What Is BND?

BND (Blinking/Noise/Dimming) Error Detection

This error detection function supplements the unique firmware sampling and digital filtering method for sensing the field input signals. The NSM SIGNAL MONITOR field input sensing algorithm is designed to filter out relatively short term noise transients commonly found on the electrical service and provide noise immunity against false signal detections. The BND Error Detection function is designed to detect and respond to irregular input waveforms which exhibit a longer time constant in comparison to the short term digital filtering time constant. This detection algorithm is intended to detect a signal that is: irregularly Blinking (flickering); has constant extraneous Noise; or is Dimmed invalidly under Controller Unit software control. These signals are differentiated in part due to the large time constants which may be associated with these irregular input waveforms and may indicate a malfunctioning component or improper operating mode within the cabinet assembly.

The BND Error Detection function is designed to recognize many of these possible input waveforms and will place the NSM SIGNAL MONITOR into the fault mode. If the aforementioned signal conditions exist for a pre determined period of time, the NSM SIGNAL MONITOR will enter the fault mode, transfer the OUTPUT relay contacts to the Fault position, enable the Stop-Time output to the controller, and illuminate the BND FAIL indicator. The NSM SIGNAL MONITOR will remain in the fault mode until the unit is reset by the RESET button or the EXTERNAL RESET input. An AC+ brownout condition or a complete loss of AC+ power will reset the BND fault state of the monitor. The Channel Status display will indicate the channels on which the fault occurred.


Blinking

This blinking or flickering signal condition may exist under certain abnormal circumstances such as: controller output malfunction (i.e. output toggling, pinwheeling, etc.); load switch malfunction (output shorting intermittently, zero cross failure, phase firing, etc.); intermittent field wiring or NEUTRAL return (due to corrosion, poor termination, improper or poor cabinet grounding system, etc.). Another cause of flickering occurs when excessive AC voltage to a channel input in the OFF state occurs due to load switch "leakage current" and high load impedance. This high impedance load may be caused by dimmers, low wattage loads (7 watt test lamps, solid state loads, etc.), poor wire terminations, etc.. When the voltage level of a field input signal is near the threshold level of the input comparators, AC ripple and noise may produce a flickering effect.

NOTE: When the voltage level of a field input signal is reduced to within approximately 100 mV of the threshold level of the input comparators, the front panel channel indicators may flicker due to ac ripple and cause a BND error to be detected. This input threshold level may lie between 17Vrms and 23Vrms. The Traffic Control Systems Specifications (NEMA TS 1 1989) states that the input monitoring circuitry may or may not detect within a voltage range of 15Vrms to 25Vrms. To assist in testing and calibration a "BND Test Disable" option can be used to disable the BND function. This is for test purposes only. The NSM SIGNAL MONITOR should not be operated with the BND function disabled.


Noise

Constant high energy noise or transients on the field signal inputs may affect the integrity of the input sample if it occurs exactly within the narrow sampling "window" of the NSM SIGNAL MONITOR. Depending on the severity and repetition rate of the input noise, a BND error may be detected after the samples have been corrupted for a period of 90 to 200 line cycles.

This condition may not always be due to extraneous input noise. A faulty input comparator device may also result in reading invalid sampling data.


Dimming

The sampling and filtering algorithm allows ONLY half wave (positive or negative) suppressed dimming. Other dimming waveforms may be achieved under cabinet controller software control and will be detected as a BND error within approximately 90 periods of the input waveform.


Trouble Shooting A BND Fault

The BND fault can be difficult to trouble shoot and could result from at least the following:

  1. It could be a damaged signal monitor input.
  2. It could be a flickering output of a load switch.
    1. Try replacing the load switch or swap it with another load switch and see if the BND problem follows the load switch.
  3. The Off-state voltage of the RYG signals on a channel should all be less than 10 Vrms.
    1. Measure the voltages at the RYG field terminals when the colors are Off, and if any are at or above ~17 Vrms it could be a leakage issue.
  4. If the BND problem seems to be related to wet weather conditions, be sure that the field wires and any splices for the RYG on the affected channel are all dry and intact.
    1. Water pooling in a pull-box or conduit with splices can conduct through the water and result in Off-state leakage voltages on the field terminals.
  5. Be sure that all of the field wires for RYG on the affected channel are tight if compression screws are used.
  6. If the affected channel has its own Neutral return wire, make sure it is connected securely and no problems with splices or terminations.
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