SonTek/YSI
84
ADVField Operation Manual (September 1, 2001)
Calibration is performed by running the program
ADFCALAO
(see
ADVField Software Manual
), or
by using the
Cal
command from the direct command interface (§3.5). Either will set the analog
outputs to three predetermined voltages corresponding to the maximum negative velocity, zero
velocity, and maximum positive velocity. The voltages measured by the data acquisition system
at these three settings can be designated Vneg, Vzero, and Vpos. The calibration voltage values
can then be used when computing velocity values from the following formula.
2/)(
VnegVpos
VzeroVmeas
RangeVelocity
−
−
×=
If the calibration voltages are measured with a very accurate voltmeter, or a precision A/D con-
verter (more than 12-bit resolution), the zero velocity calibration can be used to verify the linear-
ity of the analog outputs. The linearity check is expressed as
[Vzero - 0.5*(Vpos - Vneg)]
and should be less than Vpos / 2048.
5.5. External Synchronization
ADV data collection can be synchronized with other instruments using the SyncIn and SyncOut
signals. SyncOut is a ≈1 ms, 5V pulse at the completion of each sample. For example, if the
ADV is collecting data at 25 Hz (sampling interval 40 ms), it will average pings for 39 ms and
then raise the SyncOut line to signal the completion of a sample. If precise synchronization is
important, you must take into account that the SyncOut pulse occurs at the end of the sampling
interval, while the measured velocity corresponds to the center of the averaging interval.
The SyncIn signal permits external control of ADV sampling. Two control options are available:
at the start of ADV sampling on receipt of an input pulse (
Start on Sync
) or full external control
of the data collection rate (
Sample on Sync
). An externally supplied 5V TTL pulse is normally
used to trigger data collection; alternatively, the 5V supply (accessed from the auxiliary I/O con-
nector; §4.3) can be used with a remote switch to start data collection at the push of a button.
The SyncOut signal is always generated by the ADV for any operating parameters. The SyncIn
line is treated differently by the ADV depending on the synchronization setting. The setting can
be changed either in the data acquisition software (see
ADVField Software Manual
) or using the
command
SyncMode
(§3.6). There are three settings:
•
Disable - The ADV ignores the SyncIn line and data collection starts under software control.
•
Start on Sync - The ADV waits for the rising edge of a 5V pulse on the SyncIn line to start
data collection. Data collection then proceeds under software control at the user-specified
sampling rate. The rising edge of the first pulse triggers the start of the first sample. Any fur-
ther signals on the SyncIn line are ignored.
•
Sample on Sync - The ADV outputs a sample after the rising edge of each 5V pulse on the
SyncIn line. The first rising edge triggers the start of the first sample, the second rising edge
triggers the end of the first sample and the start of the second sample, and so on. In this man-
ner, the sampling rate of the ADV is completely controlled by the SyncIn signal. The ADV
does
not
record or output the accurate time with each sample.
To Next Page
Loading...
Need help?
General
