Teledyne 6712SR - Manual (Page 108)

6712SR Refrigerated Sampler
Section 5 Extended Programming
5-20
5.11.1 Calculating Variable
Sample Volume
Settings
The entry for the SAMPLE VOLUME display can be calculated
based on expected flow rates and collection volume requirements.
The number of pulses or flow module volume that you enter
should ensure that the minimum volume of liquid required for
analysis is collected without exceeding the bottle volume capacity
of the sampler. You may find it helpful to determine a range of
values by calculating both possibilities. The number you enter
would be selected from this range. This range is illustrated in
Figure 5-2.
Figure 5-2 Factors Affecting Flow-Weighted Variable-Volume Samples
In other words, at the greatest expected flow, this SAMPLE
VOLUME value should be set to prevent filling the bottle before
the end of the program. An early full-bottle condition would
result in a composite sample that is not representative of the
flow stream.
At the lowest expected flow, the SAMPLE VOLUME value should
be set to ensure that enough sample is collected. If too little
sample liquid is collected, there may not be enough for analysis
although it is a representative composite sample.
For example, consider an NPDES sampling program used to
collect a flow-proportional composite sample for BOD, TSS, and
NH
3
-N analysis. The laboratory requires at least 1,000 ml for
BOD, 100 ml for TSS, and 400 ml for NH
3
-N tests. The minimum
composite volume needed for analysis is then 1,500 ml, but to
allow for duplicates and spillage, this volume is doubled to
3,000 ml. The samples are to be collected over an eight hour
period at 15 minute intervals into a 9,400 ml composite bottle.
Flow rates at the site range from 1.5 to 2.0 mgd, the equivalent
volume of 500,000 and 666,667 gallons respectively over the
eight hour period. This flow is measured by an external flow
meter that sends a flow pulse every 100 gallons. Figure 5-3
depicts this scenario.
Total Bottle
Capacity
Minimum
Required Sample
Volume
Time
Fl
o
w
V
o
lum
e
Leas
t Ex
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Flo
w
Gr
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tes
t E
xp
ec
ted
Fl
ow