Abstract: A gas sensor which can be used for measuring a low concentration repeatedly, which has a quick response and which can be used for a long time with high stability is provided. The gas sensor comprises a solid electrolyte, a detecting electrode provided in contact with one of the surfaces of the solid electrolyte and exposed to a gas to be detected, a counter electrode, provided in contact with the other surface of the solid electrolyte, and lead wires to place an electric voltage across both electrodes or to take out electric signals, wherein an inactive substance which is hard to form a reaction product with the gas to be detected is used as a material to constitute both electrodes.

Abstract: A surface undulation inspection apparatus for detecting a defect of a fine undulation including a change of a gentle profile or the like on a suitable surface of a specimen to be inspected, wherein a patterning light source is opposed to an image pickup lens having a pin hole with a specimen interposed therebetween to pin-hole image pickup the patterning light source through the specimen to be inspected whereby a ray passing through the specimen to be inspected is specified as a principal ray, and a local surface undulation defect on the surface of the specimen is stressed and a defective part is specified.

Abstract: According to the present invention, there is provided a heterodyne interferometer comprising a laser oscilator, a frequency modulator which splits the laser beam into two beams and causes the beams to have different frequencies, a photodetector which composes both beams after at least one beam is reflected or transmitted by an object under test, and produces an interference signal from a composed laser beam, a frequency analyzer which reveals a Doppler frequency component of the interference signal, and an x-axis and y-axis fine movement command circuit and a photodetector positioning mechanism which detects the amplitude of the a.c.(alternating current) component of the interference signal and positions the photodetector so that the amplitude is maximum.

Abstract: A screw surface flaw inspection method and an apparatus therefor, which projects light onto the surface of a screw, the light being scanned axially of the screw, and a detector which picks up the reflected light from the projected surface and sends an output signal to a signal processing circuit to thereby detect the flaw on a basis of time base variation of the intensity of reflected light. The method and apparatus enables the inspection of minute flaws rapidly and exactly.