Sigma 900 MAX Refrigerated Sampler Instrument Manual

Page 64
Submerged Area/Velocity Sensor
8990sensors.fm
Section 4
7. Set the Velocity Units (fps or m/s), using the UP and DOWN arrow keys.
Press
ACCEPT to continue.
8. Highlight Velocity Cutoff, using the
UP and DOWN keys. Press SELECT.
9. Read the Velocity Cutoff information screen. Press any key to continue.
10. Set the Velocity Cutoff using the numeric keypad. Press
ACCEPT.
11. Set the Velocity Default, using the numeric keypad. Press
ACCEPT. Press
RETURN to go back to the Setup Menu or Main Menu to return to the Main
Menu display.
4.2.3 Submerged Area/Velocity Submerged Area/Velocity Sensor Calibration
This calibration requires a graduated cylinder or bucket with at least
16 cm (6 in.) of water and a ruler. Calibrating the Submerged Area/Velocity
Sensor characterizes the sampler electronics to the unique characteristics of
each individual sensor. In addition, the calibration compensates for any
sensor drift that may occur over time (6 months or greater) as the materials in
the sensor age.
The Submerged Area/Velocity Sensor is a pressure transducer that contains a
stainless steel diaphragm. As the water pressure increases, (with increasing
level in the flow stream) the diaphragm is deflected, or pushed, against a solid
state device called a strain gauge. The strain gauge converts the pressure
against the diaphragm to a voltage. As the level in the flow stream increases,
so does the voltage coming from the Submerged Area/Velocity Sensor. The
voltage is read by the microprocessor in the sampler at regular intervals and
converted to a number that represents the level in the flow stream.
The manufacturer recommends calibrating the submerged area/velocity
sensor when:
• The sensor is first used.
• Installing a new or different sensor on a flow meter or input receptacle.
• The difference between the level reading of the flow meter and the
independent verification (measurement with a dipstick or ruler)
is increasing.
Note: The data is constant if the difference between the level reading of the flow meter
and the independent verification is constant; recalibration is not required.
Note: Errors can occur with the flow meter level reading and the independent
verification. Errors are caused by variation in site conditions and measurement
abilities. These errors may cause slight changes in the difference, therefore, not
indicating a true change in the difference.
1. From the Main Menu, select OPTIONS > ADVANCED OPTIONS >
CALIBRATION > SUBMERGED PROBE.
2. Place the sensor flat on a table top or floor with the sensor (the plate with
holes) facing down onto the surface (Figure 17). Press any key to
continue.