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(11) | EP 0 066 418 A3 |
(12) | EUROPEAN PATENT APPLICATION |
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(54) | Sound operated start circuit |
(57) The invention is concerned with starting of electrical machines from a sound emitting
device and is particularly concerned with safety circuits for the start of a coal
getting machine on the sounding of a klaxon giving warning to mine workers underground
that the machine is to be started and hence to keep clear. The signal from the klaxon
is detected as to certain predetermined parameters including amplitude, frequency
and the rate at which the klaxon is being operated since it would normally be controlled
by a water driven pump. The signal is then fed to a discriminator circuit which then
determines that these parameters are correct. Two such circuits are provided in parallel
with each other and a signal to enable the machine to be started is only provided
at an output terminal when the correct signal is found and detected by both circuits
simultaneously. |