Installation; Theory Of Operation - Hach NV3300 User Manual

Theory of operation

The sensor uses two LEDs for long-term stable measurements of SAC values or color numbers at a
different wavelengths.
The light intensity of the LEDs usually changes with the temperature. The sensor uses a correction
factor for each different wavelength to calculate the measurement value. The absorbance is
calculated with the formula that follows:
A = -log T
10
T = I / I
0
where:
T = transmission in %
I = current light intensity
I = basic light intensity in ultra-pure water
0
A = absorption in AUs (absorbance units)
Based on the model, the sensor outputs the SAC (Spectral Absorption Coefficient) of the wavelength
of LED1. The wavelength and absorption of LED1 is labelled in the sub-index SAC
wavelength of LED2 is 740 nm. The scattering of light on particles in a solution is seen as turbidity.
The sensor uses the absorbance of 740 nm (A
measurement of the wavelength emitted by LED1. The SAC of each wavelength of LED1 is
calculated with the formula that follows:
SAC = (A – A
XXX xxx 740
where:
d = length of the optical path of the sensor in mm
SAC = spectral absorption coefficient in 1/m
Parameters Unit
SAC 436 1/m

Installation

Multiple hazards. Only qualified personnel must conduct the tasks described in this section of the
document.
Installation guidelines
Note: Make sure that the enclosure of the probe is titanium before use in sea water.
• Do not use stainless steel probes in sea water or other corrosion-causing media (e.g., acids,
alkalis, chlorine-based compounds). Clean the probe immediately.
• Do not use titanium probes in bromine, hydrofluoric acid and hot acids. Clean the probe
immediately if the probe touches hydrofluoric acid or hot acids.
• The seals of the probe are made of NBR (nitrile butadiene rubber). Make sure that the measuring
medium does not cause damage to the probe components.
• Do not replace the cable. If the cable has damage, contact the manufacturer.
• Make sure that the cable is not routed near hot surfaces. Make sure not to put heavy objects on
the cable.
• Make sure that there are no unwanted materials in the optical path.
4
In some applications it is necessary to enter a factor to scale the SAC at a specified
wavelength.
8 English
Table 2 shows the applicable parameters based on the sensor type.
) * 1000 / d
Table 2 SAC parameter
4
Factor LED 1 (nm)
— 436
) for the turbidity correction of the absorption
740
LED 2 (nm) In agreement with
740 DIN EN ISO 7887:2011_method B
C A U T I O N
and A . The
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