YSI Data Scout Advanced - Manual (Page 92)

YSI Incorporated Data Scout Advanced 88
This utility program converts selected uncompensated absolute pressures in an Original input data file, using a reference source of
absolute BaroScout pressure data with similar date/time profile. The conversion equations are as follows:
pBh = pB * (1 + h * D) (calculates head pressure per baro elevation)
p2 = p1 - pBh (subtracts baro head pressure from abs.press.)
Where: pB is the measured absolute pressure reading from the Barometer in psia,
pBh is the calculated “head” pressure at the surface of the water in psia,
h is the height (elevation) of Barometer above surface of the water in inches**,
D is the density per psi of dry air in pounds/in3, a constant (2.9315E-6),
p1 is the measured pressure of the transducer to be compensated in psia,
p2 is the final calculated compensated value of this transducer in psia.
**Note: the elevation may be a negative number if the barometer is located below the surface of a particular water well or lake. Such a
condition might exist if one centrally located barometer is used as a reference to a series of nearby lakes with different surface
elevations.
This convert program actually accepts pressures (in its input files) even if they are already expressed in pressure units other than psia.
It converts such other pressure units to psia before performing the calculations indicated above. The final compensated value is then
converted back to the original units before being written to the New compensated file. However, if the input files already have their
pressure data in psia, and the final result is desired in some other “level” units (e.g., ft H
2
0), convert the final “compensated” output file
separately with another Convert function. If you do this extra convert step immediately after the compensation is finished, the New
output file is automatically assigned as the default Original input file of the second Convert operation.
Initially, this window has its Convert button, and several other new buttons, disabled (dim) until both input files are correctly
specified. The Original and New file frames still have their default names automatically specified by the last file selected of DSPlay.
However, the new Barometer frame is normally blank (unless there have been previous conversion sessions which used the same file
name).
If the default Original file is not correct, the Browse button in this frame may be used select a different “uncompensated” data file
manually. The View/Edit button may be used to view the contents of the selected file (as text) at any time. This file must contain
absolute pressure data samples in order for the conversion to be meaningful.
The only possible default offered for the Barometer (second input) file is one that was selected during a previous conversion session
(without exiting DSPlay). This Barometer file is normally selected manually by using that frame’s own Browse and View/Edit buttons.
This second input data file is assumed to contain absolute pressure samples with date and time stamps that coincide with all the
absolute pressure data in the uncompensated absolute Original data file to be converted. In the special case of a Record file (containing
pressure data from multiple transducers) both frames may contain the same file name if one of the recorded transducers in the
common file is the desired absolute Barometer data.
Regardless of whether the Barometer data is in the same file or in a different file, if it contains data from multiple transducers, another
text box appears in the Barometer frame, to the right of the file name, to allow the particular transducer # containing the Barometer
data to be selected. The ToolTip of that text box indicates the range of valid transducer numbers that may be entered. If you change
this text box you must end your numerical entry with a <Tab> key before the change is actually made.
Normally, the Convert button is enabled as soon as any two input files (in the top two Original and Baro file frames) are specified and
found to exist. However, this does not mean that the compensation is successful. To be successful there must be available barometer
samples with date/time stamps that are at least “close” to the date/time stamps of the pressure samples being compensated.
For AutoLog data files, or Record data files with only one transducer recorded, the normal case is that two unique “input” files must be
specified. In this case, the Barometer file must have pressure data samples that coincide with the same range of dates and times
throughout the Original file within some specified “age” tolerance (which defaults to 10 minutes). If the file to be compensated has
pressure values with time stamps earlier than the first available barometer reading or has time stamps later than the last available
barometer reading, the tolerance is used to determine if that barometer sample is close enough to be used for the pressure
compensation. Any pressures that fail this criterion are not compensated, and its resultant data values are replaced with the non-value
token “**nobaro**”.