| 摘要 |
PURPOSE:To take a high-precision measurement while reducing an error in quantization accompanying digital conversion by adjusting a measurement signal to an invariably proper signal level and inputting the measurement signal to an A/D converter. CONSTITUTION:The detection signal of a photodetector 12 is inputted to a signal level adjusting circuit 40 and an input signal protecting circuit 42 through a linear DC amplifier 16 and a main amplifier 18 and amplified to a proper level. In this case, the level adjusting circuit 40 performs the switching of a multiplexer 48 under the control command of a CPU32 to input a signal of one of three stage levels to an A/D converter 24. Thus, even when the measurement signal becomes extremely low in level as a body to be measured increases in thickness, the signal level adjusting circuit 40 amplifies the signal to the proper level to reduce the error in quantization, measuring the thickness with high precision. |
