GB1100263A - Improvements in or relating to alarm systems for flame monitoring - Google Patents

Abstract

1,100,263. Temperature alarm systems. POWER-GAS CORPORATION Ltd. 14 Aug., 1964 [21 Aug., 1963], No. 33026/63. Heading G4N. [Also in Division G1] An alarm device for monitoring a flame in, for example, a furnace comprises a flame sensor for providing an electrical signal containing a fluctuating component representing flame flicker, a transistor amplifier for amplifying the signal and at least one transistor static switch responsive to the amplifier output to actuate audible and/or visual alarm means in response to the disappearance of the amplifier output (i.e. of the flame). A number of such devices may be used together in a system to monitor different flames in a furnace. In one device (Fig. 1, in which unconventional base bias circuit is not shown) the sensor is a photo-conductor element R s . Alternatively, a photovoltaic cell (Fig. 2, not shown) or a probe element in direct contact with the flame (Fig. 3, not shown), is used. The detector R s receives radiation focused on to it from the flame by a lens system L and the resulting variations in its resistance are transmitted as a small varying current to transistor T 1 . The D.C. component of the amplified signal is filtered by network C 1 , C 2 and R 2 leaving an A.C. signal dependent on the flame flicker. As a result the transistor T 2 acts as a static switch in the " off " position due to the reverse biasing effect of the positive half cycles of this signal. When the flame is extinguished, the transistor T 2 conducts and the lamp S lights. In an alternative arrangement using a photo voltaic cell (Fig. 5, not shown), the filter circuit comprises a capacitance and a diode. In a system in which three separate flames are investigated (Fig. 4, not shown) three devices, as in Fig. 1 or 5, are used together with corresponding transistor switch arrangements (2T, 3T, 5T) and common switch (4T). On the initial extinction of any one flame (I), a signal is obtained from the switch (1T), resulting in the horn (H) sounding and the flasher unit (K) being actuated. Further, another switch (3T) is switched on, but the intermittent blocking signal from (K) causes the lamp (S) to flash. Depression of the required button (B) cuts off the flasher unit and horn and a steady glow from the signal lamp (S) is obtained.