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Description
The Princeton Scientific Instruments (PSI)
Ultra Fast Framing CCD Camera is a high speed solid
state digital imaging system which employs a unique
focal plane array having the facility to store images
within the image sensor itself, thus circumventing the
bandwidth problems normally associated with high frame
rate imaging. The schematic
drawing of the focal plane array depicts four adjacent
pixels in the array. Each pixel consists of a photodetector
and a CCD type charge storage memory array. In one clocking
cycle, photoelectrons generated in the photodetector
are shifted into the adjacent charge storage site of
the pixel's memory array, thereby acquiring a frame.
The photodetector readout rate is also the frame rate.
As the frames are acquired the memory array is filled
by shifting the charge packets to the right and then
down in rows. The bottom row is dumped as new frames
are acquired, such that the most recently acquired images
are retained. An external or internal trigger stops
the acquisition mode, which is followed by readout of
the stored images at a slow rate to minimize readout
noise and to facilitate image data acquisition by a
conventional, low cost, PC type computer.
The system diagram
shows the Ultra-Fast Framing Camera System, consisting
of a camera head, electronics chassis, and camera control/data
acquisition computer. The camera
head drawing shows the overall configuration of
the camera head which contains the focal plane array,
cooled by a thermoelectric module, in a hermetically
sealed enclosure to prevent condensation. A mechanical
shutter, controlled by the camera electronics, is positioned
behind the optical lens to block exposure of the array
during readout. Various lenses can be accommodated.
Operation
The frame rate is selected by a keyboard
command in the range from <100 to 1,000,000 frames
per second. In normal operating mode,
the camera runs continuously, retaining in the image
sensor's CCD type memory, the last images acquired.
The image acquisition process loads new images into
each pixel's memory array in a first-in-first-out process.
When a trigger pulse is received, the over-writing stops
and readout of the stored images begins at a comparatively
slow pixel rate to minimize readout noise and to allow
data acquisition using inexpensive PC type microcomputers.
This pre-trigger mode of operation is a particular advantage
in capturing images of the beginning stage of spontaneous
events and other transient events whose timing cannot
be predicted to the required temporal accuracy for such
high frame rates. A mechanical shutter closes during
readout, blocking light from reaching the image sensor
during readout.
During readout the software sorts the multiplexed
image data as it comes from the camera to create the
image arrays in the computer's RAM memory. Once in the
computer memory, the images can be displayed individually,
as an array of images, or stepped through in continuous
loop mode to show the dynamic changes during the sequence.
The standard image format used to save the image data
is 16 bit FITS, but data can also be converted to 16
bit TIFF format if desired. There is an Ethernet output
for exporting the images to a network. This network
connection also allows remote operation of the camera
over a local network or even over the Internet. The
user interface is a web browser, which is used to send
operating commands, and receive image data for immediate
display.
Supersonic Turbulent
Flow Image Data
2003
American Physical Society (APS) Poster Session Paper
showing imaging data of edge turblence in NSTX and Alcator
C-Mod.
Click
here to see additional data taken with PSI's ultra-fast
framing cameras (courtesy Princeton University's Applied
Physics Group).
Alcator C-Mod Edge Turbulence results from
Princeton Plasma Fusion Lab (courtesy Stewart Zweben,
PPL):
- Click
here
for data taken with the PSI 4 FFCAM from 2003.
- Click
here for data taken with the PSI 3 FFCAM.
Click
here to see Gas puff imaging of edge turbulence
on NSTX using the PSI-4 camera.
(courtesy Stewart Zweben, PPL).
Click
here to see a sampling of recent PSI-5 camera images
from NSTX.
(courtesy Stewart Zweben, PPL).
| Image Sensor |
PSI patented CCD with on-chip storage
of 12 to 300 frames |
| Camera Head |
Thermo-electric cooled CCD |
| Control Chassis |
5 1/2" x 19" card cage containing
power supplies and electronics for control and operation
of the camera head |
| Control and Data Acquisition Computer
(Included) |
Intel Pentium class computer with
interface card for data acquisition directly to
computer memory |
| Frame Rate |
<100 to 1,000,000 frames per second,
software selectable |
| Trigger Modes |
Internal or External Pre/Post Trigger |
| Data Format |
12 to 300 digitized images per readout
which can be displayed locally and downloaded to
an internal "ZIP" drive, or accessed via
an Ethernet link |
| Video |
14 bit A/D |
The following versions of the Ultra-Fast
Framing CCD Camera System are currently available for
sale:
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PSI-3 |
PSI-4 |
PSI-5 |
| Max Frame Rate |
5 MHz |
~3 MHz |
~1 MHz |
| Array Size |
64 x 64 |
80x160 |
64x64 |
| Image Size, mm |
7.4 x 7.4 |
18.4x9.2 |
12.9x12.9 |
| Pixel pitch, microns |
116 |
115 |
202 |
| Storage Capacity |
12 frames |
28 frames |
312 frames |
| Optical Fill Factor |
48% |
48% |
33% |
| Readout Time, sec |
0.4 |
~3 |
10 |
| Readout Noise, rms |
~20e, rms |
~15e, rms |
~20e, rms |
| Buttable on 3 Sides for Mosaic Focal
Planes |
No |
Yes |
Yes |
|
Maximum Photoelectrons per Pixel
|
~30,000 |
~40,000 |
~40,000 |
Qe*
- at 256 nm 35%
- at 313 nm, 35%
- at 660 nm, 55%
- at 850 nm, 45%
Multiply Qe by optical fill factor for net quantum
efficiency. |
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