10.2 Event and 1 PPS Deviation Recording
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10.2.4
1 PPS Deviation Measurement Principle
The measurement technique employed for 1 PPS Deviation uses the same time determination and recording
scheme used for event time measurement (refer to paragraph above), but makes the assumption that the input
signal is periodic and continuous. Also, the operation of the circular memory buffer is modified somewhat, in
that recording does not stop after the buffer is full; new Event Data is given priority over existing data, and
will overwrite it. Since the incoming signal occurs once per second and the circular buffer holds a number
of events, each event time record will be overwritten on a regular basis.
Once every second, the processor looks at the most recent group of 16 events. When computing deviation,
it uses only the portion of the event data describing fractional seconds (e.g. values between 0.0000000 and
0.9999999 seconds). By normalizing the 16 fractional second values around 0.0000000, the range of results
from the deviation computations will be centered on zero (-0.4999999 to +0.5000000 seconds). Statistical
computations are then performed on the 16 values to determine their Mean and Sigma (Standard Deviation)
values, which are then displayed on the front panel or output via the Utility software.
10.2.5
Event Timer Input Channel Configuration
In order for the clock to receive an event at one of the input connectors, adjustments to both the hardware
and software configuration may be required. The hardware configuration is described in Section 5.2.7 and
Section 5.2.6.
10.2.6
Firmware Setup
To display of Event Time Data or 1 PPS Deviation, use . See Figure 8.18 for detail on configuring the
Event/Deviation parameters from the front panel. See Section 11.2.3 for details on using the RS-232 interface.
10.2.7
Displaying Data
Event and deviation data can be accessed from either the front panel or via the clock utility software or
RS-232 commands. The following paragraphs describe the steps required to access data using the front
panel.
1. Press the TIMING key until reaching EVENT/DEVIATION menu, then press ENTER.
2. Press the UP or DOWN keys to scroll through the recorded events.
CH A EVENT
#
nn TZ
ddd:hh:mm:ss.sssssss
Where:
nn = event number (01 to 25)
ddd = day of year of the event (1 to 366)
hh = hour of the event (00 to 23)
mm = minute of the event (00 to 59)
ss.sssssss = second and fractional second of the event (e.g. 59.9999999)
TZ = time zone: either UTC or LOCAL
To scroll through any recorded events presently stored in the event-time buffer, press the UP or DOWN
key. If the event display mode is exited and then re-entered, the first event data displayed for a given channel
will correspond to the same event number as was last displayed for that channel. However, the data itself
may be changed if it has been overwritten.
