Abstract: A carbon monoxide gas detector comprises a housing consisting of two enclosures 10 and 12 having ports in the wall thereof to provide a tortuous path for air entering the inner enclosure 12. A gas cell transducer 16 connected to an electrical circuit 18 provides signals indicative of gas concentration. The detector is powered from a remote supply via wires 22 and 26 and provides gas concentration signals via a wire 24 to a remote central station with a fail-safe feature wherein failure of the circuit or the detector will provide signals interpreted as dangerous gas concentrations.

Abstract: A slack rope detecting apparatus for use in mine winding operations provides a trip signal via contacts 34 if the load in the rope falls below a predetermined value. The apparatus senses the load at each side of a sheave wheel using transducers 6 and 8 and uses a mean value of their outputs as an input to a summation amplifier 12. The weight of the rope between the sheave wheel is compensated for by monitoring rotation of the winding engine drum 42 and providing corresponding input signals for the amplifier 12. When the effective load in the rope falls below a predetermined value, set by input 28, a trip signal is produced. The trip signal output is preferably visually displayed and recorded.

Abstract: An alarm system which includes at least one primary detecting device that provides an analog output signal. The rate of change of the analog output signal is monitored, and an alarm signal is generated when the rate of change exceeds a preset limit. The analog output signal is also compared with a first reference level signal to provide a pre-maintenance warning signal when the analog output signal reaches the first reference level.

Abstract: A single chamber ionization-type fire detector. The ionization current is directly amplified to provide a usable analogue signal by means of an operational amplifier which has a minimal effect in the ionization current. The operational amplifier is simultaneously employed to maintain a constant potential difference in the chamber so that the ionization current is not subjected to a fluctuating voltage. The amplified analogue signal drives a recorder and through analysis of the recorder output genuine fire alarm conditions can be distinguished from false alarm conditions.

Abstract: A method of monitoring the rate of change of a first signal which includes the steps of periodically sampling the first signal, generating a first reference signal which for each period differs from the sampled amplitude of the first signal by a predetermined amount, comparing the amplitudes of the first signal and of the first reference signal, and generating an output signal when the amplitude of the first signal crosses the amplitude of the first reference signal.The invention also provides apparatus for monitoring the rate of change of a first signal which comprises means periodically to sample the first signal, means to generate a first reference signal which for each period differs from the sampled amplitude of the first signal by a predetermined amount, and means to compare the amplitudes of the first signal and of the first reference signal and to generate an output signal when the amplitude of the first signal crosses the amplitude of the first reference signal.

Abstract: The invention provides apparatus for testing the condition of a battery comprising a load, means to connect the battery to the load for a predetermined interval and means to measure the battery voltage at least at the end of the interval.The invention further extends to apparatus for successively testing the condition of a plurality of batteries comprising means for connecting one of the batteries to a given load for a predetermined interval, means for measuring the voltage of the battery at least at the end of the interval, means for determining the condition of the battery from the voltage measurement, and control means for connecting a fresh battery to the load and repeating the testing of the batteries until all the batteries are tested.The invention also provides a method of testing the condition of a battery including the steps of connecting the battery in a charged condition to a load for a predetermined interval, and measuring the battery voltage at least at the end of the interval.