HBM DI Serie Bedienungsanleitung Seite 11

11
DI...
In 1989, the first practical use was discovered for so−called "writing", that is,
inscribing periodic structures into the cores of optical glass fibers. Such fiber
Bragg gratings (nanotechnology) in the core of monomode crystal fibers
established an important field in fiber−optic sensor technology.
n
Grating period
core
∆nX10
n -4
eff
Λ
Input light Reflected light Transmitted light
Bragg wavelength
0.1 − 1 nm
λ λ λ
λ λ
B B
Fig. 1.2: Working principle of a fiber Bragg grating
The basis of the working principle is that the radiant light, in a range of 1510
nm to 1590 nm, for example, is reflected rather than transmitted by the fiber
Bragg grating at a quite specific wavelength. This wavelength is the so−called
Bragg wavelength.
The fibre core is surrounded by a cladding of purest glass with a diameter of
125 µm. To confine the light in the core, the refractive index of the core must
differ from that of the cladding. The gratings are inscribed in the core. The
wavelength reflected by a strain gage is stated on the packaging. In
conjunction with interrogators − which are opto−electric (photonic) analyzers −
it is possible to condition the strain signals with high, static accuracy and
long−term consistency (SI... product family) or with high precision and dynamic
performance (DI...product family). These signals, together with physical
measured quantities which may be determined by transducers with other
principles of measurement, are acquired and processed with the

catman Easy/AP measurement and analysis software.
As with fiber optics it is possible to transmit mutually unaffected spectral
information, the signals (wavelength variations) of several optical strain gages
can also be transmitted in a single fiber. A fiber of this type with several strain
gages is called an optical sensor chain. So several measuring points can be
operated with a single connection on the interrogator, such as CH1.
A2301-1.2 en/de HBM