Series 195 Profibus Explained: GSD Configuration and Diagnostics in Practice

Series 195 is Germanjet’s Profibus DP fieldbus magnetostrictive displacement sensor. Profibus DP is based on an RS-485 physical layer, uses master–slave polling, and relies on a GSD file for device configuration. Its practical value is concentrated on existing production lines: a large installed base of Siemens S7-300/400 systems uses Profibus as the backbone, so adding or replacing a position sensor on Profibus avoids rebuilding the master and the network. Measuring performance matches the rest of the range — absolute position output, resolution steps 1–100 μm, repeatability of the order of ±0.002 mm.

The GSD file: starting point of configuration

GSD (General Station Description) is the slave’s electronic datasheet. It tells the master which baud rates, diagnostic capabilities, available modules and parameter structures the device supports. Without the correct GSD the master cannot complete configuration, appearing as “the device is on the network but configuration reports an error”.

Three practical points:

• Version must match firmware. If the GSD is older than the device firmware, some parameters or diagnostic items cannot be configured; if it is newer, the master may request functions the device does not support.
• Rescan the hardware catalogue after installation. After the configuration software imports the GSD, refresh the catalogue, or the new device will not appear in the selectable list.
• Module selection must match the actual need. Position-value data length (byte count) and whether a speed value is attached are both decided at module selection; a wrong choice misaligns the data that are read.

The full Profibus configuration flow is in Profibus DP introduction: GSD files and configuration.

Slave address and baud rate

Two basic Profibus DP settings:

Slave address is unique on the same segment, set by a DIP switch on the device or in software. An address clash causes two devices to answer at once; on the master the station repeatedly comes online and drops out.

Baud rate is decided by the master; slaves usually auto-detect. As with CAN, the higher the baud rate, the shorter the allowed segment length — a physical constraint of RS-485 transmission. If long distance is needed on site, lower the baud rate deliberately rather than forcing a high rate, or the error rate will fluctuate with temperature and interference — intermittent faults of the “fine by day, drops out at night” kind are extremely costly to find.

Terminating resistors and bus topology

Profibus uses dedicated bus plugs with an integrated terminating-resistor switch. Rules:

• Set the plugs of the devices at both ends of the segment to ON; set all middle devices to OFF;
• The terminating resistor needs power to work — fitting a terminated plug on a de-energised device makes the match fail; this is an easily missed detail;
• Unplugging a middle device should not break the bus (dedicated plugs are designed as a through structure), but unplugging an end plug loses matching for the whole segment.

Topology must be linear; spurs should be avoided as far as possible at high baud rate. The physical mechanism of terminating resistors is the same as CAN; see Terminating resistors and bus length. Profibus-specific diagnostic methods are in Profibus diagnostics and terminating resistors in practice.

Diagnostic capability: the practical Profibus advantage

The standard Profibus DP diagnostic mechanism is much stronger than analog and SSI. The master can read the slave’s diagnostic telegram and distinguish “device not responding”, “parameter error”, “configuration mismatch”, “internal device fault” and other states. On a multi-station line this shortens location time significantly — there is no need to strip stations one by one; look at the diagnostic information first to locate the station number and fault class.

The engineering recommendation is to map the diagnostic word into a PLC data block and display it on the HMI, rather than only opening the programming software online when a fault occurs. Common position-sensor failure modes and the troubleshooting order are in Common fault finding; dedicated investigation of lost fieldbus data is in Lost fieldbus data: terminating resistor / address clash / water ingress.

Series 195 versus other fieldbus types

Dimension	Profibus DP (195)	CANopen (194)	PROFINET (199PROFINET)	EtherCAT (197)
Physical layer	RS-485 twisted pair	CAN differential twisted pair	Ethernet	Ethernet
Configuration file	GSD	EDS	GSDML	ESI (XML)
Communication mechanism	Master–slave polling	Multi-master / producer–consumer	Real-time Ethernet, IRT supported	Processing-frame on-the-fly, DC synchronisation
Terminating resistor	Built into the plug, ON at both ends	120 Ω at each end	Not required	Not required
Diagnostics	Standard diagnostic telegram, mature	EMCY emergency message	Rich diagnostics, topology identification supported	Slave state machine + error counters
Main application	Existing S7-300/400 lines	Mobile machinery, multi-axis hydraulics	New Siemens-system lines	High-speed multi-axis synchronisation
Reason to choose	Compatible with the existing network, low conversion cost	Low cost, mature ecosystem	Fusion with the upper IT network	Strongest real-time performance

Conclusion: new projects generally will not choose Profibus of their own accord, but on existing-plant conversion it is often the lowest-cost choice. The criterion is the master and the existing network, not how advanced the protocol itself is. The full trade-off among the four fieldbuses is in Comparing the whole fieldbus range.

Selection and deployment advice

Typical conditions for choosing the Series 195 Profibus: the master is a Profibus DP master; a Profibus backbone already exists on site with spare stations; the conversion window is short and the control system must not be changed.

If the line is migrating to an Ethernet system, evaluate 199PROFINET (smooth upgrade in the Siemens system; see 199PROFINET explained) or Series 197 EtherCAT (high-speed synchronisation; see Series 197 EtherCAT explained). If it is only a single-axis reading and fieldbus is not needed, Series 192 SSI or Series 191 analog is simpler; the comparison is in Analog vs. digital across the whole range. General fieldbus wiring points are in Fieldbus practical guide.