Monitoring appts. for indicating losses of stored material - has level sensor and circuitry for discriminating between level changes due to demand or supply and those caused by e.g. leakage

摘要

The appts. comprises a level sensor (7) providing an electrical output the value of which is read into an instantaneous store at predetermined time intervals under the control of a timer. A pulse shaper is connected to the instantaneous value store and provides a pulse output indicative of the rate of rise or fall as measured by the level sensor. Alarm circuits operate in response to the output of the pulse shaper via respective threshold switches to indicate optically and/or acoustically unauthorised changes of level as measured by the sensor (7). An arrangement is provided for inhibiting the alarm circuit when the monitored liquid level is being altered by authorised addition to or subtraction from the stored liquid.