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3700 Portable Samplers
Section 3 Programming Guidelines
3.9.5 Liquid Detector
You can use the Liquid Detector configure option to turn the
liquid detector on or off, set the number of rinse cycles, add a
suction-head setting to the program sequence, and set the
number of sampling retries should the suction line become
clogged. The option uses four input displays. Each display is dis-
cussed below.
Enable/Disable Detector – Teledyne Isco recommends setting
the Enable/Disable Detector option to "ENABLE." The 3700
Sampler determines the delivered-sample volume suction head
by counting revolutions of the peristaltic pump rotor. The volume
of liquid delivered by one revolution of the pump rotor is a
function of the suction head; as the suction head increases, the
volume delivered by one revolution of the pump rotor decreases.
By enabling the detector, the sampler can accurately determine
the operating suction head. It does not have to rely on a pro-
grammed suction-head value, but can instead begin its volume
delivery count when it detects liquid. This minimizes inaccu-
racies that can occur in changing head conditions, or when it is
difficult to measure the suction head accurately.
The disable option is provided should the detector or its asso-
ciated circuitry become suspect. If you disable the detector, the
manual suction-head setting (Display #70) is automatically
added to the Sample Volume program section in the program
sequence. If the detector is disabled, the sampler uses a calcu-
lated number of pump counts based on the suction-head entry to
deliver the correct sample volume. With the detector disabled,
the sampler operates at diminished accuracy. (Display #240)
Rinse Cycles – The Rinse Cycle setting is available only when
the detector is enabled. It sets the number of suction-line rinses
from 0 to 3. Rinses are used to condition the suction line to
reduce cross contamination. During a rinse cycle, the pump
draws liquid up through the line until the liquid detector senses
it. At that point, the pump reverses to purge the line. This cycle
repeats according to the number of rinse cycles entered (Display
#241). Rinse cycles contribute to the wear on pump tubing;
therefore, if you use rinse cycles, you may need to replace the
tubing more frequently. The Tubing Life configure option allows
you to monitor pump-tubing wear.
Enter Head Manually – When the detector is enabled, you can
optionally enter the head manually, allowing you to add the
suction-head entry (Display #70) to the program sequence.
When the detector is disabled, the Suction Head entry is auto-
matically added to the program sequence. By disabling the
suction-head setting, you allow the liquid detector to determine
the operating suction head each time a sample is taken.
When the head is stable and known accurately, you can further
increase the accuracy of the delivered volume by using the
Suction Head entry in conjunction with the liquid detector. When
the head is variable or unknown, select "NO" because an
incorrect head setting will diminish the delivered volume
accuracy. (Display #242)
3-41
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