Precision Measurement Engineering, Inc.
Precision Measurement Engineering, Inc.
SCAMP contains special circuits that perform analog signal processing of selected channels. Normally there are two of these channels, each connected to a Fast T sensor. The analog processing consists of a gradient circuit (d/dt) followed by a programmable gain amplifier, followed by a 6-pole, 45 Hz, anti-alias filter. The outputs of these circuits are connected to SCAMP's "gradient" channels. The programmable gains must be adjusted by the customer in response to profile conditions.
Since ballasting and gradient gain depend upon actual environmental conditions they cannot be set in advance. Instead, preliminary profiles must be conducted, the results reviewed, and appropriate corrections made until the velocity and gradient gains are acceptable.
Preliminary profiles are conducted as described in the Profiling with SCAMP section of this manual. After data upload and storage, select the System tab from the SCAMP Control
Dialog. The screen shot below shows this tab.
This screen allows the user to view gradient plots, set gradient gains, and to view velocity plots. (Note that the plots result from the last profile uploaded from SCAMP at the beginning of this SCAMP Control Dialog. If the Dialog is begun and SCAMP has no profiles to upload, then the display buttons will be inactive.)
VELOCITY
Click the Display button in the velocity section. A plot of SCAMP’s velocity from the most recent profile will appear. SCAMP should ideally travel at 10 cm/sec. You may have to add or remove ballast weights to obtain this velocity. In Upwards mode, weights should be hung on the rods provided at the bottom of the drag plate. In Downwards mode, major weight adjustments should be made to the weights at the sensor end (see pictures below), but small adjustments may be made by hanging weights on the rods provided at the bottom of the drag plate.
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SCAMP’s velocity will not be constant throughout the water
column since the density of the water is different at different points. Try to make an
adjustment that gives 10 cm/sec in interesting regions.
GRADIENT GAIN
Click the Display button in the Gradient Channels section. A plot of the selected gradient channel from the most recent profile will appear. You must select the amount of programmable gain used in each gradient circuit. This gain cannot be set prior to field use since the gradients in the water column vary depending upon environmental conditions such as recent winds. The user must set the gain based on conditions actually observed in profiles, and should generally be aware that conditions can change hourly making gain settings obsolete.
The objective of setting gradient gains is to obtain signals from
the gradient circuits that occupy a large fraction of the A/D input range. The plot
presents the selected Gradient Channel plotted on a fixed range of +/- 1.0, where 1.0
represents full A/D count (32768). Try to select a gradient gain that gives 30% usage
without any data points reaching the A/D clipping value of +/- 1.0. Set the gradient gains
by entering them in the Gradient Gain box. Note that the gain you set here will only
influence future profiles and will not change the present plot or any already uploaded
profiles. Normally gradient gains for similar sensors (like Fast T0 and Fast T1) are set
equal to each other. In special cases gains can be set differently to capture different
sections of the water column. Note also that data obtained when the sensors are above the
water surface may contain very large gradients. Ignore these when evaluating the plot.
MONITORING CONDITIONS
When gradient gains and velocity are set you may use SCAMP for profiling. Velocity will not normally require modification as profiles are obtained. However gradients in the water column can change quickly in response to surface wind conditions. Profile groups should be uploaded from time to time and gradients reviewed to insure that they continue to be set appropriately for current conditions.
