An AT-type microcomputer with a resident 16-channel, 12-bit A/D board is used to measure and store signals from small (0.5mm. dia. x 3mm long), fast (20ms), glass-encapsulated thermistors. Each thermistor is purchased with a 2-point factory calibration and is used in a bridge circuit to condition the signal before acquisition by the computer. The calibration values for each thermistor are stored in a separate computer. The calibration values for each thermistor are stored in a separate calibration file and are loaded into the program when the program is started. The bridge circuit is designed to accommodate a tolerance of +/-20% in the nominal thermistor resistance and cover a range of 25 degrees C to 45 degrees C with 0.01 degrees C resolution. The circuit response (50Hz) is set to handle the fast response time of the thermistor when needed. Custom software controls the sample acquisition rate, filtering linearization, calibration, and storage of the signals, the A/D card is run in a """"""""background"""""""" mode for 30-second intervals, with the data transferred directly to a specified memory location. This mode of operation frees the CPU for processing the previous interval's data and allows uninterrupted, or continuous, data acquisition. After the first cycle, the memory location is switched and another cycle started. The program then downloads the 16-channel data from the previous memory location and determines the resistance of each thermistor from the voltage readings. From this resistance and the calibration values, the temperature of each thermistor is calculated. The """"""""background"""""""" operation also allows updating or changing the calibration values (new thermistor) or relocating the thermistor (channel change) without interrupting the data acquisition.
