58 PI-MAX/PI-MAX2 System Manual Version 5.F
smaller arrays). Also, if the lab is particularly warm, achieving temperature lock
might take longer or not be obtainable at all.
Supplemental Water-cooling: Allows temperature lock to be achieved more rapidly
than would be required to lock at the same temperature with air-cooling alone. In
addition, it will be possible to achieve temperature lock at lower temperatures,
typically three or four degrees lower than would be possible with air-cooling alone.
Cooling performance can be enhanced by circulating water with a temperature below
laboratory ambient but this approach will increase the risk of condensation inside the
PI-MAX. This condensation can cause catastrophic failure of the detector electronics. Any
resulting damage would be considered to have resulted from improper operation and will not
be covered by the Warranty. Even ordinary tap water is too cold to be used without risk! For
safety, the water should be no colder than the laboratory ambient temperature. Closed
circulation systems that depend on ambient air-cooling of the circulating water will generally
give good results. If you feel that you must use water colder than the laboratory ambient
temperature, it is absolutely essential that the PI-MAX be operated where the humidity is low
enough to prevent internal condensation. If the coolant is below the freezing temperature of
water, we advise using a mixture of 50% water and 50% ethylene glycol as the coolant.
The easiest and most practical way to achieve the required low humidity is to put the
PI-MAX inside a plastic bag and to then purge the bag with a continuous flow of dry
nitrogen. On completion of the experiment, be sure to continue the purge until the
PI-MAX’s internal cold surfaces have had time to warm to the ambient laboratory
temperature. Contact the factory if you require additional information.
See "Making the Coolant Circulator-Camera Connections", page 44 for additional
information regarding the use of water with a temperature below laboratory ambient.
Setting the Temperature
Regardless of the type of cooling, the CCD array temperature is set via the software
Detector Temperature dialog box, accessed by selecting Detector Temperature on
the Setup menu (WinView/32 or WinSpec/32). Temperature lock to a set temperature in
the operating range will typically occur within ten minutes. Perhaps another twenty
minutes will be required for maximum temperature stability to be achieved. To see when
the array temperature reaches and stabilizes at the target temperature, leave the Detector
Temperature dialog box open. When the target temperature is reached, the dialog box
will report that the Current Temperature has Locked.
Note: If you are using the USB 2.0 interface, the Detector Temperature dialog box
will not display temperature information while you are acquiring data.
Exposure
Data acquisition has two parts: exposure and readout. Exposure refers to the integration
of a signal of interest on the CCD array and readout is the transfer of the integrated signal
from the array pixels to a shift register and from there to a preamplifier. During exposure,
each pixel in the two-dimensional grid of individual pixels senses the intensity of light
falling on its collection area and stores a proportional amount of charge in its associated
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