Enhanced CCD Cooling
CCD cameras come with thermoelectric coolers (TEC) to lower the imaging chip temperature down to -40C. However, when ambient temperatures are higher, such cooling is not possible. At +20C, TEC can get the chip down to -15C @ 80% cooling power; a good power spec to ensure a stable chip temperature to within +/- 0.1C. The QSI 516 has two, one-inch diameter muffin fans embedded into the CCD chassis heat sink. To cool the CCD chip, the TEC pipes heat away to the heat sink and the fans act to dissipate the heat from the sinks. Getting the CCD chip to -20C was not possible without the optional QSI liquid assisted cooling. As an alternative, a 120mm diameter muffin fan was attached to the rear of the camera (where the chassis heat sink fins are located) and usually operated at 25% of full RPM using a POT. Coolng the CCD chip to -15C (at +20C ambient) required only 61% cooling power. The 19% drop in cooling power (in actuality a 21% increase in available cooling power), can be used to lower the CCD chip to -20C while operating within the 80% cooling power spec. The graph below shows various the power curves for cooling the CCD chip under a range of ambient temperature conditions. The second graph shows the rate that cooling power throttles back (under constant ambient and CCD chip temperatures) after the muffin fan is switch on at 100% of its rated RPM.