We have engineered Southern Technologies defect detectors and magnetic wheel transducers to work together for optimal performance over the system's lifetime.
Magnetic wheel transducers use electromagnetic induction to generate signals; a voltage is produced in an electrical conductor placed in a varying magnetic field. The wheel transducer has a permanent magnet wrapped in a precise number of turns of wire. Since the magnetic field is stationary, the transducer produces no voltage until a passing wheel causes the magnetic field to move through the winding.
The greater the rate of change in the magnetic field, the higher the signal level produced by the transducer. So signal strength is proportional to train speed – the faster the train, the stronger the signal. The strength of the magnet and the number of turns of wire also affect signal strength.
Not necessarily the most powerful magnet available, but a sufficiently strong magnet of known strength is key to predictable performance. In production, we qualify each magnet using a magnetometer with calibration traceable to the National Institute of Standards and Technology to ensure they are within the specified range. We wind each magnet in a specified number of turns of enamel-coated wire and seal the sensor inside the transducer housing using a potting procedure developed to secure the sensor for railroad working conditions.
The 2100-550 consists of a horseshoe magnet with a tightly wound coil encapsulated in a rigid epoxy potting compound. Each transducer is mounted 1‑9/16 inches (3.97 centimeters) below the top of the rail. As the wheels of a railcar pass over the transducer, the wheel flange disturbs the flux field of the magnet, causing the output of a sinusoidal type waveform of varying amplitude. The depth of the flange and the speed at which the wheel is moving determines amplitude.
The timing signals from the transducer are used to:
- Detect a train's presence
- Coordinate bearing and wheel temperature measurements
- Determine a train's direction
- Calculate a train's exit speed
- Calculate a train's length
- Identify individual railcars and locomotives based on axle spacing patterns
