Paragon-X: How do I make a 1PPS measurement against an external reference?

The Paragon-X can measure an input 1PPS signal for accuracy against another 1PPS signal, or stability against an external frequency (e.g. 10MHz) reference. The 1PPS measurement accuracy in both cases is 1 nanosecond.

For making phase measurements both the reference signal and the measured signal must be 1PPS.

Measuring a 1PPS for stability against a frequency reference is of limited utility, however it can be of use in checking a clock status (i.e. a basic check “is the 1PPS source clock locked or free-running?”).

If the Paragon-X is in thru-mode, any packets received on the Ethernet ports will be captured if they match the configured flow filter, or if no flow filter is set all packets will be captured. Capture of packets may result in reduced test duration and unwanted capture data.

If no packets are required to be captured, the filter at the bottom of this article can be applied to pass all packets without capturing them.

Prerequisites

The instrument must be licensed with the correct option to be able to make the required type of 1PPS measurement:

  • Option 206: 1PPS vs 1PPS, absolute accuracy measurement

  • Option 205: 1PPS vs Frequency, relative stability measurement

 

Paragon-X Configuration

1PPS measurements against an external reference can only be made when PTP Emulation (MSE) is not running. In MSE mode, the Paragon uses the external 1PPS for measurement trigger start, and top-of-second alignment for PTP generation. See the linked article for more information on this behaviour: https://calnexsolutions.atlassian.net/wiki/spaces/KB/pages/5439492

To configure the Paragon-X for a 1PPS measurement:

  1. Set Operating Mode to 1588v2, ensure the “Enable Master/Slave Emulation” box is not checked:

     

  2. Navigate to the Setup Interface screen, then References tab to configure the reference signal parameters:

     

    1. For a 1PPS vs 1PPS measurement, the 1pps Reference Input is the reference signal. The Clock Source is not used in the 1PPS measurement, however it may be used for other concurrent measurements (e.g. SyncE).

    2. For a 1PPS vs Frequency measurement, the Clock Source is the reference signal and must be set to External (Ext.). The 1pps Reference Input is not used.

  3. Navigate to the Measurement Ports tab to configure the 1PPS measurement input parameters:

     

  4. From the Measurements screen, select the type of measurement that is being made:

     

    1. For a 1PPS vs 1PPS (accuracy) measurement select 1pps Time Error (Absolute)

    2. For a 1PPS vs Frequency (stability) measurement select 1pps Time Error (Relative)

  5. From the Configure Capture screen, if making a 1PPS Time Error (absolute) measurement, enter the cable delay for each signal, and configure a measurement pass/fail threshold if desired.

 

Making a measurement

Follow the relevant process below depending on which type of measurement is being made.

1PPS Accuracy (Absolute) Measurement

This feature can be used to measure phase accuracy. This is done by comparing a recovered 1pps (from a PTP subordinate, for example) to a GPS reference.

  1. Connect the 1pps from the Slave to the Measurement port and a 1PPS reference signal to the Reference input.

  2. Ensure that the “1PPS Ref” and “1PPS Meas” LEDs in the status panel are green

  3. Press Start Capture

  4. Select Graph Context = 1PPS/GP

  5. Select Graph > Graph Display Mode > 1PPS Accuracy

1PPS Wander (Relative) Measurement

  1. Connect the GPS 1PPS reference to the Measurement port, and a stable frequency reference (e.g. 10MHz) to the Reference input.

  2. Ensure that the Ref and 1PPS Meas LEDs in the status panel are green

  3. Press Start Capture

  4. Select Graph Context = 1PPS/GP

  5. Select Graph > Graph Display Mode > 1PPS Wander

 

Results

Example results are shown in the screenshot below.


Flow Filter for no packet capture in thru-mode

While making a 1PPS measurement, if it is required to pass packets through the Paragon-X without capturing any then the filter below can be applied to achieve this. The filter is for a reserved MAC address therefore no packets will match.

The following filter definition file is required:


To apply the filter definition file:

  1. From Flow Filter, click on Set

     

  2. Import the No_Packet_Capture.cfd file and click Apply All