Hawker Alarum Manual

Operating Principle
The Alarum supplies a small electrical pulsed current to the electrodes, and detects a change in
the current when an electrically conductive liquid touches the measuring electrodes. A small
pulsed current is used to prevent electrolytic action between electrodes. When the presence
of a liquid is detected the Alarum either de-energises or energises its internal relay dependent
on the internal factory programmed fail-safe setting, providing the user with a set of volt free
S.P.C.O contacts. The internal relay is de-energised in alarm and energised when the alarm is
reset. The unit has 2 electrodes, the active referred to as the 'P1' and the common 'G'.
The electrical connections are made to the terminal connectors located under the screw on cap.
Always check to ensure the controller specifications are suited to the supply and its application
before installing. The 2-way terminal block is for the connection for the incoming DC power
supply this is marked +V and –V.
The 3-way terminal block provides the volt free relay output changeover contacts for control or
alarm indication.
Mounting the Alarum
The Alarum should preferably be mounted vertically in the vessel. Spacing between the
electrodes and their distance from the side of the vessel is dependent on the likelihood of
bridging due to floating matter and the degree of turbulence.
Using plastic coated electrodes (which can be specified on ordering), can eliminate bridging,
always bare at least 50mm of the coating. The Alarum is mounted using either a fixing collar
or BSP thread depending on the diameter of factory fitted electrodes. A full range of mounting
hardware is available from Hawker Electronics Ltd. The installer must fit a cable gland
suitable for its intended environment.
When mounting ensure that the electrode holder insulators protrude through the surrounding
material e.g. concrete floors, this is to prevent the electrodes finding a conductive path through
the concrete and not the liquid in the vessel. It is advisable to clean electrode rods and
insulators at periodic intervals.
The fail safe setting is factory set and is specified on order. This will be indicated in its internal
label as either FSH (High) or FSL (Low). Removing the screw on cap will reveal the power
and volt free contact terminals.
The Alarum can be tested initially for basic operation by placing a short circuit and open circuit
across its electrodes. The relay contacts can be checked with an ohmmeter or similar.
Fail Safe
High
Fail Safe
Low
Alarum
Electrodes Relay contacts
Open circuit C & NO should be closed (short circuit)
C & NC should be open (open circuit)
Short circuit C & NO should be open (open circuit)
C & NC should be closed (short circuit)
Electrodes Relay contacts
Open circuit C & NC should be closed (short circuit)
C & NO should be open (open circuit)
Short circuit C & NC should be open (open circuit)
C & NO should be closed (short circuit)