Omega Engineering OMB-DBK-34A, Руководство пользователя

Страница: 42 / 250

Scan Group
Channel
(Immediate to
10 hours)
Scan Period
#7
x2
#18
x100
#19
x10
#16
x1000
#4
x8
10 s
µ
x8
#2
x1
#2
Digital
Input
Gain
Time
Time
All channels within scan group are
measured at 10 µs/channel.
Scan Rate
Most sampling of analog signals occurs on the timebase of the LogBook or the Daq device clock. The
scan period is the time duration between successive scans. Inversely, the scan rate , or scan frequency is
the number of scans per time interval, usually expressed in scans per second . The channels within the scan
are always sampled at a fixed period of 10 µ s (100 kHz rate), or 5 µ s (200 kHz rate); or 10 µ s for the /2000
Series Devices. Generally, the sampling frequency must be greater than twice the highest signal frequency
of interest to prevent aliasing error.
Note 1 : With /2000 Series Devices, either 100 kHz or 200 kHz can be selected to be used as the internal
clock speed. To ensure signal accuracy the 100 kHz speed must be selected when using a
DBK12, DBK13, DBK15, DBK19, DBK53 or DBK54 in conjunction with DaqBoard/2000
Series, or cPCI DaqBoard2000c Series boards.
Note 2 : Except in the case of a single-channel scan, the sampling rate per channel can be much slower
than the scan rate.
Triggering
Triggering controls an acquisition cycle. Once the system is armed, a trigger is required to collect the data.
Typically, three data collection parameters are specified: the pre-trigger count, the post-trigger scan count,
and the trigger source. The user must determine the triggering requirement based on the nature of the
measurement and the amount of data needed to satisfy the system’s purpose.
Trigger Event
Type of Trigger Source
Post-Trigger Scan Count
Time
Scan Period
(10 µs to 10 hours)
Pre-Trigger Scan Count
70 s µ
10 s µ
Immediate
Key Hit
External TTL
Channel Value - Rising
- Falling
•
The pre-trigger scan count specifies the number of scans that are to be collected before the trigger
point. If the pre-trigger scan count is greater than zero, the system will continuously collect data
until the trigger is satisfied. If no pre-trigger scans are required, the system sits idle until the trigger;
then, it collects the post-trigger scans before it disarms.
1-10 Signal Management
886995
DBK Option Cards and Modules