K-Patents PR-33-S - Manual (Page 5)

1 Introduction 1
© Copyright K-Patents 2015. All rights reserved.
1 Introduction
The inline refractometer sensor PR-33-S (figure 1.1) measures the refractive index n
D
and the temperature of the process medium. The concentration of the process liquid is
calculated from these values when the composition of the process medium is known.
The output values of the sensor are transmitted through its Ethernet connection by
using a UDP/IP protocol (see chapter 2). An optional mA output unit is also available.
Figure 1.1 PR-33-S sensor
1.1 Principle of measurement
The K-Patents inline refractometer determines the refractive index n
D
of the process
solution. It measures the critical angle of refraction using a yellow LED light source
with the same wavelength (589 nm) as the sodium D line (hence n
D
). Light from the
light source (L) in Figure 1.2 is directed to the interface between the prism (P) and the
process medium (S). Two of the prism surfaces (M) act as mirrors bending the light rays
so that they meet the interface at different angles.
The reflected rays of light form an image (ACB), where (C) is the position of the critical
angle ray. The rays at (A) are totally internally reflected at the process interface, the rays
at (B) are partially reflected and partially refracted into the process solution. In this way
the optical image is divided into a light area (A) and a dark area (B). The position of the
shadow edge (C) indicates the value of the critical angle. The refractive index n
D
can
then be determined from this position.