Princeton Instruments PI-MAX 3 System, Manual, Page: 34 / 150

34 PI-MAX
®
3 System Manual Version 1.A
System On/Off Sequences
The following on/off sequences are specific to the Ethernet interface:
1. The PI-MAX3 power supply must be turned on before the WinX application
software (WinView/32 or WinSpec/32) is opened to ensure communication between
the controller and the computer. If the WinX application is opened and the
PI-MAX3 power supply is off, many of the functions will be disabled and you will
only be able to retrieve and examine previously acquired and stored data. You must
close the WinX application software, turn on the power supply, and reopen the
WinX application software before you can set up experiments and acquire new data.
2. The WinX application software must be closed before turning off the power supply.
If you turn off the power supply before closing the WinX application software, the
communication link with the PI-MAX3 will be broken. You can operate the
program in a playback mode (i.e., examine previously acquired data) but will be
unable to acquire new data until you have closed the WinX application software,
turned on the power supply, and then re-opened the WinX application software.
Pre-Exposure Removal of Accumulated Charge
Introduction
The purpose of the CCD array is to acquire a signal of interest that can then be digitized
and transmitted to the host computer for storage, display, and post-processing. It will
acquire signal whenever the camera has power, whether or not the intensifier is being
gated to take an exposure. If the intensifier is off, dark charge will be the main source of
signal accumulation on the array. To counteract this, clean cycles, and continuous clean
cycles are used to remove the dark charge while the camera is waiting to acquire the
signal of interest. Dark charge, clean cycles, and continuous clean cycles are described in
the paragraphs that follow.
Dark Charge
As soon as the PI-MAX3 camera is powered on, thermally-induced charge will begin
integrating on the CCD array even if the photocathode is biased off. Because dark charge
is thermally-induced, reducing the array temperature significantly reduces the rate at
which this charge accumulates in the pixel wells. Even so, enough dark charge could
accumulate in the pixels between data acquisitions to affect dynamic range at the
beginning of an exposure. To prevent this from happening, clean cycles repeatedly shift
and discard any signal that has integrated on the array PI-MAX3 is waiting for a Start
Acquisition command from the host computer.
After the Start Acquisition command is received, a final clean cycle occurs and exposure
begins. During the exposure, both the signal of interest and dark charge integrate on the array.
The longer the exposure and the warmer the camera, the larger and less uniform the dark
charge will appear. To minimize the dark charge contribution to the acquired signal, you
should operate with the lowest temperature possible for your camera. Reducing the gate width
may also be helpful.
To further reduce the dark charge contribution to an acquired signal, you may be able to
perform background subtraction, which subtracts a dark charge background from raw
data acquired using the same experiment conditions (see
"Background Subtraction" ,
page 38).