A Temperature Control System of an EMCCD Cold Finger

An EMCCD is a highly sensitive CCD image sensor. At certain high operating temperature dark currents are generated in an EMCCD, reducing the signal-to-noise ratios of images taken by the device. For this reason, the operating temperature needs to be kept as low and stable as possible. This is accomplished by regulating the temperature of a CCD cold finger. The paper presents a new design of a temperature detection and control system of a cold finger. To fit the actual situation, we use certain aluminum material to make an EMCCD cold finger. This paper shows its structure and assembly steps. A platinum resistor Pt1000 is used as a temperature sensor, which is combined with three resistors of the same type and a potentiometer to constitute a bridge gauge. Based on the characteristics of the platinum resistor and the network structure of the bridge gauge, we deduced the formula for temperature detection. An AD7705 is used as an analog-to-digital converter, and a microcontroller STC89C52 serves as the master controller to acquire temperature data from the A/D converter and to control the process of heating the cold finger. The temperature data sampled and calibrated by the microcontroller can be displayed in real time on an LCD, and sent to a PC through the RS232 serial port for display and storage. In addition, the paper gives the temperature-data processing algorithm and the scheme of calibration (for eliminating systematic errors). We have conducted two test experiments, in which power supplies of 20V and 18.5V are used in the heating circuit, respectively. The statistical analysis of the test data shows that the temperature of the EMCCD cold finger can be controlled in the vicinity of a given low temperature (i.e., -100℃) and the absolute error can be less than 0.006 8℃. These results show that the EMCCD cold finger, its supporting mechanism, the temperature control circuit, and the software are well designed, making the detection and control of the temperature of the system meeting the requirements for an astronomical CCD camera controller.