Agilent Technologies 1100 Series Reference Manual page 226

6 Introduction to the Detector
Spectrograph
The spectrograph material is ceramic to reduce thermal effects to a minimum. The
spectrograph consists of the spectrograph lens, the variable entrance slit, the grating and
the photodiode array with front-end electronics. The spectrograph lens refocuses the light
beam after it has passed through the flow cell. The sampling interval of the diode array
is < 1 nm over the wavelength range 190 – 950 nm. Depending on the wavelength this
varies from 1.0 to 1.25 diodes per nanometer (for example a diode every 0.8 to 1 nm).
For a small wavelength range, the small non-linearity could be neglected. With the
wavelength range from 190 – 950 nm a new approach is required to achieve wavelength
accuracy over the full range. Each spectograph is calibrated individually. The
calibration data is stored in the spectrograph on an EEPROM. Based on these data, the
built-in processors calculate absorbance data with linear intervals (1.0, 2.0, ...) between
data points. This results in an excellent wavelength accuracy and instrument-to-
instrument reproducibility.
Variable Entrance
The micro-slit system makes use of the mechanical properties of silicon combined with
the precise structuring capabilities of bulk micro-machining. It combines the required
Slit System
optical functions — slit and shutter — in a simple and compact component. The slit
width is directly controlled by the micro-processor of the instrument and can be set as
method parameter.
Grating
The combination of dispersion and spectral imaging is accomplished by using
a concave holographic grating. The grating separates the light beam into all its
component wavelengths and reflects the light onto the photodiode array.
Diode Array The diode array is a series of 1024 individual photodiodes and control circuits located on a
ceramic carrier. With a wavelength range from 190 – 950 nm the sampling interval is <
1 nm.
226 1100 Series DAD and MWD Reference Manual