Under-voltage protection for thermal imaging camera power supply, has supply transferred to intermediate battery tapping, so actuating camera safeguarding unit, if battery voltage falls

摘要

The camera (1) has electronic circuits (2) under the protection of a safeguarding unit (3) which isolates the camera if the supply voltage (Vc) falls below a predetermined threshold, typically 7.5v. The supply is provided by a power pack (4) containing a nickel/metal hydride series-connected battery (5) having a cell voltage of 1 v, the full 11-cell battery normally in service. Supply voltage is also monitored by a check unit (6) connected across the battery (B-D), whose output (O) controls a change-over relay (7). This normally applied (o-a) the full battery to the camera, but if the voltage falls below a second threshold value, e.g. 11 v, the check unit, through the relay (o-b), connects the camera to an intermediate tapping (C) giving an 8v output. With a declining battery condition a relatively short time will then elapse before the voltage falls below the safeguarding threshold of 7.5v and the camera is disconnected. The original supply connections are restored by an automatic resetting feature when the battery is recharged or replaced.