VTI Instruments EX1000A, Руководство пользователя

Страница: 61 / 320

www.vtiinstruments.com
EX10xxA Triggering 61
For voltage channels, similar results are seen. After taking 512 readings at each input voltage at
varying frequencies, the following typical noise profile can be seen.
Scan Rate ±10.0 V ±1.0 V ±0.1 V ±0.067 V ±0.010 V
200 Hz 0.0005 0.00005 0.000005 0.0000035 0.000001
500 Hz 0.0009 0.00009 0.000009 0.000006 0.0000012
1 kHz 0.0019 0.00019 0.000019 0.000013 0.0000019
T
ABLE
3-5: V
OLTAGE
M
EASUREMENT
N
OISE
P
ROFILE
V
S
. S
AMPLING
R
ATE
S
CAN
L
IST
C
ONFIGURATION
The EX10xxA can be configured to include from 1 to all 48 of its input channels in the scan list and
EX10xxA-51C can be configured to include from 1 to all 51 of its input channels in the scan list.
Because of the channel independence present in the EX10xxA/EX10xxA-51C 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. A valid scan list consists of:

at least one channel

no more than 48 channels for EX10xxA

no more than 51 channels for EX10xxA-51C

no repeated channels
A scan list entered via the embedded web page interface will be scanned in sequential order from
the lowest to the highest numbered enabled channel. For greater control, channels can be added to
a scan list in any order (although the channels will be scanned in numeric order once the scan list is
executed).
Each EX10xxA input channel maintains its high input impedance and operational independence
from the other channels regardless of its inclusion in the scan list. That is, the connection or lack of
connection to a valid input signal of unscanned channels makes no difference.
S
CAN
L
IST
T
IMING
Each scan sequence commences with the sequential measurement of the twelve CJC channels for
EX10xxA, regardless of the population of the scan list, the use of external CJC temperatures, or the
EU conversions employed on the input channels. The enabled scan list channels are then
individually measured. In order to provide the tightest time correlation possible between channel
measurements, the scan sequencer cycles through the scan list as fast as possible. Because of the
averaging mechanism discussed in
Sampling Rate / Noise Performance, the exact timing between
channels depends on the selected sampling rate. For reference, the interchannel timings for different
sampling rates are the following:
Sampling Rate Interchannel Timing (µs)
1 kHz 16.66666666
500 Hz 33.33333333
400 Hz 41.66666666
300 Hz 55.55555555
≤200 Hz
83.33333333
T
ABLE
3-6: I
NTERCHANNEL
T
IMING
V
S
. S
AMPLING
R
ATE
Applications that require maximum time correlation of transient signals will benefit from the
following suggestions to configure the unit for maximum speed:

set a sampling rate of 1 kSa/s

eliminate unneeded channels from the scan list

employ the 1 kHz setting of the hardware filter