1. PCI/PCIe TFP Hardware
input reference. Modulation ratio, carrier frequency, impedance loading, and other effects may
degrade time code performance accuracy. Some applications require very high synchronization accu-
racy while using AM time codes as a reference. The following calibration procedure helps assure the
best time code synchronization accuracy. Because of the inherent differences in the time codes, a dif-
ferent calibration factor exists for each time code type. The user should determine which time code to
use in their system, and then perform the calibration for that code. The user can consult Sym-
metricom if unsure of which code type is best for their application.
1.3.8. Calibration Procedure
The following procedure uses the Windows based bc635PCIcfg.exe program to perform the adjust-
ments. This procedure will synchronize the on-time mark of an incoming time code reference with the
rising edge of an incoming 1 PPS signal. (The accuracy of this calibration is limited by the syn-
chronization of the incoming 1 PPS and the on-time mark of the incoming time code).
1. Connect the AM Time code reference to the Time code Input on J1 pin 7 of the TFP card.
2. Select the Format and Modulation type for the reference Time code (using the bc635PCIcfg.exe
pull down menu “Time code > Decode”).
3. Connect the 1 PPS reference to the External Event Input on J1 pin 6 of the TFP card.
4. Enable the External Event Input on the Rising Edge (using the bc635PCIcfg.exe pull down menu
“Signals > Events”, and select External Input and Rising Edge).
5. Read the minor event time (using the bc635PCIcfg.exe pull down menu “Time > Get Event
Time”).
6. Repeat the previous step to obtain an average value. You may have to average two neighboring
values (e.g., the average of x.000012 and x.000013 is x.0000125).
7. Convert the minor event time to a calibration factor. If the minor event time is close to rolling over
(i.e., x.999950), subtract 1 from the minor event time to get the calibration factor in microseconds
(e.g., -50 uS or 50E-6 sec); otherwise the minor event time is the calibration factor (e.g., X.000012
= 12 uS or 12E-6 sec).
8. Convert the units of the calibration factor measured in the previous step from microseconds to
hundreds of nanoseconds by multiplying it by 10 (12 uS = 120 hundreds of ns). x hundreds of nano-
seconds is equivalent to xE-7sec.
9. Set the Propagation delay on the card to the calibration factor in units of hundreds of nanoseconds
as calculated in the previous step (using the bc635PCIcfg.exe pull down menu “Time > Set Prop
Delay”).
10. Read the minor event time (using the bc635PCIcfg.exe pull down menu “Time > Get Event
Time”), and verify that the minor time reading is .000000.
If the minor event time is greater than ±1 uS, adjust the calibration factor as necessary.
Note: Keep this calibration factor and the associated time code type (i.e., IRIG B AM CAL = +120E-7)
in a safe place. If another time code type is to be used as a reference, a new calibration factor should
be determined for that code.
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