Industrial Automation

Terminating Resistors for PROFIBUS networks

Correct termination of a PROFIBUS segment

PROFIBUS Terminating Resistors with M12 Connector

Passive M12 terminating resistors are installed on the output port of the final PROFIBUS station when it does not have its own integrated terminator. Correct segment termination reduces signal reflections and helps maintain stable communication, especially at higher transmission speeds.

  • B-coded M12
  • Male and female versions
  • Compact industrial design
  • Simple screw-on installation
  • Products in stock at FOXON
Discuss network termination View the T1 active terminator
Termination must be enabled at both physical ends of the segment
ON1
2
3
ON4
Exactly two active terminations
F M12 female – code 22261001

For a male M12 end port. Version for PROFIBUS, DeviceNet and CANopen.

M M12 male – code 22260722

For a female M12 end port. Compact terminator designed for PROFIBUS DP.

How do you select and connect a PROFIBUS terminating resistor correctly?

Select the connector according to the final station port

M12 female

Terminating Resistor for PROFIBUS, DeviceNet and CANopen

LAPP 22261001

Terminating resistor with a female M12 connector for screwing onto a male M12 output port.

  • female M12 version,
  • five contacts,
  • shielded design,
  • for PROFIBUS, DeviceNet and CANopen,
  • compact and robust construction.
M12 male

Terminating Resistor for PROFIBUS DP

LAPP 22260722

Terminating resistor with a male M12 connector for screwing into a female M12 output port.

  • male M12 version,
  • four contacts,
  • B coding for PROFIBUS,
  • compact dimensions,
  • robust industrial design.
1 Find the physical ends of the segment

Termination belongs at the first and final electrical points of the segment, not automatically at the devices with the lowest and highest addresses.

2 Select the opposite connector version

A male M12 port requires a female terminator. A female M12 port requires a male terminator.

3 Check the power supply of the final station

The passive termination network must be powered correctly by the end device. Switching off the station can therefore affect segment termination.

Termination in a DB9 connector

On standard PROFIBUS connectors, the resistor is enabled by moving the switch to ON. On stations inside the segment, it must remain OFF.

View PROFIBUS connectors
Separate M12 resistor

Used mainly on devices with M12 ports that do not have an integrated switchable terminator. The resistor is screwed onto the M12 output of the first and final stations.

T1 active terminator

Another option is the T1 active terminator. It has its own power supply and keeps the segment terminated even when the final station is switched off, disconnected or replaced.

View active termination

Basic PROFIBUS termination rules

Every electrical segment must have two terminations
Termination must be at the physical ends of the cable
Resistors inside the segment must remain switched off
Do not add a third terminating resistor
Verify the power supply of both end terminations
Measure the segment with ProfiTrace 2 after modification
Check the correct connection of conductors A and B
Observe the maximum length for the selected speed
Minimise long and unnecessary stubs

Most common PROFIBUS termination mistakes

  • only one terminating resistor is enabled,
  • three or more resistors are enabled in one segment,
  • a resistor is enabled on a station in the middle of the cable route,
  • the final station supplying the termination is switched off,
  • a terminator with the wrong connector version is used,
  • the physical end of the segment is confused with the highest device address,
  • the termination switch in an old connector is defective.
How does a termination fault appear?

The network may suffer random outages, telegram retries, diagnostic alarms or problems that occur only at higher speed, with a longer cable or when the machine’s power section starts.

How can termination be verified?

The ProfiTrace 2 tester displays signal quality and the oscilloscope waveform. An experienced technician can identify missing, excessive or incorrectly powered termination.

Not sure where the resistor should be installed?
Send us a simple diagram of the cable route, photographs of the first and final devices, connector types and the transmission speed. We will help determine the physical ends of the segment and select the correct M12 terminator version.
Active PROFIBUS termination PROFIBUS connectors PROFIBUS cables ProfiTrace 2 PROFIBUS tester PROFIBUS network diagnostics and repairs Practical PROFIBUS network training Complete range for PROFIBUS networks
PROFIBUS: 3 Sins and 10 Tips

PROFIBUS: 3 Sins and 10 Tips

The PROFIBUS industrial bus is highly tolerant and will forgive many faults. But if a critical fault occurs—or several small ones accumulate—you will definitely notice. That’s why this aging industrial network deserves attention. Even if faults on your network are still rare, they will gradually accumulate. What do our technicians recommend? What are their 10 tips for maintaining PROFIBUS?

Question or Inquiry

Are you looking for a spare part, a repair, one of our products, or do you need to check availability or get advice on a technical solution? Send us the order number, a photo of the nameplate, or a brief description of your request. We will usually get back to you within one hour during business hours.

Highlighted items are mandatory.