Photometrics SenSys, Руководство пользователя, Страница: 22 / 48

Chapter 4. Component Descriptions
13
total time any part of the CCD is exposed) is equal to the shutter open and close
times plus the exposure time.
The shutter is the only mechanical component that has a limited life with heavy
use. Instructions for testing and replacing the shutter are in
Chapter 5.
Troubleshooting.
Electronics
The CCD produces an analog signal. The camera electronics convert the analog
signal into a digital signal, data that can be received by the host computer.
Several factors influence what portion of the analog signal translates into digital
data. One factor is the noise in the camera system. The system noise includes the
thermal noise produced by the camera components and the read noise
determined in part by how far the analog signal must travel. The farther an
analog signal has to travel, the more the signal degrades.
To reduce signal degradation, SenSys has low-noise electronics and primary
point digitization (PPD
™
). The PPD design positions the analog-to-digital
converter (ADC) as close to the CCD as possible, which reduces the distance the
analog signal must travel.
Another determining factor is the quality of the signal received by the ADC. If
the ADC receives a high-quality signal, the 12-bit ADC digitizes the analog
signal into 12-bit data. With a lesser quality signal, the ADC produces data with
a lower effective bit depth.
The SenSys camera produces an analog signal that uses the full range of the
12-bit ADC (up to 4096 gray levels). Through software, the camera can be set to
High Sensitivity (Gain 3), High Dynamic Range (Gain 2), or High Signal to
Noise Ratio (Gain 1) detection modes. Each gain setting configures the camera
to be responsive to different light-level intensity ranges. The appropriate range
is dictated by the specific use of the camera.
No matter how fast the data moves from the CCD to the ADC, the camera
readout rate is determined by how quickly the ADC converts the data to digital
form. The SenSys has a 1Mpixel/sec conversion rate.
Input/Output
Trigger Port
The SenSys camera has a TTL input/output (I/O) trigger port that is located on
the back of the camera. (See diagram on next page.) When the camera is
shipped, this port is fitted with a black plastic cover.
The I/O port allows you to synchronize the camera trigger signal with external
equipment. Strobes, external shutters, and filter motors are examples of external
triggering devices. The I/O port is a male, D-subminiature 9-pin connector.
Pinout specifications are located in
Input/Output Port Pinout on page 29.