| 摘要 |
The detector (R) is formed of a spiral of thin platinum alloy wire enclosed in a Davy cage of fine metallic grids to prevent flame propagation in the event of ignition within. It is connected in a bridge circuit with potentiometer (R3) and two fixed resistor (R2, R4), supplied with rectified AC from a series transistor (T1) and Zener diode stabiliser (Z1). The unbalance of the bridge is monitored by a differential amplifier (Ad) which controls a low-frequency tone generator (IC2). When the threshold of unbalance is exceeded due to a concn. of gas within the detector, an alarm is given by an electroacoustic device (TA). A standby battery and delay circuit may be provided to ensure operation following failure of the AC supply or rectifier. |
