Hach SIGMA 900, User Manual

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8837int.fm
Introduction
Section 1 Introduction
1.1 Instrument Description
The Sigma 900 All Weather Refrigerated Sampler is designed to
automatically collect and preserve samples from a liquid source using
refrigeration. The sampler is suitable for collection of conventional and toxic
pollutants and suspended solids.
The sampler is designed for indoor and outdoor applications. Conforming to
NEMA 4X, 6 standards, the controller withstands submersion, corrosion, and
ice resistance. Refrigeration components are polymer coated, providing
superior corrosive resistance. With the compressor and condenser located
above the refrigerated compartment, heat transfer is directed away from the
compartment. A microprocessor controlled thermal system maintains samples
at EPA mandated 4 °C (39 °F). Top mounted refrigeration components also
minimize exposure to the corrosive plant environments.
1.2 Principle Operation
The sampler uses a liquid sensing system to detect the absence or presence
of liquid at the peristaltic pump intake. The liquid sensor (
Figure 1 ) is located
on the front of the control housing. For liquid sensor troubleshooting see
Appendix A on page 61 .
The liquid sensing system provides three primary benefits:
• Accurate, repeatable sample volumes
• Intake tube prerinse
• Sample retry
Figure 1 Liquid Sensor
1.2.1 Accurate, Repeatable Sample Volumes
The liquid sensor detects the presence and velocity of the incoming sample.
This information allows the sampler to automatically dispense the correct
amount of liquid into the sample bottle.
The liquid sensing system allows the sampler to deliver repeatable sample
volumes even with changing suction lifts. Each time the peristaltic pump pulls
a sample, the microprocessor determines the time required for liquid to travel
to the liquid sensor. If the suction lift increases due to a drop in level at the
1. Sensor Body 2. Knobs (turn to remove) 3. Sensor Cover
2
1
3