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Why is the water jacket warmer than the imaging chip when the cooler is turned off?
The water jacket dissipates heat not only from the electronic coolers, but also from the electronics—mostly the power supplies. The temperature difference shows that the electronics are generating heat and the imaging chip is thermally isolated from them.
How long does it take for the temperature to stabilize?
Typically it takes 300 seconds or less to go from room temperature to a 30C temperature differential.
What does "Rate of change" measure?
The rate of change is a slowly decaying number that helps you determine when the temperatures have stabilized. The Trifid Control Panel multiplies the once per second change in temperature difference by 100 and then applies an exponentially decaying filter that takes about 30 seconds to stabilize. Whenever the rate of change is less than two, the temperatures have nearly stabilized.
What is the difference between the water jacket and the imaging chip temperatures after the temperature stabilizes?
Typically you will see a 30C difference or more.
Does the maximum difference change if I cool the water pumping through water jacket?
Some, but not a lot. The electronic coolers are temperature differential devices, but their efficiency does drop as the water jacket temperature drops. If the water jacket is at room temperature they are about 45% efficient. If the water jacket temperature drops to 0C, their efficiency drops to 28%. At -20C their efficiency drops to less than 5%. At a certain point the efficiency drops to the point where they cannot remove enough heat to cool the imaging chip anymore.
Can I cool the liquid pumped through the water jacket to below freezing?
Yes you can, and this will lower the dark current, but beware of cooling the camera too much. When you cool the water jacket, you cool the entire camera, which includes the window in front of the imaging chip. If this window is cooled below the dew-point it will collect dew or frost. If you live in a dry climate you can cool the water jacket more than someone who lives in a moist climate. The dew-point temperature will tell you where you can expect to start encountering problems. In practice, a fairly air-tight telescope will allow you to lower the temperature below the dew-point before you start to see a buildup of moisture.
If you are interested in cooling the water jacket further than the dew-point will allow, contact us about machining an extra port in the camera body so you can feed a continuous stream of dry nitrogen across the face of the window.
How much does the noise drop as the imaging chip is cooled?
There are three types of noise that infect an image: shot, thermal and readout noise. There is not much we can do about shot noise because it is a part of the incoming light. Increasing the exposure length so as to average the photon rate over more seconds will improve the signal to noise ratio. Readout noise is set by the design of the imaging chips and the camera. Thermal noise—what is called dark current—is the one noise we can lessen in the field, by cooling the imaging chip. For every 6C we cool the imaging chip, the noise is cut in half.
Is the imaging chip temperature regulated?
The duty cycle of the thermal electric coolers can be adjusted either manually or automatically. In the automatic mode you set a desired imaging chip temperature and the duty cycle of the thermal electric coolers is automatically adjusted to obtain and maintain that temperature.
Should I turn off the electronic coolers during image readout?
Turning off the coolers during readout is a good practice because it eliminates any noise they might be inserted into the image during the analog-to-digital conversion. But you don’t have to worry about it because the Trifid driver already does this automatically during each readout. As soon as the readout is complete, the coolers are reset to their last duty cycle.
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