Hach 900 MAX manual Section, •The sensor is first used

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.

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