YSI 650 MDS - Manual (Page 57)

YSI Incorporated 57 650 MDS
Once these conditions are met, follow the instructions in Section 5.3 above for logging of sonde sensor
readings to 650 memory. The GPS readings will automatically be added to the file at the sample interval
selected for the sonde readings.
GPS readings stored in 650 memory will remain as part of the sensor data file that can be viewed from the
650 display and/or uploaded with the data file for analysis in EcoWatch for Windows. Latitude and
longitude are, however, displayed somewhat differently by the 650 and EcoWatch as noted below:
•
For both display formats, the GPS are indexed relative to the point where the Greenwich Mean Time
line crosses the equator.
•
For the 650 Status Bar, readings are displayed in degrees and then decimal minutes relative to this
point with actual “N” (north), “S” (south), “E” (east) and “W” (west) designations relative to the index
point.
•
When analyzing data in EcoWatch, the user will have the choice of two formats, decimal degrees (e.g.,
47.5400 degrees) or degrees/decimal minutes (e.g., 47
o
32.400’). For EcoWatch, alpha directional
characters (“N”, “S”, “E”, and “W”) are NOT used. Instead, points north and east of the index point
are designated as positive, while points south and west are designated as negative.
These criteria mean that the GPS coordinates of Yellow Springs, Ohio, USA are approximately 39
o
47.33’
latitude and -83
o
54.13’ longitude as read in EcoWatch, but N 39
o
47.33’ W 83
o
54.13’ as displayed by the
650.
SECTION 9 USING THE 650 BAROMETER
9.1 PRINCIPLES OF OPERATION
The optional barometer operates on the strain-gauge principle and is located on the internal PCB of the 650.
To make certain that the barometer is sensing true atmospheric pressure under conditions of temperature and
pressure changes, the interior of the case is vented to the atmosphere with patches of material which are
permeable to air, but impermeable to water. One of these patches is located in the rear section of the case and
the other is attached to the battery lid. The patch on the case rear is not accessible to the user, but the one on
the battery lid can be damaged by abuse. Be certain to identify the location of the patch on the interior of the
battery lid and take care not to puncture it with sharp objects or to peel it away from the plastic. If you suspect
that the venting patch on your battery lid has been damaged, make certain that you do not expose the 650 to
water (either spraying or submersion). Then contact YSI Customer Service as soon as possible for advice.
The 650 barometer reads true barometric pressure and therefore is unlikely to agree with values from your
local weather service which are usually corrected to sea level before being distributed. Note, however, that
the primary purpose of the barometer is for use in calibrating your sonde dissolved oxygen sensor and the
“true” value as shown in the 650 Status Bar is the required parameter for this procedure.
9.2 CALIBRATING THE BAROMETER
The 650 barometer is factory calibrated to provide accurate readings in the 500-800 mm Hg range which will
be useful for dissolved oxygen calibration at most locations. This factory calibration should provide readings
that are useful for dissolved oxygen calibration for many months with no user attention. However, if the user
wishes to either increase the accuracy of the sensor in the local barometric pressure range or to compensate for