WITT FSMP system – reliably measuring and documenting driving voltage over long periods

Name: Traction Voltage Monitoring – WB-FSMP: Flexible and Reliable
Brand: WITT Bridge

How the WITT FSMP system can be used to record track voltage continuously over weeks and months – either as a cabinet mounted directly on the mast or as a simple measurement setup in the points cabinet, with buffered auxiliary power, configurable monitoring thresholds and remote transmission of measurement data.

Documenting Traction Voltage or power quality

Whether the Traction Voltage actually remains within the expected range can only be reliably assessed through continuous, long-term measurement – a one-off test is not sufficient for this purpose. The WITT FSMP system is designed precisely for this purpose: a measurement and documentation platform configured using WITT Bridge components, which automatically and continuously records Traction Voltage at a sampling rate of up to 1 kHz, automatically switches to battery power in the event of a mains failure, and both stores the measurement data locally and, optionally, transmits it via mobile network. In addition, monitoring thresholds can be freely configured so that the system issues automatic warnings when necessary – for example, if the Traction Voltage falls below a critical value. The system can be operated either as a cabinet mounted on the mast with a direct Traction Voltage supply, or as a simple measurement setup in the points cabinet using a 24 V DC auxiliary voltage.

The task

Automatically and continuously record the Traction Voltage, defined as 750 V DC +10 per cent, over a long period of time and document the actual voltage, rather than carrying out manual individual measurements
Provide a measurement range that extends well beyond the normal tolerance band (400–1,000 V DC) in order to reliably detect even atypical or critical voltage conditions
Configurable monitoring thresholds allow a notification to be triggered automatically if these thresholds are exceeded or not met (for example: a voltage below 500 V DC triggers a notification via email, SMS or via WB-DO 4)
To provide a flexible measurement platform that can be operated, depending on the location, either directly from the Traction Voltage or railway power (cabinet on the mast) or via a 24 V DC auxiliary power supply (e.g. in a switch cabinet on site)
To allow for an adjustable recording frequency between 20 Hz and 1 kHz, so that a balance can be struck between data volume and level of detail, depending on the specific requirements
To continue recording measurement data reliably even in the event of a loss of auxiliary power, and to shut down the system in a controlled and traceable manner
To be able to document data both locally and transmit it over the air, with critical conditions escalated via SMS
To provide an easy-to-use interface that does not require internet access

WITT FSMP System Project Description

The WITT FSMP system starts up automatically as soon as the auxiliary power supply is connected; it first checks that all components are communicating with one another and, if the check is successful, automatically switches to measurement data recording mode. The system’s internal web interface can be accessed from this point onwards – no internet connection is required.

The WB-PSU forms the input stage: it withstands a traction voltage of up to 800 V DC during normal operation and up to 1,500 V DC for short periods; it is therefore protected by a 1,500 V DC fuse and features Class 2 overvoltage protection as well as an input-side interference filter – necessary to shield the downstream measurement equipment from the severe interference and overvoltages typical in traction power systems, such as those caused by lightning strikes.

The WB-AP ensures an uninterrupted power supply: it bridges voltage dips in the 24 V DC auxiliary voltage, is electrically isolated between the input (IN) and the auxiliary voltage (OUT) supplied to the measurement platform, and thus forms the basis for interference-free measurement data acquisition. If no input voltage is present, the built-in battery takes over the power supply for at least three hours (optionally longer); if the battery level drops too low during this time, the system reports this as an event, shuts down automatically in an orderly manner and restarts automatically as soon as the auxiliary voltage is restored.

The actual voltage measurement is carried out by the WB-AI 1-channel module (AI = Analogue Input): Within the qualified measurement range of 400 to 1,000 V DC (± 5 V DC), it records at a standard sampling rate of 1 kHz – adjustable in 10-Hz increments between 10 Hz and 1 kHz – with a data resolution of 12 bits. This measurement range is deliberately set significantly wider than the tolerance band of the rated voltage (750 V DC +10 %), so that even exceptional operating conditions are reliably documented as the actual voltage. If the voltage lies outside the qualified range – below 400 V DC or above 1,000 V DC – the system signals this and does not store any measurement data within this range. The module is calibrated using WITT measurement standards.

Threshold values for the monitoring process itself can be freely configured: the WB-DO 4 provides four dry contacts for this purpose, which signal configurable threshold values (in 10 V increments) as well as when these values are exceeded or not reached. For example, a threshold of 500 V DC can be set; if the value falls below this threshold, a notification is automatically triggered – either by email or via the WB-DO 4’s potential-free contact – without the need for constant manual monitoring of the measured values.

Measurement data storage is managed via the WB-HS, an industrial embedded system running Linux, which also provides the local web interface for configuration and operation – without the need for internet access. If remote transmission is required, the WB-OtA G4 is used: it temporarily stores the data on the WB-HS and transmits it via LTE to a data sink, provides the system time and also reports the operating status via text message or email – the SIM card required for this is not supplied.

Mechanically, the measurement setup is mounted on two mounting plates, which are secured to the housing mounting plate with screws and installed within the GRP cabinet. The WB-PSU, including the fuse system, sits directly on the mounting plate; the 24 V DC connection between the WB-PSU and the WB-AP is routed via terminals. This modular design allows for operation in two configurations: as a standalone cabinet on a mast with a direct traction power supply (750 V DC nominal) or as a simple, space-saving measuring set-up within an existing points cabinet with a 24 V DC auxiliary power supply.

Results/Benefits

Seamless long-term data logging: Automatic, continuous recording of the actual Traction Voltage with an adjustable sampling rate of 20 Hz to 1 kHz, rather than manual individual measurements
Proactive alerts rather than mere recording: Freely configurable monitoring thresholds (e.g. falling below 500 V DC) automatically trigger a notification via email or via WB-DO 4 – deviations are detected before they become a problem
Fail-safe thanks to battery backup: automatic switchover to battery power in the event of a mains power failure, with an event notification and a controlled shutdown when the battery is low – data and the system remain protected
Interference-free measurement in railway power supply environments: surge protection, interference filters and galvanic isolation between the power supply and the measurement platform ensure reliable measurement readings even in the presence of typical railway power supply interference
Versatile: Can be operated either as a cabinet mounted on a mast with a direct supply from the traction power system, or as a compact measuring unit housed in a points cabinet with a 24 V DC auxiliary power supply
Always accessible, even without an internet connection: a local web interface for configuration and operation immediately after the system starts up, regardless of whether there is an internet connection
Data where it’s needed: optional over-the-air transmission of measurement data via LTE, as well as escalation of critical operating conditions via text message or email

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