Hach FH950 Manuel D'utilisation De Base page 18

Option Description
Files This option is used to view or delete stored files. Files can be deleted all at once or
individually.
Setup This option is used to set up or change the settings for filter parameters and the
Maximum Depth feature.
3. Set up—Select this option to change general system settings and preferences.
Option Description
Velocity Calibrates the sensor. Adds a field offset to the factory calibration. Refer to the
calibration appendix in the expanded version of the manual for more information.
Filter Applies a data acquisition filter (Main filter or Pre-filter). The user can select the
parameters filter parameters.
Main filter
• Fixed Period Averaging (FPA)—Fixed Period Averaging averages data over
• RCA time constant—The RC filter helps smooth out turbulence through the
Pre-filter
• Median filter—The filtering process is done in the sensor. The feature can
Wet/dry Sets the sensor submersion threshold for wet and dry conditions. The default
threshold value is 20%. Refer to the appendix in the expanded version of the manual for
more information.
Auto zero Sets the Auto Zero feature to On or Off.
depth
If set to On, the instrument does an air calibration when the sensor is removed
from the water and is in the air. To do the air calibration, the instrument
automatically zeroes the sensor.
If set to Off, the user can manually zero the sensor. To do this, remove the
sensor from the flow, then push and hold the Quick Jump key for five seconds.
When the sensor has been in the flow for 30 minutes, the green circle in the
upper right corner goes from green to red. This is a prompt to the user to
remove and zero the sensor again.
EMI Sets the local line frequency for ambient noise rejection to 50 Hz or 60 Hz
(default).
Clock Sets the date and time of the portable meter in 24-hour format. Daylight
savings time is not supported.
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a user selectable fixed period of time (1 to 480 seconds). The default is
10 seconds. If the FPA value is 5, the velocity value shown in the display is
updated once every 5 seconds.
use of a selected time constant in the filter algorithm. This mode is useful
when searching for a maximum velocity, for example in the common 0.9 x
Vmax profile method. High RC filter time constants give higher degrees of
smoothing. The time constant can be set from 2 to 20 seconds, with a
default value of 6. At 1 time constant, the filter settles to approximately 60%
of the final value. At 5 time constants, the filter settles to 99.9% of the final
value. Thus, if the RC value is set to 2, the final value shows after
10 seconds.
be disabled. However, the recommended (default) value is 5. Enable the
feature to enter or change this value.