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3.5 Programming Steps
3.5.1 Pacing
3.5.2 Sample Every
__ Hours, __ Minutes
3.5.3 Sample Every
__ Pulses
To begin programming from the Main Menu screen, use the Next
or Previous button to select PROGRAM. Press the Enter button
to display the first programming screen. Refer to Figures 3-3 or
3-4 and the following descriptions.
There are two pacing methods for sampling programs:
• Time paced sampling programs use the sampler's
internal clock to collect samples at a constant time
interval. When you program the sampler for time
pacing, the sampler will prompt you to enter the time
between sample events in hours and minutes.
• Flow paced sampling programs require an electronic
signal from a flow measurement device. This electronic
signal is typically a pulse that indicates some
user-programmed volume interval has passed through
the flow channel. Because each pulse represents a
volume interval, flow pacing rates are proportional to
the volume of water flowing through the channel. This is
sometimes called "Constant Volume Variable Time
(CVVT) sampling." When you program the sampler for
flow pacing, the sampler will prompt you to enter the
number of pulses to count before collecting a sample.
Note
All Isco flow meters provide a compatible flow pulse. Non-Isco
flow measurement devices may be used to paced the sampler.
Refer to section 2.8, Connecting the Sampler to External
Devices, for more details.
Use the Next or Previous buttons to select the time or flow
option, then press the Enter button.
Time Paced Only – Use the Number buttons to enter the time
interval in hours and minutes. The sampler collects a sample
each time this interval elapses while the program is running.
Flow Paced Only – Use the Number buttons to enter the flow
interval as a number of pulses. While the program is running the
sampler counts the flow pulses until this number is reached. At
this time the sampler collects a sample and resets the interval to
begin counting again.
The volume that each flow pulse represents is determined by the
flow measurement device. With some instruments this volume is
user-defined; others use a fixed volume. Refer to the instruction
manual of the flow measurement device.
For example, consider an Isco 4250 Flow Meter programmed to
send a flow pulse every 100 gallons. If you are required to collect
a sample every 10,000 gallons, you would enter 100 flow pulses.
÷
10000 gallons
Isco 4700 Refrigerated Sampler
Section 3 Programming
100 gallons per pulse
=
100 pulses
3-13
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