Waters 2996, Operator'S Manual

Page: 55 / 84

Measuring Light at the Photodiode 33
4
Figure 4-3 Photodiodes Discharged by Light
The 2996 Detector measures the amount of current required to recharge each photodiode.
The current is proportional to the amount of light transmitted through the flow cell over
the interval specified by the diode exposure time.
Exposure Time
The 2996 Detector recharges each diode and reads the recharging current one diode at a
time. The interval between two readings of an individual diode is the exposure time. The
2996 Detector requires less than 10 msec to sequentially read all of the diodes in the array
and process the data. The minimum exposure time is 10 msec. You can set exposure time
from 10 to 500 msec.
For example, if an exposure time is set to 50 milliseconds, the 2996 Detector:
1. Recharges diode 1 and reads the current required to recharge diode 1
2. Recharges diode 2 and reads the current required to recharge diode 2
Deuterium
Lamp
Flow
Cell
Sample in flow cell
absorbs at specific
wavelengths.
Light from grating
dispersed into 1.2-nm
wavelength beams
continuously
discharges diodes.
Grating
Mirror