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Introduction to Active Terminators for PROFIBUS DP

PROFIBUS operates at high frequencies (up to 12 Mbaud) using a physical copper transmission medium called RS485. For this reason, every PROFIBUS copper segment requires a terminating resistor at each end called a terminator. This terminator absorbs reflections of the signal where the copper cable segment ends. Reflections are bad news because they can corrupt PROFIBUS messages and cause network trips.
The termination is made up of a three resistor circuit of specially chosen resistors that match the impedance of the PROFIBUS cable.  For this circuit to work correctly, it needs to be powered with 5V which usually is supplied to the PROFIBUS Connector’s built –in terminator by the device it is connected to.


What happens if we lose power to the last device (by locking out the device) or we need to change it?  This is a problem because the last device is providing power to the termination which is preventing reflections from occurring on the PROFIBUS segment, now if we lose this termination, our entire network can be jeopardised! 
The solution is to insert the T1 PROFIBUS DP Active Terminator from PROFIBUS. Use of active terminators is considered best practice as they make your network more robust in the face of slave power failures, lock-outs of equipment or device maintenance. Losing one device will no longer affect the rest of your network.
 

Active PROFIBUS DP Terminator

   

"A redundant power supply and inspection port for PROFIBUS test equipment is what makes this PROFIBUS DP Active Terminator an outstanding option!"

The T1 Terminator provides active and reliable termination for PROFIBUS segments which are based on RS 485. By using this component it is possible to turn off, remove or replace devices without disturbing the bus communication.

The T1 has a couple of special features which makes it a very useful infrastructure component; a redundant power supply and diagnostic LEDs to indicate the status of each power source. It is also equipped with an additional DB9 connector for ProfiTrace or other maintenance/engineering tools. The DB9 connector can also be used as the primary bus connection if circumstances so dictate.

You'll often find the engineers from IDX carrying these in their toolboxes when doing PROFIBUS callouts. It is especially useful in the MCC environment where electricians lock out devices which at the last devices on the bus and are responsible for providing the bus termination. 

Adjustable PROFIBUS DP Active Termination

   

The T1-Pepper provides customizable (active) termination for PROFIBUS segments that do not comply with the standard RS 485 impedance. With rotary switches the impedance of the termination can be set. PROFIBUS networks exist that have not been wired with proper cable or where it is mandatory to use existing twisted pair cable. The T1-Pepper is an excellent solution to adapt the termination to the impedance of the cable. It can also be used to increase the idle line voltage on segments where interference causes communication disturbances and the large connectors allow specialty cable or more cable stress.

Applications:

  • PROFIBUS communication over non-standard cable.
  • Idle voltage increaser for EMC sensitive applications.
  • Impedance tuner for poor segments.

2 Rotary switches manipulate the values of the termination network. One for the middle resistor and one for the 2 pull-up resistors. The combination of both set the impedance and the level of the idle voltage. The T1-Pepper can be used by all fieldbuses that require active termination. It has a redundant power supply and diagnostic LEDs to indicate the status of each power source. 

COMbricks Adjustable PROFIBUS DP Active Terminator

   

The diagnostic alternative cable repeater (SALT) enables PROFIBUS communication over non-standard cable. Rotary switches allow setting the impedance. The user can verify the bus signals with the built in oscilloscope which is identical to the COMbricks SCOPE repeater module and accessible through the web server.

PROFIBUS networks that have not been wired with proper cable or where it is mandatory to use existing twisted pair cable are not uncommon. This product is an excellent tool to modulate PROFIBUS signals on non-standard infrastructures. It can also be used to increase the idle line voltage on segments where interference causes communication disturbances. The large connectors allow specialty cable and more cable stress.

Applications:

  • PROFIBUS communication over non-standard cable.
  • Idle voltage increaser for EMC sensitive applications.
  • Impedance tuner for poor segments.
  • Structures where large PROFIBUS connectors are required.

The repeater channel and the integrated oscilloscope are directly connected with the ProfiTrace OE core in the Head Station. Scope images and busmonitor data are directly available in the web server. The data traffic is constantly monitored for glitches which are digitally filtered out. It is able to drive 31 devices and has increased signal strength.

2 Rotary switches, one for the middle resistor and one for the 2 pull-up resistors, manipulate the values of the termination network. The combination of both set the impedance and the level of the idle voltage. At the other end of the cable another SALT repeater or the T1-PEPPER has to be placed (termination at both ends of the cable).