MN301535 Rev A
15
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Application Examples
Step
Seven
PUMP PROTECTION:
The key here is to install a level switch just above the outlet to the
pump. As long as the switch is Wet, the pump can operate. If the
switch ever becomes Dry, the relay will open preventing the pump
from running. To prevent relay chatter, add a small relay delay.
Note:
In this application, the relay to the
pump must be closed while the level
switch is Wet. To do this, connect the
relay through the NO side of the relay and
set Invert to the OFF position. If power is
lost to the controller, the relay will de-
energize and keep the circuit open
preventing the pump from running.
AUTOMATIC FILL:
This system consists of a tank with a high level sensor, a low level sensor,
and a valve that is controlled by the controller.
Part of a proper fail-safe design for this
particular system is that if power is lost to the
controller for any reason, the valve filling the
tank must be closed. Therefore, we connect
the valve to the NO side of the relay. When
the relay is energized, the valve will open and
fill the tank. In this case, Invert should be ON.
The relay indicator will correspond directly to
the open/close status of the valve.
Determining the settings of LATCH and INVERT:
This is the way the
system must operate:
When both the high and low sensors are dry, the valve will open
(relay energized), starting to fill the tank.
When the low sensor gets wet, the valve will remain open (relay
energized).
When the high sensor gets wet, the valve will close (relay de-
energized.
When the high sensor becomes dry, the valve will remain closed
(relay de-energized).
Latch:
In any two-sensor control system, LATCH must be ON.
Invert:
Referring to the logic chart in Step Eight, we look for the setting that will de-energize the relay (start the
pump) when both inputs are wet (Amber LEDs). In this system, Invert should be ON.
Determining A or B input connections:
When LATCH is ON, there is no effective difference between Input
A and B, since both sensors must have the same signal in order for status to change. When wiring any two-
input relay section, the only consideration for hooking a particular sensor to A or B is if LATCH will be OFF.