VTI Instruments EMX-4016B, Руководство пользователя

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VTI Instruments Corp.
APPENDIX B 52
O
VERLOADS AND
O
PEN
T
RANSDUCER
D
ETECTION
When the analog signal amplitude exceeds the input range, the digitized samples are truncated
resulting in a distorted waveform. To avoid this, users can increase the input range of the instrument,
attenuate the signal level, or discard overloaded data from processing. Apart from over-range, there
are other fault conditions that can invalidate measurement data, such as open transducer. EMX-
4250/4350/4380 is capable of detecting some of these common fault conditions and reporting it,
allowing the user to act.
The fault status can be queried from the digitizer and DSA driver’s API. The status can be indicated
at the front panel LED. The information is also associated to the acquired data record and returned
in
AdditionalData string.
The digitizer and DSA drivers define each fault status as an Overload Status bit field. The user can
configure which fault conditions to reported, if an LED indicator is shown, or it can latch so that the
momentarily fault won’t be overlooked.
Bit Field Description EMX-4250/51 EMX-4350 EMX-4380
0x00000000 Within the range - - -
0x00000001 Signal level less than next
lower input range No No No
0x00000002 Exceed upper transducer
limit No No No
0x00000004 Exceed lower transducer
limit. No No No
0x00000008 Exceed upper user limit* Yes Yes Yes
0x00000010 Exceed lower user limit* Yes Yes Yes
0x00000020 Open Transducer IEPE only IEPE only** IEPE only**
* User limit detection occurs right after ADC at the top span, before decimation filtering.
** Open transducer is detected at around 100 ms - 200 ms interval with EMX-4350/4380.
Table 4-1: General Fault Status Bit Support
Bit Field Description EMX-4250/51 EMX-4350 EMX-4380
0x00010000 ADC overload (This
includes differential and
common mode overload) Yes Yes Yes
0x00020000 Hardware common mode
overload No Yes Yes
0x00040000 IEPE transducer short IEPE only IEPE only* IEPE only*
* IEPE short is detected at around 100 ms - 200 ms interval with EMX-4350/4380.
Table 4-2: Instrument-Specific Fault Status Bit Support
T
IME
S
TAMP
During data acquisition, the EMX-4250/4350/4380 returns timestamps along with digitized analog
data. The timestamps are created based on the
TimestampSource clock specified in
ReferenceOscillator interface. When IEEE 1588 synchronized time stamps are desired, the
TimestampSource property must be set to ReferenceOscillatorTimestampSourceSystem . Otherwise,
the time returned will be the time elapsed since the SYNC signal was received.
When measurement data is retrieved, both a timestamp of the data record and a timestamp of trigger
event are returned. The combination of
TimeSeconds and TimeFraction parameters indicate the time