Sigma 900 MAX Refrigerated Sampler Instrument Manual

Appendix B
Page 123
8990apdx_pfeatures.fm Programming Features
LCD Test
Display Test allows you to verify that all pixels in the Liquid Crystal Display
(LCD) are functional. The LCD is made up of 14,400 pixels that are turned on
and off as needed to create the display of graphics and text. Each individual
pixel is turned on and off by its own transistor, which means that if a transistor
failed, the pixel might not turn on, which could cause an unreadable or
confusing display.
Selecting LCD Test from the Diagnostics menu will cause the display to
become black for 3 seconds. This allows verification that all pixels are
functional. A defective pixel will stand out as a white dot in the field of black
dots. A message, “The display will remain inverted for 3 seconds” is shown for
2 seconds followed by a 3 second period with all dots turned on.
Liquid Sensor
The liquid sensor contains a high frequency sound transmitter and receiver.
High frequency sound waves are sent through the silicone pump tubing by
vibrating a piezo-electric crystal. They are picked up on the other side of the
tubing by a receiving crystal acting much like a microphone. Since sound
waves travel much more efficiently through a liquid than they do through air,
the receiving crystal gets a much louder signal when water passes through
the tubing in the sensor. The signal from the receiving crystal is converted to a
voltage which is proportional to the signal strength. This voltage is used by the
sampler microprocessor to sense the exact moment water reaches the
sensor. the liquid sensor compares the voltage (signal strength) when the
tubing is dry (such as when purging the line) to the voltage when the tubing is
full of water (such as when pumping a sample). The dry verses wet voltage
reading must be at least 0.8 V dc higher than the 0.3 volts, then when the
voltage needed to sense liquid would be 1.1 volts or higher.
The Liquid Sensor is designated as #1. The diagnostic screen displays the
voltage coming from the sensor electronics. Should a problem arise where the
liquid sensor is not reliably sensing the liquid, (inaccurate sample volumes,
water getting to the bottle during an intake rinse, purge failure), use of the
Liquid Sensor diagnostics values will provide valuable information as to the
sensor sensitivity.
Velocity Analysis
A velocity probe must be installed in the flow stream and be connected to the
meter in order for this diagnostic to work. This diagnostic allows viewing a
‘real time’ reading directly from the Submerged Area Velocity Probe. It will
show the current velocity Signal Strength (percentage of Doppler signal
returning to the probe) and a ‘real time’ velocity measurement of the flow
stream. Use this diagnostic to determine if the probe is mounted for optimal
velocity measurement. The closer to 100% the Signal Strength is, the more
stable the velocity reading will be. If the signal seems low (50% or less), it may
be due to improper installation of the probe or a lack of particulate in the flow
stream.
11:00 AM 21 - APR - 01 VELOCITY ANALYSIS
SIGNAL STRENGTH: 90‰
VELOCITY: 7.00 fps
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