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{{Plugin Sidebar | |||
|manufacturer=Tektronix | |||
|series=560-series scopes | |||
|type=X381 | |||
|summary=Experimental timebase plug-in | |||
|image=Tek x381 front.jpg | |||
|caption=Tek X381 front | |||
|introduced=(not released) | |||
|discontinued=(n/a) | |||
|designers=Hiro Moriyasu | |||
|manuals= | |||
* n/a (not released) | |||
}} | |||
The '''Tektronix X381''' is an experimental 560-series timebase plug-in, probably made in the early 1970s. | |||
It appears to have used a [[3B1]] plug-in as a starting point. It was probably developed by [[Hiro Moriyasu]]. | |||
No documentation is available for the X381, so everything in this page is just a guess based on examining the one existing plug-in. | |||
==Features== | |||
* Digital front-panel display of sweep rate in TIME/SEC or Hz. | |||
* Continuous vernier adjustment of sweep rate from the slowest rate to the fastest rate with no discontinuities. | |||
==Front Panel== | |||
The front panel has: | |||
* a Nixie display which is driven by a [[Fairchild 9960]] decoder/driver IC. | |||
* a two-position slide switch with positions marked "SEC" and "Hz". | |||
* a TIME/DIV knob concentric with a vernier sweep speed knob. | |||
==Principle of Operation (a guess)== | |||
The rotational position of the vernier sweep speed knob is linked by shafts and gears to the rotational position of the main encoder shaft. | |||
Attached to directly to the main encoder shaft are: | |||
* a rotary optical encoder, and | |||
* a free-rotating (no angular stop) precision potentiometer | |||
Each angular position of the main encoder shaft produces a distinct pattern of illuminated or not-illuminated in the 26 | |||
optical fibers (or flexible light pipes) that exit the rotary optical encoder. | |||
These are optical signals are converted to electrical signals and the electrical signals are fed to the nixie controller ICs. | |||
Thus, as the vernier sweep speed knob is rotated, the digital display on the front panel follows it. | |||
The rotary optical encoder produces two encodings at each rotational position. | |||
One encoding is in terms of TIME/DIV. | |||
The other encoding is in terms of Hz of a waveform that repeats within a given number of horizontal divisions, e.g., 10 divisions. | |||
The appropriate encoding is selected based on the position of the front panel SEC/Hz two-position switch. | |||
Meanwhile, a precision potentiometer is attached to the main encoder shaft. | |||
This potentiometer functions in essentially the same way as the vernier sweep speed on a conventional timebase plug-in such as a [[3B1]]. | |||
The function of this potentiometer is not affected by the position of the front panel SEC/Hz two-position switch. | |||
When the rotary optical encoder is at the end of a revolution, an optical signal (one track on the encoder disk) | |||
calls for a step of the 1-2-5 rotary sweep speed switch that is concentric with the vernier sweep speed knob. | |||
A motor and gears rotate the rotary switch. | |||
The position of the main encoder shaft (and corresponding pattern of fiber illumination) is insufficient to disambiguate which direction to rotate the 1-2-5 sweep speed switch. | |||
One possible solution would be to use memory, i.e., to continue in the same direction as recent motion of the vernier knob. | |||
The approach taken in the X381 is to use a torque sensor in the vernier knob. | |||
A pair of microswitches is attached to the vernier knob. One closes on clockwise torque; the other microswitch closes on counterclockwise torque. | |||
The direction of the torque of the vernier knob determines the direction of the step of the 1-2-5 sweep speed switch. | |||
This forms an electromechanical counter, similar to an odometer, with the 1-2-5 switch accumulating a count of the rotations of the main encoder shaft. | |||
However, unlike a counter, the units of the vernier are proportional to the position of the 1-2-5 switch. | |||
==Rotary Optical Encoder== | |||
Within the X381, there is an octagonal aluminum enclosure containing a backlit disk of film that is rotated by a front panel knob. | |||
The disk functions similarly to a quadrature optical encoder, but instead of generating just two signals, it generates several signals. | |||
There are pairs of human-readable numbers on the disk at each rotational position. | |||
These numbers are visible outside of the enclosure. | |||
Each pair of numbers, when multiplied, gives a product very close to 10,000. | |||
Since the two numbers have a reciprocal relationship, one number probably represents the sweep speed in time per division | |||
while the other number represents the sweep speed in frequency, e.g., of a waveform that repeats in one horizontal division. | |||
[[File:Tek x381 disk numbers colored.jpg|300px|Tektronix X381 optical encoder values are an interleaving of three sequences, each in increments of 1.5% per step]] | |||
Tektronix X381 optical encoder values are an interleaving of three sequences, each in increments of approximately 1.5% per step. | |||
(Colored lines added to emphasize the three-way interleaving.) | |||
The bulb used for illuminating the encoder wheel is marked "6.3V" and has an integral lens, see photo below. | |||
Two of these bulb are used, side by side. | |||
It is possible that they are energized independently to select different tracks on the encoder disk, | |||
e.g., the "SEC"-mode numeric encodings versus the "Hz"-mode numeric encodings. | |||
Each photodetector has two strands of optical fiber entering it, from separate tracks on the encoder disk. | |||
It is possible that the position of the SEC/Hz knob determines which of the two bulbs will be energized, thus selecting one or another subset of the tracks on the encoder disk. | |||
Feeding pairs of fiber strands into a single photodetector serves as a logical OR. | |||
Viewed from a modern perspective, the encoder disk is two ROMs driven by the same address lines, with the two light bulbs serving as chip select lines. | |||
However, the wiring on the SEC/Hz switch suggests that there's more complexity than just selecting between two light bulbs. | |||
The SEC/Hz switch is second from the bottom, with blue plastic wafers. | |||
[[File:Tek x381 lower front left.jpg|300px]] | |||
==Motorized TIME/DIV== | |||
The TIME/DIV control is two concentric knobs. | |||
===Outer Knob=== | |||
The outer knob is the coarse TIME/DIV control, and goes in 1-2-5 steps from 2 sec/div to 1 μs/div. | |||
The front panel knob rotates this rotary switch. | |||
However, the switch can also be controlled by a motor in the plug-in. | |||
When the coarse TIME/DIV control is rotated using the front panel knob, the motor's gear is mechanically disengaged from the rotary switch shaft. | |||
The rotary coarse TIME/DIV switch controls the rightmost nixie tube, which shows the TIME/DIV units. | |||
===Inner Knob=== | |||
The inner knob is probably a vernier TIME/DIV control. | |||
The inner knob rotates the optical disk and a precision rotary potentiometer, Tektronix part number [[311-0537-01]]. | |||
Each radial position of the disk produces a pattern of light/dark in the light pipes coming out of the disk. | |||
The patterns encode vernier TIME/DIV values. | |||
Each light pipe goes to a photosensor, which controls the left three decimal nixie tube. | |||
The inner knob, like the outer knob, can be rotated by turning the front-panel knob, but is also motor-controlled, possibly to enable automated measurement. | |||
==Photos== | |||
<gallery> | <gallery> | ||
Tek x381 front.jpg | |||
Tek x381 1.jpg | Tek x381 1.jpg | ||
Tek x381 2.jpg | Tek x381 2.jpg | ||
Line 5: | Line 114: | ||
Tek x381 5.jpg | Tek x381 5.jpg | ||
Tek x381 6.jpg | Tek x381 6.jpg | ||
Tek x381 wheel1.jpg|backlit with flashlight for photo | |||
Tek x381 wheel2.jpg|backlit with flashlight for photo | |||
Tek x381 nixies.jpg | |||
Tek x381 encoder lamp.jpg|Bulb used for illuminating the encoder disk. | |||
</gallery> | |||
==Photos of Optical Disk== | |||
<gallery> | |||
Tek x381 disk numbers 1.jpg | |||
Tek x381 disk numbers 2.jpg | |||
Tek x381 disk numbers 3.jpg | |||
Tek x381 disk numbers 4.jpg | |||
Tek x381 disk numbers 5.jpg | |||
Tek x381 disk numbers 6.jpg | |||
Tek x381 disk numbers 7.jpg | |||
Tek x381 disk numbers 8.jpg | |||
Tek x381 disk numbers 9.jpg | |||
Tek x381 disk numbers 10.jpg | |||
Tek x381 disk numbers 11.jpg | |||
Tek x381 disk numbers 12.jpg | |||
Tek x381 disk numbers 13.jpg | |||
Tek x381 disk numbers 14.jpg | |||
Tek x381 disk numbers 15.jpg | |||
Tek x381 disk numbers 16.jpg | |||
Tek x381 disk numbers 17.jpg | |||
Tek x381 disk numbers 18.jpg | |||
Tek x381 disk numbers 19.jpg | |||
</gallery> | </gallery> | ||
[[Category:560 series plugins]] | [[Category:560 series plugins]] | ||
[[Category:Prototypes]] | [[Category:Prototypes]] |