Unit 11 Float Switches Objectives

Unit 11 Float Switches Objectives

Unit 11 Float Switches Objectives

unit 11 float switches objectives

unit 11 float switches objectives

Unit 11
Float Switches
Objectives
After studying this unit , the student should be able to
• Describe the operation of float switches .
• List the sequence of operation for sump pumping or tank filling .
• Draw wiring symbols for float switches .
A float switch is used when a pump motor must
be started and stopped according to changes in
the water (or other liquid) level in a tank or
sump . Float switches are designed to provide
automatic control of AC and DC pump motor
magnetic starters and automatic direct control
of light motor loads .
The operation of a float switch is controlled by
the upward or downward movement of a float
placed in a water tank . The float movement
causes a rod-operated , Figure 11–1 , or chain and
counterweight , Figure 11–2 , assembly to open or
close electrical contacts . The float switch contacts
may be either normally open or normally closed
and may not be submerged . Float switches may
be connected to a pump motor for tank or sump
pumping operations or tank filling , depending
on the contact arrangement . See Figure 11–3 for
the elementary wiring circuits .
Electronic methods of control may be used in
place of the basic float switch for liquid level
control . These methods include electrode sensing ,
electronic wave transmission and detection ,
and other combinations .
Figure 11–4 shows a sump pump installation
with two float switches . Figure 11–5 is a control
circuit of the installed switches . The lower float
switch closes due to rising liquid . The sump continues
to fill until the upper float causes its
switch to close . When it closes , the pump motor
starts and closes maintaining contact “M , ” sealing
its circuit . The motor will pump out until the
lower float opens the circuit after emptying . This
arrangement extends the range of pumping .
An electrode , or stainless steel probe system
(Figure 11–6) , is similar to Figure 11–5 but
conducts a circuit in the liquid instead of using
floats . For satisfactory operation , the system
must be well grounded .

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