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Configuring an IRIG Input

VersaSync supports up to four IRIG RS485 inputs, or up to to one IRIG DCLS/10V and up to two IRIG DCLS/TTL inputs. Supported IRIG input formats are A, B, and G (DCLS and AM). Furthermore, supported are inputs with frequency/resolution values of no carrier/index count interval, 1kHz/1ms, 10 kHz/0.1 ms, and 100 kHz/10 ms, as well as IRIG input coded expressions of the fields BCDTOY, CF, SBS, and BCDYEAR.

The IRIG inputs support the following coded expression combinations for BCDTOY, CF, SBS, and BCDYEAR fields:

  • 0 – BCDTOY, CF, SBS
  • 1 – BCDTOY, CF
  • 2 – BCDTOY
  • 3 – BCDTOY, SBS
  • 4 – BCDTOY, BCDYEAR, CF, SBS
  • 5 – BCDTOY, BCDYEAR, CF

Configuring an IRIG Input

While a quick status overview for an IRIG input can be obtained via the HOME Reference Status panel, a more detailed status view is available under INTERFACES > IRIG Input [x].

To configure an IRIG Input:

  1. Navigate to INTERFACES > REFERENCES: IRIG Input [x]. The Status window will open, displaying the current validity of the TIME and PPS reference, and currently configured settings:
  2. Click the Edit button in the lower left corner to open the Edit window:

The following configurable settings are available:

  • Format: Sets the formatting of the IRIG input signal, as defined by the IRIG generator time source. The available choices are:
    • IRIG A
    • IRIG B
    • IRIG G
    • NASA-36
  • Modulation Type: Configures the type of input signal modulation. The choices are:
    • IRIG DCLS Only: A TTL (Phase) modulated signal.
    • IRIG AM Only: An amplitude modulated signal.
  • Frequency: The IRIG modulation frequency. This is determined by the configuration of Format and Modulation Type. See IRIG Carrier Frequencies for details.
  • Coded Expression—Defines the data structure of the IRIG signal, where:
    • BCD = Binary Coded Decimal
    • TOY = Time of Year
    • CF = Control Field
    • SBS = Straight Binary Seconds
    • The available options will vary according to the configurations of Format and Modulation Type.
  • Control Function Field: IRIG signals have an optional section in the data stream that can be used to include additional information (such as the present year, for example). This field allows the Control Field section of the IRIG output to be defined. The available configurations are:
    • Fields conform to RCC 200-04: IRIG spec 200-04 specified a location for year value, if included in this field.
    • Fields conform to IEEC 37.118-2005 (IEEE 1344): Control Field contains year, leap second and daylight savings time information.
    • Fields confirm to Spectracom IEEE C37.118-2005: Has been extended to support one-month leap second notification.
    • Fields conform to Spectracom Format: Year is included in Control Field but not in the same location as RCC-2004 output (year is offset by one position).
    • Fields conform to Spectracom FAA Format: A unique IRIG output Control Field that contains satellite lock status and time error flags.
    • Fields conform to NASA Formats: Variants of IRIG B

    The available options will vary according to the configurations of Format and Modulation Type.

  • Note: If the Format value is changed, the Control Field and Coded Expression change to the default values for the given Format value. You can only change the Control Field and Coded Expression values to allowed values for the Format field.

    It is recommended that the VersaSync administrator/operator only use this if they do not know what the IRIG Input Format is, and they wish to identify the signal type, or to determine if a signal is present.

  • Local Clock: The incoming IRIG input time information may be provided as local time, but System Time may be configured as UTC time, so internal computations need to be performed. With the Timescale field set to “Local”, select the name of a previously created Local Clock. The Time Zone and DST rules, as configured in the Local Clock will be applied to the front panel time display.
  • Offset: Provides the ability to account for IRIG cable delays or other latencies in the IRIG input. The Offset value is entered and displayed in nanoseconds (ns). The available Offset range is -500 to +500 ms.

Configuring the IRIG Input Year

The IRIG time source may be able to provide VersaSync with the current year information via the IRIG input data stream. As the year value is not a required field in the IRIG data stream, (and if the year value is present, it may not always be in the same location of the Control Field), if the year value is contained in the control field section of the IRIG data stream, the control field “layout” needs to be defined in VersaSync (as determined by the Coded Expressions and Control Field values). If the year value is not present in the IRIG input signal, the year value will need to be manually set in VersaSync when using IRIG input as the only input Time reference.

Note: By default, the “year” fields in the IRIG message are ignored and a user-defined value is used.

Note: Make sure the year is set correctly when the VersaSync is installed. If the year is not set correctly before NTP achieves time synchronization, it will use the value entered. The unit will also default to the year entered if it is powered down during the rollover of the year. If the VersaSync was not switched on during the rollover, this value must be updated.

Note: When the IRIG Input year is updated, NTP must be restarted from the Web UI NTP page (or the VersaSync unit rebooted) for the New Year value to take effect.

To manually enter the current year value:

  1. Navigate to MANAGEMENT > OTHER: Time Management.
  2. In the System Time panel on the left, click the GEAR icon to open the Edit System Time window.
  3. Check Set Year Only, and enter the Year.

The Year value only needs to be manually entered once, as it will automatically increment to the next year each New Year’s day.