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3.2.1 Types of Sample Pacing
3.2.2 Types of Sample
Distribution
Figure 3-1 Sequential Sample Distribution
You can characterize sample types by sample distribution and
sample pacing. Sample distribution is the order in which samples
are placed in the bottles. Sample pacing is the interval between
samples.
There are two types of sample pacing: time-pacing and
flow-pacing. In time-paced sampling, the interval between
samples is a time interval. In flow-paced sampling, the interval
between samples is a certain volume of liquid that has passed a
measuring point in a flow stream. Flow-paced sampling requires
a flow meter. (You can interface the 3700 Sampler with Isco Flow
meters, flow loggers, and certain non-Isco Flow meters.) The flow
meter measures the flow quantity and sends a pulse for every
predetermined flow quantity to the sampler. The sampler
totalizes the number of pulses received from the flow meter and
collects a sample when the total reaches a programmed number.
There are two primary types of sample distribution: sequential
and composite sampling. In a sequential sample, each bottle
receives one sample. A sequential sample represents a
"snapshot" of the flow stream at a particular point in time.
Figure 3-1 shows a diagram of sequential sample distribution. In
a composite sample, the individual samples are combined – "com-
posited" – into a single container. A composite sample represents
an average of the characteristics of the flow stream over the total
elapsed time of sampling.
Bottle Number (8 of 24 Bottles Shown)
1
2
3
1
2
3
Sample Event Number
Note
The 3700 Sampler is fully programmable for both sequential and
composite sampling; however, in addition to programming the sam-
pler for composite sampling, you must convert the 3700 Standard
sampler mechanically for single-bottle compositing. This requires
the composite conversion kit which contains the extra equipment
needed to adapt the sampler for composite sampling. Conversion
procedures are discussed in the instruction sheets provided with
the conversion kit. With the 3700 Compact, you merely insert the
bottle into the base.
3700 Portable Samplers
Section 3 Programming Guidelines
4
5
6
7
4
5
6
7
8
8
3-3
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