MN301520 Rev A1
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Application Examples
Step
Seven
LOW LEVEL ALARM:
The goal is to make sure that an operator is notified if the liquid level falls below a certain point. If it does, an
alarm will sound, alerting the operator of a low level. A level switch must be mounted at the location where the
alarm will sound.
In this application, the level switch will be Wet all the time. When the level switch becomes Dry, the relay
contact will close causing the alarm to activate. Normal status for the application is for the controller to hold
the relay open with the alarm wired through the Normally Closed contact. The Relay will be energized, the
relay LED will be On and Invert will be Off. When the level switch becomes Dry, the relay will de-energize
causing the contact to close allowing the alarm to activate.
To do this, connect the hot lead of the alarm to the NC side of the relay terminal of the controller. If power is
lost, the relay will be de-energized, and the alarm will sound (if there is still power to the alarm circuit itself).
Note:
If power is accidentally cut to the controller, the level switch’s ability to notify the operator of a low level
alarm could be lost. To prevent this, the alarm circuit should have a non-interruptible power supply or some
other independent power source.
HIGH LEVEL ALARM:
In the same manor, this system can be used to sound an alarm when fluid reaches a high level, with just a
change in the location of the sensor and the setting of the Invert switch.
The alarm is still connected to the NC side of the relay to allow for a power failure alarm.
The sensor is normally dry. In this condition, we want the relay to be energized so the alarm does not sound:
i.e., the Red relay LED should be on whenever the Input LED is Amber. So we turn Invert On. If the fluid level
rises to the high sensor point, the sensor goes on, the relay de-energizes, and the alarm sounds.