| 摘要 |
<p>1484827 Temperature control MULTI-STATE DEVICES Ltd 28 Nov 1975 [29 Nov 1974] 49048/75 Heading G3R [Also in Division G4] A heater control system comprises a temperature discrimination apparatus (see Division G4) for determining when a predetermined temperature has been reached, such apparatus comprising, as shown in Fig. 3, a switching device Rl exhibiting regenerative switching action at a power level dependent upon temperature and connected in series with a resistor R2 across an A.C. supply, and a switching device D1, a silicon unilaterial device as shown, exhibiting regenerative switching action solely in response to a preselected power level. In operation, the point at which R1 switches varies from 90 degrees to 0 degrees proportionally as temperature increases, and the point at which Dl fires is set by resistor R3. As long as the temperature is below the predetermined temperature, D1 fires before R switches and a sharp pulse appears across resistor R6. Similar action occurs on each successive cycle and thus a series of pulses are applied to fire a SCR Ql which controls the firing of a triac TR in series with the heater H. When the predetermined temperature is reached R1 switches first and thus a diode D2 becomes forward biased thereby lowering the voltage across R3 so that D1 does not fire and no pulses are applied to the SCR Q1.</p> |
