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3700 Portable Samplers
Section 3 Programming Guidelines
3.1 Description of
Sampling Operation
3.1.1 Sample Events and the
Sampling Cycle
3.2 Types of Samples
3-2
• The Run State section discusses what is occurring when
your 3700 is operating in the run state.
This information introduces the types of sampling performed by
the 3700 and the terminology that describes those capabilities.
A sample event is the complete cycle involved in taking a sample.
Although the cycle varies according to the program settings that
define the sampling routine, the cycle described here follows the
typical sequence. The information presented here is intended to
provide you with a frame of reference for the remainder of this
section.
1. A sample event occurs when either the programmed inter-
val has expired or programmed flow volume has passed
through the stream. The 3700 takes a time-paced sample
when an internal clock reaches the time selected for the
sample. For flow-paced samples, the 3700 takes a sample
after receiving a specific of flow pulses from the flow meter.
Each flow pulse counts for a specific flow volume as mea-
sured by the flow meter.
2. When the time interval expires or pulse count reaches a
user-programmed flow volume, the distributor moves to
the bottle that will receive the sample.
3. For the pre-sample purge, the pump rotates in reverse. The
pre-sample purge is an air purge of the suction line and
inlet that clears the line of any accumulated debris. It also
purges residual liquid to avoid cross contamination of sam-
ples.
4. The pump direction changes, moving forward to fill the
suction line up to the liquid detector.
5. The sample volume measuring portion of the sampling
cycle begins after liquid fills the suction line to the liquid
detector. The pump rotates forward until the programmed
volume of liquid is delivered to the sample bottle. (In this
manual, the amount of liquid delivered to the bottle is
referred to as the "sample volume.")
6. The pump direction changes, pumping in the reverse direc-
tion for the post-sample purge. Like the pre-sample purge,
the post-sample purge air purges the suction line. After the
post-sample purge, the pump shuts off.
7. The sample interval resets and the cycle resumes at Step
1.
The 3700 Sampler is principally designed to collect sequential
(discrete) samples. However, you can program it to collect a
number of other types of samples. The 3700 Sampler has two pro-
gramming modes: Basic and Extended. The basic programming
mode is used for conventional routines, which include the types
of sampling described in this section. Section 3.3 discusses this in
detail.
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