Hach 900 MAX Appendix B, LCD Test, Liquid Sensor, Velocity Analysis, Page, Programming Features

Appendix B

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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