Endress+Hauser FTL31 Specifications

TI01147F/00/EN/03.16
71325891

Products Solutions Services

Technical Information

Liquiphant FTL31

Vibronic

Point level switch for liquids

Application

The Liquiphant FTL31 is a point level switch for liquids and is used in tanks, vessels
and pipes.

It is used for overfill prevention or pump protection in cleaning and filter systems as
well as in cooling and lubrication vessels, for instance.

Ideal for applications in which float switches or conductive, capacitance and optical
sensors have been used up to now. The Liquiphant FTL31 also works in areas where
these measuring principles are not suitable due to conductivity, buildup, turbulence,
flow conditions or air bubbles.

The Liquiphant FTL31 can be used for process temperatures up to:

• 100 °C (212 °F)

• 150 °C (302 °F)
Not suitable for hazardous areas.

The use of the Liquiphant FTL33 is recommended for hygiene areas.

Your benefits

• Operational safety, reliability and universal application thanks to the tuning fork
measuring principle

• Robust stainless steel housing (316L)

• External function test with test magnet

• Onsite function check possible thanks to LED indication

• Compact design for easy installation even in confined conditions or hard-to-access
areas

Table of contents

Liquiphant FTL31

Document information ....................... 3

Document conventions .......................... 3

Function and system design ................... 4

Measuring principle ............................ 4

Measuring system ............................. 4

Input ..................................... 5

Measured variable ............................. 5

Measuring range .............................. 5

Output ................................... 5

Switch output ................................ 5

Operating modes .............................. 5

Power supply .............................. 5

Supply voltage ............................... 5

Power consumption ............................ 5

Current consumption ........................... 5

Residual ripple ............................... 5

Electrical connection ........................... 5

Cable entry ................................. 9

Cable specification ............................ 10

Overvoltage protection ......................... 10

Performance characteristics .................. 11

Reference operating conditions ................... 11

Switch point ................................ 11

Hysteresis ................................. 11

Non-repeatability ............................ 11

Influence of ambient temperature ................. 11

Influence of medium temperature .................. 11

Influence of medium pressure .................... 11

Switching delay .............................. 11

Switch-on delay ............................. 11

Measuring frequency .......................... 11

Measured error .............................. 11

Process .................................. 17

Process temperature range ...................... 17

Process pressure range ......................... 17

Density ................................... 17

State of aggregation ........................... 17

Viscosity .................................. 17

Solids contents .............................. 17

Lateral loading capacity ........................ 17

Mechanical construction .................... 18

Design .................................... 18

Connector ................................. 19

Tuning fork ................................ 19

Sensor type ................................ 20

Weight ................................... 23

Materials .................................. 23

Surface roughness ............................ 24

Operability ............................... 25

LED display ................................ 25

Function test with test magnet .................... 25

Certificates and approvals ................... 26

CE mark ................................... 26

EAC conformity .............................. 26

RCM-Tick marking ............................ 26

Approval .................................. 26

Overfill prevention ............................ 26

Marine approvals ............................ 26

CRN approval ............................... 26

Inspection certificates .......................... 26

Manufacturer declarations ...................... 26

Pressure Equipment Directive .................... 26

Other standards and guidelines ................... 26

Ordering information ...................... 27

Ordering information .......................... 27

Services (optional) ............................ 27

Installation ............................... 12

Orientation ................................ 12

Installation instructions ........................ 12

Length of connecting cable ...................... 14

Environment .............................. 15

Ambient temperature range ..................... 15

Storage temperature .......................... 15

Climate class ............................... 15

Altitude ................................... 15

Degree of protection .......................... 16

Shock resistance ............................. 16

Vibration resistance ........................... 16

Electromagnetic compatibility .................... 16

Reverse polarity protection ...................... 16

Short-circuit protection ........................ 16

Accessories ............................... 27

Weld-in adapter ............................. 27

Plug-in jack, cable ............................ 27

Additional accessories ......................... 28

Supplementary documentation ............... 29

Operating Instructions ......................... 29

Additional documentation ...................... 29

Certificates ................................. 29

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Liquiphant FTL31

DANGER

WARNING

CAUTION

NOTICE

Document information

Document conventions Safety symbols

Symbol Meaning

Electrical symbols

A0011189-EN

A0011190-EN

A0011191-EN

A0011192-EN

DANGER!

This symbol alerts you to a dangerous situation. Failure to avoid this situation
will result in serious or fatal injury.

WARNING!

This symbol alerts you to a dangerous situation. Failure to avoid this situation
can result in serious or fatal injury.

CAUTION!

This symbol alerts you to a dangerous situation. Failure to avoid this situation
can result in minor or medium injury.

NOTE!

This symbol contains information on procedures and other facts which do not
result in personal injury.

Symbol Meaning

Ground connection

A grounded terminal which, as far as the operator is concerned, is grounded via a grounding

A0011200

system.

Protective ground connection

A terminal which must be connected to ground prior to establishing any other connections.

A0011199

Symbols for certain types of information

Symbol Meaning

Permitted

Indicates procedures, processes or actions that are permitted.

A0011182

Forbidden

Indicates procedures, processes or actions that are forbidden.

A0011184

Tip

Indicates additional information.

A0011193

Reference to documentation

Refers to the corresponding device documentation.

A0011194

Reference to page

Refers to the corresponding page number.

A0011195

Symbols in graphics

Symbol Meaning

1, 2, 3 ... Item numbers

A, B, C, ... Views

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Function and system design

2

1

3

Liquiphant FTL31

Measuring principle

Measuring system

A piezoelectric drive causes the tuning fork of the Liquiphant FTL31 to vibrate at its resonance
frequency. When the tuning fork is immersed in a liquid, its intrinsic frequency changes due to the
change in density of the surrounding medium. The electronics system in the point level switch
monitors the resonance frequency and indicates whether the tuning fork is vibrating in air or is
covered by liquid.

A signal is output via the DC-PNP or AC/DC electrical connection.

The measuring system consists of a Liquiphant FTL31 point level switch, e.g. for connection to
programmable logic controllers (PLC), a mini-contactor or solenoid valve.

1 Overfill prevention or upper level detection MAX (maximum safety)
2 Lower level detection MIN (minimum safety)
3 Lower level detection MIN, e.g. dry running protection for pump

A0020911

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Liquiphant FTL31

Input

Measured variable

Measuring range

Switch output

Operating modes

Density

> 0.7 g/cm³ (optionally available: > 0.5 g/cm³)

Output

Switching behavior: On/Off

Function

3-wire DC-PNP:
Positive voltage signal at the switch output of the electronics (PNP), switching capacity 200 mA
2-wire AC/DC:
Load switching in the power supply line, switching capacity 250 mA

The device has two operating modes: maximum safety (MAX) and minimum safety (MIN).

By choosing the corresponding operating mode, the user ensures that the device also switches in a
safety-oriented manner even in an alarm condition, e.g. if the power supply line is disconnected.

• Maximum safety (MAX)
The device keeps the electronic switch closed as long as the liquid level is below the fork. Sample
application: overfill prevention

• Minimum safety (MIN)
The device keeps the electronic switch closed as long as the fork is immersed in liquid. Sample
application: Dry running protection for pumps

The electronic switch opens if the limit is reached, if a fault occurs or the power fails (quiescent
current principle).

Supply voltage

Power consumption

Current consumption

Residual ripple

Electrical connection

Power supply

DC-PNP:
AC/DC:

DC-PNP:
AC/DC:

DC-PNP:
AC/DC:

DC-PNP:
AC/DC:

Two electronic versions and three different connections are available for the device.

• Electronic version 3-wire DC-PNP with connection; M12 plug, valve plug or cable

• Electronic version 2-wire AC/DC with connection; valve plug or cable

A fine-wire fuse is necessary for operation: 500 mA slow-blow.

Electronic version 3-wire DC-PNP

3-wire DC-PNP is preferably used in conjunction with programmable logic controllers (PLC), DI
modules as per EN 61131-2. Positive signal at the switch output of the electronics (PNP).

Voltage source: non-hazardous contact voltage or Class 2 circuit (North America).

10 to 30 V DC, 3-wire
20 to 253 V AC/DC, 2-wire

< 975 mW
< 850 mW

< 15 mA
< 3.8 mA

5 Vss 0 to 400 Hz
—

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Liquiphant FTL31

0.5A

L– L+

2

1

3

4

K

0.5A

L–

L+

2

1

3

4

K

1

21

2

1

41

4

0.5A

L– L+

2

1

3

4

K1

K2

1

2

1

4

4

1

1 2

21

41

Connection with M12 plug

Depending on the analysis of the switch outputs, the device works in the MAX (maximum safety) or
MIN (minimum safety) mode.

A cable is optionally available for order, see "Accessories" section →  27.

3-wire DC-PNP Operating mode

M12 connector MAX MIN

A0022901

SymbolsKDescription

Yellow LED (ye) lit
Yellow LED (ye) not lit
external load

Function monitoring with M12 connector

Using a two-channel analysis, function monitoring of the sensor can be implemented in addition to
level monitoring, e.g. per relay switch, PLC, AS-i Bus I/O module, …).

When both outputs are connected, the MIN and MAX outputs assume opposite states when the
device is operating fault-free (XOR). In the event of an alarm condition or a line break, both outputs
are deenergized.

Connection with 3-wire DC-PNP for function monitoring based on XOR logic

Sensor covered

Sensor exposed

Fault

A0022917

Symbols

K1 / K2

Description

LED lit
LED not lit
Fault or warning
external load

Yellow LED

(ye)

Red LED

(rd)

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Liquiphant FTL31

1

3

0.5A

L–

L+

2

K

+

–

L–

L+

3

0.5A

1

2

K

+

–

3

23

2

2323

0.5A

1

2

3

L–

L+

K

+

L+

0.5A

K

1

2

3

L–

+

3

23

2

2323

Connection with valve plug or cable

Depending on the assignment of the connector or the wiring of the cable, the device works in either
the MAX or MIN operating mode.

3-wire DC-PNP Operating mode

Valve plug MAX MIN

A0022900

Cable (cannot be
dismantled)

Core colors:
1 = BK (black)
2 = GR (gray)
3 = BN (brown)
Ground = GNYE (green­yellow)

SymbolsKDescription

Yellow LED (ye) lit
Yellow LED (ye) not lit
external load

A0022902

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Liquiphant FTL31

2.7

2.5

2.3

2.1

1.9

1.7

1.5

1.3

1.1

0.9

0.7

0.5
20 24 27 43 48 53 60 110 121 207 230 253

P/S

U

P1

P2

Electronic version 2-wire AC/DC

The load is switched via an electronic switch directly in the power supply circuit. Always connect in
series with a load!

Not suitable for connection to low-voltage PLC inputs!

Selection tool for relays

 1 Minimum rated power of the load

P/S Rated power in [W] / [VA]
U Operating voltage in [V]

Item Supply voltage

P1
AC mode

P2
DC mode

24 V
110 V
230 V

24 V

48 V

60 V

min max

> 1.3 VA
> 1.5 VA
> 2.5 VA

> 0.7 W
> 0.9 W
> 1.5 W

Rated power

< 6 VA
< 27.5 VA
< 57.5 VA

< 6 W
< 12 W
< 15 W

Relays with a lower rated power can be operated by means of an RC module connected in parallel
(optional).

A0023486

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Liquiphant FTL31

3

0.5A

1

K

>20 V

L1/L+ N/L–

2

0.5A

1

K

>20 V

L1/L+ N/L–

1313

1

21

2

3

L1/L+

0.5A

K

>20 V

1

2

N/L–

1

L1/L+

0.5A

K

2

3

N/L–

>20 V

1313

1

21

2

A

B

C

Connection with valve plug or cable

Depending on the assignment of the connector or the wiring of the cable, the device works in either
the MAX or MIN operating mode.

When the cable is wired, one wire of the cable does not have any function in each of the operating
modes (brown in the case of MIN, and gray in the case of MAX). The cable with no function must be
secured against inadvertent contact.

2-wire AC/DC Operating mode

Valve plug MAX MIN

Cable entry

Cable (cannot be dismantled)

Core colors:
1 = BK (black)
2 = GR (gray)
3 = BN (brown)
Ground = GNYE (green-yellow)

SymbolsKDescription

Yellow LED (ye) lit
Yellow LED (ye) not lit
external load

A0022900

A0022902

A0021219

A0021418

A0022161

A0021418

A0021220

A0021420

A0022225

A0021420

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A0020928

A Valve plug (M16x1.5; NPT ½"; QUICKON)
B M12 connector
C Cable 5 m (16 ft); secured in place on delivery and cannot be disassembled

Liquiphant FTL31

Cable specification

Overvoltage protection

• Valve plug
– Cable cross-section: max. 1.5 mm2 (AWG 16)
– Ø 3.5 to 8 mm (0.14 to 0.26 in)

• M12 connector: IEC 60947-5-2

• Cable (3LPE)
– Cable cross-section: 0.75 mm2 (AWG 20)
– Ø 6 to 8 mm (0.24 to 0.31 in)
– Material: PUR

Overvoltage category II

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