Скачать или смотреть Profibus OLM configuration -The Secret to PROFIBUS Success: Why Termination is EVERYTHING

PROFIBUS networks require precise configuration for reliable signal transmission, especially concerning bus termination.

I this video you may discover The Secret to PROFIBUS Success: Why Termination is EVERYTHING

OLM and Connector Switch Position
When a PROFIBUS connector plugs into an OLM's electrical D-sub port, its termination switch must be "ON" if the OLM marks the beginning or end of an electrical segment. This is because bus termination is crucial for preventing signal reflections, which cause data corruption and network malfunction. The termination circuit, an active bus terminator, typically consists of three resistors. The termination is only needed at the two physical ends of any given PROFIBUS segment. For intermediate nodes, the connector's termination switch should be "OFF" to avoid signal issues.
Chapters:
00:00 – Introduction: Fiber-to-Copper Profibus Termination
00:16 – About Technical University & Training Programs
00:33 – The Scenario: OLM to Two VFDs
00:47 – Core Principle: Active Termination Explained
01:04 – Why Termination is Needed (Signal Reflection)
01:20 – Inside a Profibus Connector: Resistor Network
01:48 – Two Key Jobs of Active Termination (Impedance & Bias)
02:19 – The Rule: First and Last ON, Middle Devices OFF
02:51 – Applying the Rule to OLM, VFD1, and VFD2
03:07 – OLM as First Node → Termination ON
03:24 – VFD #1 as Intermediate Node → Termination OFF
04:14 – VFD #2 as Last Node → Termination ON
04:50 – Simple Checklist: ON, OFF, ON

05:09 – Key Takeaways: Active Termination is Mandatory
05:23 – Misconfigured Switches = Unstable Networks
05:51 – Bigger Picture: Impact of One Wrong Termination

06:09 – Common Problem: Last Device Has No Connector
06:22 – Problem Setup (OLM → VFD1 → VFD2 without DB9)
06:51 – Why Termination Is Non-Negotiable (IEC Standard)
07:38 – Active Terminator Circuit Details (Resistors & 5V)
08:13 – Electrical Roles: Kill Reflections & Idle Voltage

08:42 – Solution A: Internal VFD Termination (Check Manual)
09:29 – Solution B: External Connector with Terminator
10:01 – How to Wire & Enable External Termination

10:17 – Danger of Double Termination Explained
10:46 – Why Two Terminators in Parallel Break the Standard
11:03 – How Double Termination Overloads Line Drivers

11:33 – The Four Laws of Profibus Termination
11:50 – Rule 1: First Node ON
11:50 – Rule 2: Last Node ON
11:50 – Rule 3: Middle Nodes OFF
11:50 – Rule 4: Exactly Two Terminators Per Segment
12:07 – Golden Rule: Always Check the Device Manual

12:23 – Final Thoughts: Reliability Beyond “It Works”

OLM and Termination Rules
An Optical Link Module (OLM) acts as a gateway between fiber and copper-based PROFIBUS segments. Its electrical (copper) side requires proper termination.

Principle: Bus termination is critical for preventing signal reflections on the PROFIBUS RS-485 bus. Reflections occur when signals reach the end of the cable and bounce back, corrupting data.

Active Terminator: A PROFIBUS terminator is a simple three-resistor circuit. It absorbs the signal at the end of the line and provides a DC bias to the cable.

The Rule of Two: Every electrical PROFIBUS segment must have exactly two active terminators: one at the first device and one at the last device. All intermediate devices must have their termination disabled.

A VFD Daisy-Chain Scenario
Consider a network with an OLM connected to two daisy-chained Variable Frequency Drives (VFDs) where the last VFD lacks a standard 9-pin connector.

OLM (First Node): The PROFIBUS connector on the OLM's electrical port must have its termination switch set to "ON" because it marks the start of the copper segment.

First VFD (Intermediate Node): This device is in the middle of the segment, so its internal or external termination must be set to "OFF".

Last VFD (Last Node): As the physical end of the segment, this device needs a terminator. Since it lacks a standard connector, a separate, external active bus terminator must be manually wired to its terminals.

Common Issues and Solutions
Double Termination: A common mistake is having a device with internal termination enabled while also using an external connector with its termination switch set to "ON." This "double termination" overloads the line drivers and causes severe signal degradation, leading to network communication failures.

The Four Laws:

The first node must have its termination ON.
The last node must have its termination ON.
All middle nodes must have termination OFF.
A segment must have exactly two terminators.

Final Advice: Always consult the device manual to understand its specific termination capabilities. Trusting a network because it "works" temporarily is risky; proper termination is essential for long-term reliability.