VTI Instruments EX1629, Руководство пользователя

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VTI Instruments Corp.
52 EX1629 Basic Operation
eliminates these tolerances as an error source. The strain accuracy tables are based on the
requirement that unstrained voltage measurement is performed.
The unstrained voltage measurement should only be taken once the bridge configuration and
excitation source parameters are established. It is critical that the operating conditions under which
the unstrained voltage measurement is taken be identical to those present during strain
measurement. That is, an unstrained voltage measurement taken before an excitation source
change would be mathematically invalid.
NOTE The unstrained voltage measurement should only be taken once the bridge configuration and
excitation source parameters are established.
The EX1629 components responsible for the unstrained voltage are primarily the completion
resistor and the main bridge measurement circuitry. And while they are of extremely high quality,
there is, nonetheless, a small temperature drift characteristic. For this reason, it is best to perform
the unstrained voltage measurement just prior to the initiation of strain measurements, making it as
fresh as possible. Moreover, to achieve maximum performance, it is best to allow the system
elements to thermally stabilize following an excitation source change before conducting its
measurement. For more details, see
Maximizing Measurement Performance in Section 1.
NOTE For maximum measurement performance, an excitation source change should be followed by a
thermal stabilization delay before the unstrained voltage measurement is performed.
While measuring the unstrained voltage is the conventional method of providing a value to the EU
conversion, it is also possible to manually enter a value. This would normally only be done for
system diagnostic purposes.
S
CAN
L
IST
C
ONFIGURATION
The EX1629 can be configured to include from 1 to all 48 of its input channels in the scan list.
Because of the channel independence present in the EX1629 design, there are no accuracy, noise,
or speed ramifications from the structure of the scan list. Its channel entries can consequently be
solely dictated by the user’s application requirements. Moreover, since the EX1629 features an
independent A/D converter per channel, input channels are, in a sense, not “scanned” at all.
Instead, the scan list simply dictates the specific data to be returned. The term “scan list” is
borrowed from traditional scanning (multiplexed) data acquisition systems. A valid scan list
consists of:
at least one channel
not more than 48 channels
no repeated channels
Each EX1629 input channel maintains its high input impedance and operational independence
from the other channels regardless of its inclusion in the scan list.
S
AMPLING
R
ATE
The EX1629 can be configured for a sampling rate from 1 Sa/s to 10000 Sa/s in 30 discrete
settings, regardless of the number of channels in the scan list. This permits the tailoring of the data
load to the dynamic requirements of the test application. The valid sample rates are 1, 2, 4, 5, 8,
10, 16, 20, 25, 33.33, 40, 50, 80, 100, 125, 166.67, 200, 250, 400, 500, 625, 833.33, 1000, 1250,
2000, 2500, 3125, 5000, 6250, 10000 and 12500 Sa/s. A rate of 25000 Sa/s can be achieved if 1)
the number of active channels is limited to a maximum of 16 and 2) all active channels are on the
same analog board (i.e. channels 0 through 15, 16 through 31, or 32 through 47 can be selected).
Requested rates that fall between valid ones are rounded to the closest valid one.