances the arrangement. In a bridge arrangement, Fig. 5 (not shown), two sets of ionization chambers (1a, 2a, 1b 2b) and associated M.O.S. devices (15a, 15b) are connected in opposition, so that a measuring meter (20) connected across the output terminals, will indicate whether the gas tested is lighter or heavier than the reference gas, the M.O.S devices reacting in opposite senses for gases lighter or heavier than the reference gas. Two thyristors (39a, 39b) whose operating thresholds are adjusted by means of potentiometers (37, 38) will strike when the densities of the gases have reached or exceeded a predetermined degree, to supply a pulse to any load which may be inserted in series with each of the thyristors.  In all these embodiments, the measuring chamber consists of a cylindrical perforated electrode with a central electrode which carries the radioactive charge.