Patent GB-1432674-A (GB)
Title: Adjusting energy systems
IPC: H02P7/292
Filed: 1973-04-10
Abstract: 1432674 Automatic control systems AUTOMATED ENERGY SYSTEMS Inc 10 April 1973 [14 April 1972] 17072/73 Heading G3R [Also in Division H4]  The value of a measured variable in a system is expressed as the period of time between successive pulses in a periodic signal and this is used to gate pulses from a fixed frequency source to a counter in which is set a number corresponding to the desired value of the variable and as long as the gated pulses are below the set number energy is supplied to the system in discrete quantities of equal magnitude. In the embodiment shown the speed of a D.C. motor is detected by the photoelectric arrangement shown, the pulses from which are applied via 483 to a counter 506 to cause it to receive a binary number corresponding to desired speed set on a switch device 507. The pulses also open a gate 487 to pass clockpulses from 486 which are counted down in the counter. If zero is not reached before the end of the pulse this indicates that the speed is too slow and, via memory 508, the counter operates a switch 509 which passes exactly one cycle of a rectified A.C. supply. The rectifier comprises a bridge either of four diodes or two diodes and two thyristors which are triggered at current zero by the switch 509, also Fig. 9, (not shown). The speed may alternatively be measured by a gear-wheel and energized coil forming a variable reluctance device Fig. 5, (not shown). Pressure. The system may control the energization of a pump motor in response to fluid-  pressure measured by a "variable Mu" transformer Fig. 10, (not shown) or a Piezo-electric crystal.  Alternatively a strain gain pressure transducer may be used, the resistance of which is converted into the period between sharp pulses generated by a relaxation oscillator; the resistance varies the charging rate of a capacitor which is discharged by a conjunction transistor Fig. 1, (not shown). The pressure may be that of plastics in an extrusion head. Temperature. This is measured by a temperature sensitive resistor, used in the pulse generating circuit of (Fig. 1) and is controlled by applying individual cycles of an A.C supply to an electric heater, e.g. in a plastics extrusion machine. Alternatively, the temperature of super-heated steam may be controlled, together with any moisture in it, as detected by the absorption of micro-waves. In a micro-wave oven for preparing the most succulent roast known to man the source of microwaves may be controlled in response to the amount which are not absorbed by the load (food or wood). The reference value is varied with time to follow a known curve to produce a desired moisture content. Other variables mentioned are position, light intensity and colour. General. A transducer may be used which produces an analogue voltage output; in this case this is converted to a squarewave signal whose frequency is significant by a circuit Fig. 2, (not shown) in which a ramp signal of constant rate is switched between increasing and decreasing at zero and at a voltage proportional to the trans-  ducer output. This sawtooth wave controls the frequency of the output pulse signal. Many sensors (e.g. 16) and correctors may be associated sequentially with one counter and clockpulse generator, using a multi-plexing system Fig. 7, (not shown). In Fig. 12 (not shown), eight such systems are connected by a second multi-plexer to counters arranged to operate high or low level alarms and to indicate the value of any selected one of the variables. If a transducer is non-linear in its response this is corrected in the digital circuitry by using the signal to address a memory which contains the characteristic of the transducer. It is a feature that the counter causes one cycle only to be applied for correction when it doesn't count down to zero, but the counting is repeated at a high rate to provide substantially continuous control.