Hach 900 MAX manual Section, Example

Section 3

Flow Proportional Constant Time, Variable Volume Sampling (CTVV)

A Level-Velocity Sensor Input must be logged and electrically connected for the CTVV feature to work correctly.

CTVV samples are taken at user-specified constant (fixed) intervals. However the actual volume of each sampling is based on the known average flow rate of the site, the actual metered flow rate for each specific interval, the total sample volume desired, the user-specified collection period, and the specified Sampling Interval. Depending on the flow volumes of a stream and various intervals within the Collection Period, the volume of individual sampling can vary. Also, the total sample collected during the entire period can carry slightly above or below the Total Volume Desired. For these reasons, the manufacturer advises to use a sampling container that has a larger volume than the Total Volume Desired value.

•Sample Distribution menus are not available when CTVV is selected.

•A level-velocity sensor input must be logged and electrically connected for the CTVV feature to correctly work.

•The Flow Pacing Mode menu within the Flow Proportional menus sequence will not remember the previous setting whenever you re-enter this menu, it will revert to the CVVT default. When re-entering this menu, press CHANGE CHOICE to select the sampling method, CVVT or CTVV.

Example:

This is an example of how the instrument determines sample volume, based on user inputs and actual metered flow volume.

The user entered values are the following:

•Average Flow Rate (historical, site specific): 150 gph

•Sampling Interval: 2 minutes

•Total Sample Volume Desired: 1500 mL

•Collection Sampling Period: 30 minutes

Calculation 1: Total Number of Samples

----Sample----------------------Period-------------------	= 30---------min.---------- = 15 samples total within specified period
Sampling Interval	2 min.
Calculation 2: Average Sample Volume
Total----------------Sample----------------------Volume----------------------Desired-------------------=		------------1500---------------mL------------------	= 100 mL/sample
Total Number of Samples		15 samples Total
Calculation 3: Sample’s Volume per unit of Flow Rate
Avg.--------------Sample----------------------Volume-------------------= 100------------mL/Sample-----------------------------= 0.7mL/gph
Avg. Flow Rate		150 gph

Calculation 4: Actual Sample Volume to be Collected

Sample Volumes per unit of Flow Rate ⋅ Actual metered Flow Rate

0.7 mL/gph ⋅ 150 gph = 105 mL for this sample interval

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8990startup.fm	Basic Programming Setup