ADLINK PCI-9820 - Manual (Page 41)

Operation Theory
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may recognize the trigger signal with one-clock time difference because the
signal is not related to the timebase.
There is another phenomenon if using TRSRC_SSI_2 in pre-trigger and
middle-trigger mode. The operation start signal is generated by a software
command so multiple PCI-9820 devices don’t start the data acquisition si-
multaneously, which may result in the fact that the amount of stored samples
are different if the trigger event occurs before the specified amount of data
has been acquired.
When selecting TRSRC_SSI_2 as the trigger source input, SSI_TRIG2 and
SSI_START_OP can achieve a better synchronization between multiple
PCI-9820 devices. A clocked SSI_TRIG2 can guarantee all PCI-9820 de-
vices recognize the trigger event at the same clock edge if they use the same
timebase. In pre-trigger and middle-trigger mode, SSI_START_OP guaran-
tees all the PCI-9820 devices start the data acquisition at the same time.
4.8 Auto-calibration
By using the auto-calibration feature of the PCI-9820, the calibration software
can measure and correct offset and gain errors without any external signal
connections, reference voltages, or measurement devices.
After the auto-calibration procedure finishes, the calibration constants can be
saved into the EEPROM. In addition to the default bank of factory calibration
constants, there are three extra user-modifiable banks in the EERPOM for
users to store three sets of calibration constants according to different en-
vironments and re-load the calibration constants when necessary.
Because of the fact that errors in measurements will vary with time and
temperature, it is recommended that users re-calibrate the PCI-9820 when
the card is installed in a new environment.
Note
: Before auto-calibration procedure starts, please warm up the card for
at least 15 minutes.