Valeport rapidPro CTD, Operating Manual

Page: 16 / 36

© 2019 Valeport Ltd
0660907a - rapidPro Operating Manual
Page 16
2.2.5. Turbidity
Valeport's Turbidity technology is essentially two sensors in one. The first is a “classic” nephelometer, using a 90°
beam angle for turbidity levels between 0 and 2000 NTU. The second sensor uses optical backscatter - OBS
(~120° beam angle) for turbidity levels beyond 10 000 NTU. Both sensors output data simultaneously, at a
programmable rate, so there is no need to switch ranges as conditions vary. Intelligent sampling and the use of a
24 bit ADC eliminates the need to switch gain. The optical head is very compact, measuring just 20mm diameter
and is rated to full ocean depth.
Excitation\Detection: 850nm
Linear Range: Nephelometer 0 to >1 000 NTU - linear response
Optical Backscatter: 0 to 6 000 NTU - linear response
(>6,000 NTU has a non-linear monotonic response that allows derivation of higher
values using look-up tables)
Minimum Detection
Level
0.03 NTU
2.2.5.1. Safety Statement
Valeport's turbidity sensor uses a near Infra Red (NIR) LED operating at 850 nm with a reflector producing a fairly
narrow output beam. As the photo-response of the eye is low at 850 nm the blink reflex and iris contraction reflex
are not activated. NIR LEDs generally produce very low levels of radiation and pose no threat to the human eye. A
photometric test report was commissioned by Valeport in accordance with BS EN 62471. For this the LED was set
to 25 times the operational power and the sensor was classified as exempt. However, it is best practice to avoid
extended exposure to the LED and it is recommended not to look directly into the sensor windows.
The Turbidity sensor is classified EXEMPT under the standard 62471.
As a Hyperion Turbidity instrument is classified as EXEMPT a hazard label in not required.
Never look directly into the Hyperion aperture