Waters ACQUITY UPC2, Overview And Maintenance Manual, Page: 12 / 84

8
Photodiodes discharged by light:
The 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 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 detector requires less than 5 msec to sequentially read all
of the diodes in the array and process the data. The minimum exposure time is
5 msec. You can set exposure time from 5 to 500 msec. For example, if an
exposure time is set to 50 milliseconds, the detector performs as follows:
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.
3. Sequentially recharges and reads the current required to recharge all
the remaining 510 photodiodes.
4. Waits approximately 45 msec before beginning the
recharge-and-reading sequence, with diode 1, after all diodes are
recharged and read.
Flow cell
Deuterium lamp
Light from grating
dispersed onto
diodes.
Sample in flow cell
absorbs at specific
wavelengths.
Grating
Mirror
Slit