Aquaprobe
®
AP-700, AP-800 & AP-2000 Instruction Manual
10401-00870 Rev R
The turbidity sensor's transmitter emits very short pulses of light in the infra-red spectrum at
a wavelength of 850nm that are invisible to the human eye. The sensor's receiver includes
a visible light filter, which filters out all visible light and allows the infra-red pulses from the
transmitter to enter freely.
The sensor's receiver is also AC coupled so it will only react to the very short, intense
flashes of light emitted by the transmitter. Under normal circumstances, visible ambient
light (from artificial lighting) is filtered out and any background infra-red light (sunlight) is
ignored.
However, all things have their limitations, and if very strong sunlight is allowed to enter the
measurement chamber from below and shine directly onto the turbidity sensor, the receiver
can become maxed-out or saturated.
This situation is rare, but can occur if the sensor is sitting on or near the bottom in shallow
water in direct sunlight where the sunlight can be reflected back into the Probe by light
coloured sand or pebbles.
Sensor saturation can result in negative turbidity readings as the magnitude of the
measurement light pulses are clipped (or reduced) by the upper limit of the sensor.
If this occurs, either lift the Probe up and away from the surface reflecting the sunlight or
shade the Probe from direct sunlight.
28.8. Top Tips for successful measurements using optical electrodes
➢
Always keep the measurement chamber and electrode lenses clean.
➢
Always fit the sleeve and end cap during both calibration and measurement.
➢
Always allow the readings to settle completely during both calibration and
measurement.
➢
Always try to eliminate air bubbles by agitating the Probe after insertion both during
calibration and measurement.
➢
Always calibrate and zero the electrode as close to your sample temperature as
possible.
➢
Always zero the optical electrodes just prior to use in clean water (bottled still
mineral water is ideal) then deploy
without disturbing the measurement chamber
.
© 2017 Aquaread
®
Ltd.
www.aquaread.com
Page 140 of 141