In atomic spectrophotometers comprising a source of radiation characteristic of an element to be detected in a sample, a monochromator for selecting a desired spectral line from radiation received from the source by the sample, and a detector for producing an output signal from the monochromator output radiation, the monochromator is accurately tuned to the desired line to obtain a maximum detector signal, and simultaneously, the gain of the detector is adjusted to keep the signal magnitude within the best working range of subsequent signal processing circuits. In accordance with the present invention, both adjustments are made simultaneously by comparing an amplified detector signal with a desired reference signal level corresponding to the best signal magnitude, and using the difference between them to adjust the gain of the amplified detector signal in a closed loop control system to continuously equalize the amplified detector signal with the reference level. The monochromator is tuned, preferably by an automatic device, to seek a minimum value of amplifier gain, at which the detector output will be a maximum at the peak of the spectral line with the amplified detector output being simultaneously equal to the desired reference level. The amplifier gain is then set to the values so obtained by a digital-analog converter, and absorption measurements are made with the control loop open.

A spectrophotometer wherein in order to set the instrument to a designated wavelength, the monochromator is first set to the designated wavelength position intended to be as such on the monochromator, and the entrance and exit slits of the monochromator are widened so as to measure a beam of light having a spectrum with an emission line at the designated wavelength, and the sensitivity of the light measuring circuit is so adjusted that the output therefrom is kept at a predetermined constant level, and then the slits are narrowed, whereupon wavelength scanning is conducted over a range of wavelengths including the designated wavelength so as to detect a peak in the emission line spectrum, and then the dispersing element is set to the detected peak position. A microcomputer controls the above operation in a sequential manner.

A spectrometer slit switching mechanism includes a slit plate having a plurality of entrance slits and exit slits formed at prescribed positions, parallel support rods for supporting the slit plate so as to be movable along the support rods, a screw portion formed on at least one support rod for transmitting forced to the slit plate, and a driving motor for transmitting rotational energy to the support rod provided with the screw portion, wherein the entrance slits are arranged on a line that runs parallel to the direction of movement of the slit plate and the exit slits are arranged on a line that is both parallel to and spaced a prescribed distance from the line on which the entrance slits are arranged. In accordance with this structure, the driving motor is operated in the clockwise and counterclockwise directions to raise and lower the slit plate in order to align a desired entrance slit and exit slit with the light path of the spectrometer. Also, after the desired slits have been positioned and the driving motor is stopped, the slit plate is prevented from moving downwards by the engagement of the slit plate with the screw portion of the support rod, and this eliminates the need for an excitation current to be supplied to the driving motor.

A device is provided which passes light of preselected wavelengths through a fluid or vapor to be tested. The light is detected after it has passed through the fluid or vapor. Upon detection, a voltage is created which is proportional in amplitude to the detected light strength for each wavelength of light. These voltages are compared to produce a ratio which represents the condition of the fluid or vapor which is tested. When the ratio is outside of preselected boundaries, control signals are generated which may trigger alarms or otherwise respond to the condition.

An optical scanning device, such as a chromatoscanner, includes a spectroscope having a rectangular outlet slit for producing a light beam in the shape thereof. A rotatable disk having a spiral slit is disposed in the path of the light beam to produce light pulses along radial lines of the disk which are directed to the surface of a specimen. The absorbancy of the light pulses at discrete positions of the specimen is measured and stored in a memory in accordance with the corresponding location on the specimen as derived from measuring the rotation angle of the disk.