A two-color pyrometer was developed for monitoring the surface temperature of metal chips formed during high-speed machining processes. Optical access to the tool-chip interface was obtained by cementing a plastic light pipe into a 1/16-in. (1.6-mm) hole milled through the carbide tool insert. The light pipe serves to transmit radiation falling on the rake face of the insert to radiation detectors located elsewhere. Radiation captured by the light pipe is passed through a lens-beam splitter combination and imaged on two identical photodiode detectors. The diodes have integral operational amplifiers to achieve high detectivity and low-noise operation. Each photodiode is masked by an interference type narrow-band filter having spectral bandpass frequencies chosen to match the point where the emittance of several metals is constant for all temperatures. Thus, the temperature of the chip stream monitored by the diodes is a function of the intensity measured for each spectral band at the same instant in time. The functional relationship between true temperature and the ratio of signal amplitudes (the calibration curve) was established for pyrometer over the interval 1000–1750 K using standard laboratory methods.

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