Page 56 MSI-3750CS RF Weighmeter • User Guide
3750CS
C
ELL
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CALE RF DIGITAL WEIGHT INDICATOR
®
Relay Applications
Some examples of uses for the set point relays are: Using the normally open position of a set point as a switch to
turn on a light or siren when the set point is reached, using the normally closed position to cut out a motor when
a set point is reached, or using the set point relays to change speeds on a motor. See figure 1 for an example hook
up to a lamp. The normally open (NO) contact of a relay is used to turn devices on when a set point is reached,
while the normally closed (NC) contact is used to turn a device off when the set point is reached. The common
(COM) contact connects the power to the relay.
Figure 1
Set Points are often used in conjunction with automatic conveyer belts. By using the set point relays conveyor
belts can be controlled by weight. Using two Set Points allows speed control for dribbling or speeding up,
etc. Figure 2 shows a simple arrangement where the motor is turned off when a set point is reached. Pay
attention to the current and voltage ratings of the relay when using them for motor control. It may be necessary
to use a boost relay externally as in figure 3.
Figure 2
Figure 3
By combining the relay outputs of 2 or more set points, complex conditional logic functions can be achieved. In
figure 4, two set point outputs are combined to control a motor when the conditions for both set points are true.
In figure 5 two relays are combined to turn on a motor when either Set Point is true. One major application for
combining relays is to use one for a master start/stop for all the other relays.
