| 摘要 |
955,976. Automatic control systems. LEEDS & NORTHRUP CO. July 12, 1960 [Sept. 14, 1959], No. 24324/60. Heading G3R. In an automatic control system for maintaining the magnitude of a condition at a selected value currents representing respectively the actual magnitude of the condition and the desired magnitude transverse a resistor in opposite senses and a final control element responsive to the potential difference across the resistor varies the magnitude of the condition in a direction to reduce the said potential difference to zero. As shown, a condition such as the temperature of a furnace 10 is detected by a thermocouple 11 connected to a voltage-to-current converter 12 the current output from which flows in a branch circuit including resistors 15 and 16. A second current derived from a supply 20 and an adjustable resistor 18 related to the desired furnace temperature and opposing the first current, is also passed through the resistor 15 so that the resulting potential difference E prop. across resistor 15 is proportional to the difference between the actual and desired values of the temperature, E prop. being zero when the temperature is at the set point. This deviation voltage, which has a polarity depending on which of the two currents traversing resistor 15 is the greater, is applied to the contact 46a of a vibrator 46 which is driven at a suitable frequency and which has another contact 46b connected to a negative feed back voltage derived from the input circuit of a magnetic amplifier 61 controlling energizing current for the heating resistor 37 of the furnace 10. Operation of the movable pole of vibrator 46 produces an output voltage having an alternating component proportional to the difference between the deviation voltage and the feedback voltage; this output is converted into a direct current by a circuit comprising amplifier 45, coupling transformer 48 and phase sensitive demodulator 49 and then applied to a transistor amplifying stage 50 feeding, over conductors 58, 57 and feedback resistor 60, the magnetic amplifier 61. The provision of the negative feedback voltage ensures that the output current in conductor 58 is maintained proportional in magnitude to the deviation voltage, and an adjustable resistor 66 is included in the feedback circuit to vary this proportionality. The system may include a rate action, there being provided a rate capacitor 39 and a rate resistor 40 which can be brought into circuit with the resistor 16 by closing a switch 38 whereby a voltage E rate, representative of the rate of change of the furnace temperature, together with the voltage E prop. appears at the contact 46a. The system may be used to control one condition having a predetermined relationship to another uncontrolled condition (Fig. 2, not shown), or may be cascaded to allow for fluctuations in the control agent, e.g. the heating resistor supply source, (Fig. 3, not shown). Specification 865,224 is referred to. |
