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7J20: Difference between revisions
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The '''Tektronix 7J20''', which only appears in the 1975 catalog, is a "rapid scan" optical spectrometer for the 250 nm to 1100 nm region. | The '''Tektronix 7J20''', which only appears in the 1975 catalog, | ||
Rapid scan means that it can capture the spectrum quickly enough to show spectral changes at temporal resolution of a few milliseconds. | is a "rapid scan" optical spectrometer for the 250 nm to 1100 nm region. | ||
Rapid scan means that it can capture the spectrum quickly enough | |||
to show spectral changes at temporal resolution of a few milliseconds. | |||
The instrument is based on a [https://en.wikipedia.org/wiki/Monochromator Czerny-Turner Monochromator], | The instrument is based on a [https://en.wikipedia.org/wiki/Monochromator Czerny-Turner Monochromator], | ||
in essence a narrow slit followed by a [https://en.wikipedia.org/wiki/Diffraction_grating diffraction grating]. | in essence a narrow slit followed by a [https://en.wikipedia.org/wiki/Diffraction_grating diffraction grating]. | ||
A [https://en.wikipedia.org/wiki/Vidicon vidicon tube] scans the optical spectrum and produces a periodic electric signal which is then displayed by the scope mainframe. | A [https://en.wikipedia.org/wiki/Vidicon vidicon tube] scans the optical spectrum | ||
and produces a periodic electric signal which is then displayed by the scope mainframe. | |||
[[File:7J20-principle.jpg | thumb | 400px | center | Operating principle (click to enlarge) ]] | [[File:7J20-principle.jpg | thumb | 400px | center | Operating principle (click to enlarge) ]] | ||
The spectrometer is packaged in two enclosures linked by an umbilical cable. | The spectrometer is packaged in two enclosures linked by an umbilical cable. | ||
The 7J20 is a 2-wide plug-in for [[7000-series scopes]] containing the sweep timing and mainframe interface circuits. | |||
The external enclosure is labeled "J20". | |||
It has controls for the optical components (grating, filters etc.) on one side and an input aperture on the other. | |||
The internal vidicon horizontal scan voltage corresponds to wavelength, | |||
but not in a linear way. | |||
To provide a linear nm/div horizontal display on the 7000-series mainframe, | |||
the vidicon horizontal scan signal is passed through a function generator IC, | |||
the [[155-0106-00]], | |||
which implements an interpolated lookup table. | |||
Inside the 7J20, there are 40 trimmer potentiometers that allow the lookup function to be tweaked | |||
so that the horizontal scale of the system is accurate. | |||
The 7J20 is very rare. According to Dennis Tillman, ''Best estimate is ~40 were actually built.'' | The 7J20 is very rare. According to Dennis Tillman, ''Best estimate is ~40 were actually built.'' | ||