This document describes the operation of a floatless relay used to automatically control water levels. It contains diagrams and explanations of different models of floatless relays and their connections. The relays use electrodes at different water level points to control pumps for water supply and discharge operations. Alarms and indicator lights signal various water level conditions.

1. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
FLR501 A operation
Caution concerning electrode connection
●Check carefully the terminal symbols and electrode lengths before ●Use 0V to 100V terminal in the case of 100V AC power supply.
performing electrode circuit connection. ●Use 0V to 200V terminal in the case of 200V AC power supply.
E1 : upper limit, E2 : lower limit,
E3 : ground (be sure to ground E3)
Automatic water-supply operation
Power supply Operation
circuit breaker
Molded case
Electronic Power
relay
●The water-supply pump operates when water
circuit × surface leaves E2. (The water level is raised)
●The pump stops when water surface reaches E1.
●When turning on the power while the water sur-
face is within the control range (between E1 and
E2), the pump will not operate until the water
surface leaves E2.
Ground
Electromagnetic switch
Control
range
Water tank
Water supply source
Automatic water-discharge operation
Power supply Operation
circuit breaker
Molded case
Electronic Power
relay ●The water-supply pump operates when water
circuit ×
surface reaches E1. (The water level is lowered)
●The pump stops when water surface leaves E2.
Ground
Electromagnetic switch
Control
range
Water
tank
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2. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
FLR502 A operation
Caution concerning electrode connection
●Check carefully the terminal symbols and electrode lengths before ●Use 0V to 100V terminal in the case of 100V AC power supply.
performing electrode circuit connection. ●Use 0V to 200V terminal in the case of 200V AC power supply.
E1 : upper limit, E2 : lower limit,
E3 : ground (be sure to ground E3)
E4 : abnormal low-water supply alarm, E'1 : recovery, E'2 : lower limit
Automatic water-supply operation combined with pump idle prevention
Electronic Power Operation
relay
circuit ×1
Power supply Electronic Power Water tank
relay
circuit ●Water-supply pump operates when water surface
circuit breaker
×2
Molded case
leaves E2. (Water level is raised)
●The pump stops when water reaches E1.
●When turning on the power while the water sur-
face is within the control range (between E1 and
E2), the pump will not operate until the water
surface leaves E2.
Water supply source
Alarm buzzer ●The pump stops and the alarm sounds when
water surface leaves E'2.
Electromagnetic switch
Ground ●Normal water-supply operation resumes when
water surface reaches E'1.
Control ●Water-supply operation is performed normally
range when the water surface of the water supply source
Water tank
is between E'1 and E'2 while the power is on.
Water supply source
Automatic water-supply operation combined with abnormal low-water supply alarm
Electronic Power Operation
relay
circuit ×1
Power supply Electronic Power ●Water-supply pump operates when water surface
relay
circuit leaves E2. (Water level is raised)
circuit breaker
Molded case
×2
●The pump stops when water reaches E1.
●When turning on the power while the water sur-
face is within the control range (between E1 and
E2), the pump will not operate until the water
surface leaves E2.
●The pumps stops and the alarm sounds when
the water surface leaves E4 for some reason.
Alarm buzzer
Electromagnetic switch
Ground
Control
range
Water tank Low-water
supply
Water supply source
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3. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
FLR503 A operation
Caution concerning electrode connection
●Check carefully the terminal symbols and electrode lengths before ●Use 0V to 100V terminal in the case of 100V AC power supply.
performing electrode circuit connection. ●Use 0V to 200V terminal in the case of 200V AC power supply.
E1 : upper limit, E2 : lower limit,
E3 : ground (be sure to ground E3)
E4 : abnormal water increase alarm
Automatic water-discharge operation combined with abnormal water increase alarm
Electronic Power Operation
relay
circuit ×1
Power supply Power ●Water-discharge pump operates when water sur-
Electronic relay
circuit face reaches E1. (Water level is lowered)
circuit breaker
×2
Molded case
●The pump stops when water surface leaves E2.
●The pumps stops and the alarm sounds when
the water surface reaches E4 for some reason.
Alarm buzzer
Electromagnetic switch
Ground Abnormal water
increase
Control
range
Water tank
FLR505 A operation
LCD and alarm
Electronic Power Operation
relay
circuit ×1
Power supply
Electronic Power ●The upper limit lamp lights and the alarm sounds
relay
circuit ×2 when the water surface reaches E1.
circuit breaker
Molded case
●The middle lamp flashes when the water surface
is in the middle (between E1 and E2).
●The lower limit lamp lights and the alarm sounds
when the water surface leaves E2.
Upper limit lamp
Lower limit lamp
Alarm buzzer
Middle lamp
Ground
Upper limit
alarm
Middle
Water tank Lower limit
alarm
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4. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
FLR204 A operation
Caution concerning electrode connection
●Check carefully the terminal symbols and electrode lengths before ●Use B-C terminals instead of A-C terminals in the case of water-discharge operation.
performing electrode circuit connection. ●Use 0V to 100V terminal in the case of 100V AC power supply.
E1 : full tank alarm, E2 : upper limit, E3 : lower limit, E4 : low-water supply alarm ●Use 0V to 200V terminal in the case of 200V AC power supply.
E5 : Ground (be sure to ground E5 terminal)
Water-supply/water-discharge operation combined with full-tank/low-water supply alarm
Power
Electronic relay
circuit ×1
Power
Electronic relay
circuit ×2
Electronic Power
relay
circuit ×3
Power supply
circuit breaker
Molded case
Alarm buzzer
Full-tank lamp
supply lamp
Electromagnetic switch
Low-water
Ground
Full-tank
Control
range
Low-water
Water tank supply
Water supply source
Operation
Water-supply operation
●Water-supply pump operates when water surface leaves E3. (Water level is raised)
●The pump stops when water surface reaches E2.
●When turning on the power while the water surface is between E2 and E3, the pump will not operate until the water
surface leaves E3.
●Full-tank lamp lights and alarm sounds when water surface reaches E1 for some reason.
●Low-water supply lamp lights and alarm sounds when water surface leaves E4.
Water-discharge operation
●Discharge pump operates when water surface reaches E2. (Water level is lowered)
●The pump stops when water surface leaves E3.
●Full-tank lamp lights and alarm sounds when water surface reaches E1 for some reason.
●Low-water supply lamp lights and alarm sounds when water surface leaves E4.
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5. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
FLR206 A operation
Caution concerning electrode connection
●Check carefully the terminal symbols and electrode lengths before ●Use 0V to 100V terminal in the case of 100V AC power supply.
performing electrode circuit connection. ●Use 0V to 200V terminal in the case of 200V AC power supply.
Water supply source E1: upper limit alarm, E2: lower limit alarm recovery,
E3: lower limit alarm, E8: ground (be sure to ground E8 terminal)
Water tank E4: full-tank alarm, E5: upper limit, E6: lower limit,
E7: low-water supply alarm, E8: ground (be sure to ground E8 terminal)
Automatic water-supply operation with water-level display for water supply source
and water tank as well as pump idle prevention
Power
Electronic relay
circuit ×1
Power
Electronic relay
circuit ×2
Power
Electronic relay
circuit ×3
Power
Electronic relay
circuit ×4
Power
Electronic relay
circuit ×5
Power supply
circuit breaker
Molded case
Water tank low alarm
Water tank low lamp
Water supply source
Water tank full lamp
Water supply source
Water supply source
Water supply source
Water supply source
lower limit alarm
upper limit alarm
lower limit lamp
upper limit lamp
full alarm
Ground
Electromagnetic switch
Full-tank
Control
range
Water tank Low-water supply
Upper limit
Water supply source
Lower limit
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6. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
Operation
Water supply source
●Lower limit lamp lights, alarm sounds and pump stops when water surface leaves E3.
●Lower limit lamp and alarm turn off and pump can be prepared for operation when water surface reaches E2.
●Upper limit lamp lights and alarm sounds when water surface reaches E1.
Water tank
●Low-water supply lamp lights and alarm sounds when water surface leaves E7.
●Low-water supply lamp and alarm turn off when water surface reaches E7.
●Water-supply operates when water surface leaves E6. (Water level is raised)
●The pump stops when water surface reaches E5.
●Full tank lamp turns on and alarm sounds when water surface reaches E4 for some reason.
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7. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
51F-G B Operation
Caution concerning electrode connection
●Check carefully the terminal symbols and electrode lengths before ●Use 0V to 100V terminal in the case of 100V AC power supply.
performing electrode circuit connection. ●Use 0V to 200V terminal in the case of 200V AC power supply.
E1 : upper limit, E2 : lower limit,
E3 : ground (be sure to ground E3 terminal)
Automatic water-supply operation
Power supply Operation
circuit breaker
Molded case
Power
Electronic relay ●Water-supply pump operates when water surface
circuit ×
leaves E2. (Water level is raised)
●The pump stops when water reaches E1.
●When turning on the power while the water sur-
face is within the control range (between E1 and
E2), the pump will continue to operate until wa-
ter surface reaches E1.
Electromagnetic switch
Ground
Control
range
Water tank
Water supply source
Automatic water-supply operation
Power supply Operation
circuit breaker
Molded case
Electronic Power
relay ●Water-discharge pump operates when water sur-
circuit ×
face reaches E1. (Water level is lowered)
●The pump stops when water surface leaves E2.
Electromagnetic switch
Ground
Control
range
Water tank
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8. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
51F-G1 B operation
Caution concerning electrode connection
●Check carefully the terminal symbols and electrode lengths before ●Use 0V to 100V terminal in the case of 100V AC power supply.
performing electrode circuit connection. ●Use 0V to 200V terminal in the case of 200V AC power supply.
E1 : upper limit, E2 : lower limit,
E3 : ground (be sure to ground E3 terminal)
E4 : abnormal low-water supply alarm, E'1 : recovery, E2' : lower limit
Automatic water-supply operation combined with pump idle prevention
Power
Operation
Electronic relay
circuit ×1
Power supply Electronic Power Water tank
relay
●Water-supply pump operates when water surface
circuit breaker
circuit ×2
Molded case
leaves E2. (Water level is raised)
●The pump stops when water surface reaches E1.
Water supply source
●The pump stops and alarm sounds when water
surface leaves E'2.
●Normal water-supply operation resumes when
water surface reaches E'1.
Alarm buzzer ●Press the push-button to start pump in the case
Electromagnetic switch
water surface of water supply source does not
Push button reach E'1 during start or after recovering from
Ground
switch power failure.
Control range
●Do not press the push-button in the case low-
water supply alarm sounds and the pump stops
during normal operation.
Water tank
Water supply source
Automatic water-supply operation combined with abnormal low-water supply alarm
Power
Operation
Electronic
relay
circuit ×1
Power supply Electronic Power ●Water-supply pump operates when water surface
relay
circuit ×2 leaves E2. (Water level is raised)
circuit breaker
Molded case
●The pump stops when water surface reaches E1.
●The pump stops and alarm sounds when water
surface leaves E4 for some reason.
●Press the push-button to start pump in the case
water surface of water supply source does not
reach E4 during start or after recovering from
power failure.
●To stop the pump by releasing the push-button
Alarm buzzer switch, press and hold the push-button switch
until water surface reaches E4.
Electromagnetic switch
Push button
Ground switch
Control
range
Low-water supply
Water tank
Water supply source
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9. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
51F-G2 B operation
Caution concerning electrode connection
●Check carefully the terminal symbols and electrode lengths before ●Use 0V to 100V terminal in the case of 100V AC power supply.
performing electrode circuit connection. ●Use 0V to 200V terminal in the case of 200V AC power supply.
E1 : upper limit, E2 : lower limit,
E3 : ground (be sure to ground E3 terminal)
E4 : abnormal water increase alarm
Automatic water-discharge operation combined with abnormal water increase alarm
Electronic Power Operation
relay
circuit ×1
Power supply Electronic Power ●Water-discharge pump operates when water sur-
relay
circuit breaker
circuit ×2 face reaches E1. (Water level is lowered)
Molded case
●The pump stocks when water surface leaves E2.
●Alarm sounds when water surface reaches E4
for some reason.
Alarm buzzer
Electromagnetic switch
Ground Abnormal
water increase
Control
range
Water tank
51F-I B operation
LCD and alarm
Electronic Power Operation
relay
circuit ×1
Power supply Electronic Power ●Upper limit lamp lights and alarm sounds when
relay
circuit ×2 water surface reaches E1.
circuit breaker
Molded case
●Middle lamp lights when water surface is in the
middle (between E1 and E2).
●Lower limit lamp lights and alarm sounds when
water surface leaves E2.
Upper limit lamp
Lower limit lamp
Alarm buzzer
Ground
Middle lamp
Upper limit
alarm
Middle
Water tank
Lower limit
alarm
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10. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
FLRP301 (Compact Plug-In) A operation
Automatic standard water-supply or water-discharge operation
Power supply Operation
circuit breaker
Molded case
Water-supply operation
●Water-supply pump operates when water surface
Control
circuit leaves E2. (Water level is raised)
●The pump stops when water surface reaches E1.
●When turning on the power while the water sur-
face is between E1 and E2, the pump will not
Water Water operate until the water surface leaves E2.
discharge supply
Electromagnetic switch
Ground Water-discharge operation
●Water-discharge pump operates when water sur-
face reaches E1. (Water level is lowered)
Control
●The pump stops when water surface leaves E2.
range
Operation display Water-discharge opera-
Water tank tion
Water-supply operation
LED Pump Tank LED Pump Tank
Supplying Yellow OFF Normal
Water supply Yellow ON
water Discharging
source Red ON
Red OFF Normal water
※ For water-discharge operation, connect wire connected to
terminal 1 to terminal 11.
Automatic water-supply operation combined with pump idle prevention
Operation
Power supply Water tank
circuit breaker
●Water-supply pump operates when water surface
Molded case
leaves E2. (Water level is raised)
Control Control
circuit circuit ●The pump stops when water surface reaches E1.
●When turning on the power while the water sur-
face is within the control range (between E1 and
E2), the pump will not operate until the water
surface leaves E2.
Alarm buzzer
Water supply source
Electromagnetic switch
●The pump stops and alarm sounds when water
Ground
surface leaves E'2.
●Normal water-supply operation resumes when
Control water surface reaches E'1.
range
Operation display
Water tank
Water
P1LED P2LED Pump Tank supply Alarm buzzer
source
Yellow Yellow OFF Decrease Insufficient ON
Water supply source Yellow Red OFF Normal Insufficient ON
Supplying
Red Yellow ON water Normal OFF
Red Red OFF Normal Normal OFF
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11. Electronic Devices
Floatless Relay (Example of Connection)
Electronic Devices
51F-GPN (Compact Plug-In) B operation
Automatic standard water-supply or water-discharge operation
Power supply Operation
circuit breaker
Molded case
Water-supply operation
●Water-supply pump operates when water surface leaves
Control
circuit E2. (Water level is raised)
●The pump stops when water surface reaches E1.
●The pump operates when the power is turned on while
water surface is within the control range (between E1
Water Water and E2). The pump will not stop until water surface
discharge supply reaches E1.
Electromagnetic switch
Ground
Water-discharge operation
●Water-discharge pump operates when water surface
Control
reaches E1. (Water level is lowered)
range ●The pump stops when water surface leaves E2.
Water tank Operation display
Water-supply operation Water-discharge operation
LED Pump Tank LED Pump Tank
Water supply source Supplying Yellow OFF Normal
Yellow ON water
Discharging
Red OFF Normal Red ON water
※ For water-discharge operation, connect wire connected to
terminal 1 to terminal 11.
(long) (short) (middle) (long) (short) (middle)
Bottom
Bottom
Red view Red
view
Yellow Yellow
Electronic Electronic
circuit circuit
Yellow Yellow
Red Red
Water Water Water Water
supply discharge supply discharge
FLRP301 internal connection diagram 51F-GPN internal connection diagram
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