Stamolys CA71SI
2
Hauser
Function and system design
Measuring principle upper
measuring range (SI-B)
After sample conditioning, the analyzer sample pump conveys a part of the filtrate to a mixing vessel. The
reagent pump adds reagent at a specific ratio. As a result of the reaction, the sample turns a characteristic
colour. The photometer determines the sample’s absorption of an emitted light at a specific wavelength (s. Fig.,
Pos. 2). The wavelength is parameter specific. The absorbance is proportional to the concentration of the
specified parameter in the sample (Pos. 3). Additionally, the absorption of a reference light is determined to
receive a genuine measuring result. The reference signal is subtracted from the measuring signal to prevent any
effects due to turbidity, contamination and ageing of the LEDs.
The temperature in the photometer is controlled thermostatically so that the reaction is reproducible and takes
place within a short period of time.
Measuring principle lower
measuring range (SI-A)
The LED sends light at a defined wavelength through the sample. The intensity of the received light is
measured by the detector and converted to an electrical signal. In the analyzer, the respective concentration is
calculated from the proportion of light absorbed by the sample.
Silicate
With 18% silicon is the second most frequent element of the earth crust. It occurs chemically bonded as silicate
or silicon dioxide in a variety of minerals. From these minerals silicate or silicic acid is washed out in low
quantities to waters.
There are no standard limits for drinking water since silicate is not known to be harmful to health.
But in boiler feed water and boiler water, there may be only low silicate concentrations because under thermal
charge or under high pressure insoluble silicon dioxide is formed. It solidifies in boilers, heat exchangers and
turbine blades and thus reduces the heat exchanger’s efficiency or causes overheating.
The standard limit for boiler feed water is 0.02 ppm silicic acid (SiO
2
). For injection and boiler water the
standard limits are pressure dependent. For example, at an operational pressure of 68 bar (986 psi), the
concentration of silicic acid in boiler water must not exceed 10 ppb.
a0001612
Photometric principle
1
2
3
4
5
Reference LED
Emitter LED
Sample
Reference detector
Measuring detector
a0001613
Photometric measuring principle
1
2
3
LED
Detector
Sample
1
2
3
