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1. Introduction
The Mobrey Electropulse system is used for the detection of liquids or liquids with suspended / settled
solids. It consists of three units, a sensor, a head amplifier unit, and a control room unit.
1.1 Sensors
There are many different Mobrey sensors available, but they fall into two categories:
a) Gap sensors
Gap sensors feature two ultrasonic transducers mounted one either side of the gap. When immersed in a
liquid the signal transmitted is carried by the liquid across the gap, to the receiver, when the liquid level
drops below the sensor, the signal cannot be carried across the gap, and is not received by the second
transducer.
b) Hi-Sens cylindrical sensors
Figure 1.1 - Gap sensor, cut away to show construction
The Hi-Sens sensor consists of two ultrasonic transducers mounted
on the inside of a cylinder. When the sensor is not submersed in
the liquid the signal from one transducer resonates round the
cylinder like a bell ringing. If the liquid rises up around the
sensor, this ringing is damped and the signal received by the
second transducer is significantly reduced. This reduction is
monitored by the head amplifier unit. Switching occurs when the
liquid is about half way up the cylinder.
Figure 1.2 - Hi-Sens, cut-
away to show
construction
Use of Hi-Sens transducers in high alarm applications, and gap
sensors in low level alarm applications achieves a Failsafe system
in which any sensor or cable failure will be indicated as a fault or
an alarm by the control unit.