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The X381 is an experimental 560-series timebase plug-in, probably made in the early 1970s. | {{Plugin Sidebar | ||
It appears to have used a [[3B1]] plug-in as a starting point. | |manufacturer=Tektronix | ||
It was probably developed by [[Hiro Moriyasu]]. | |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 | No documentation is available for the X381, so everything in this page is just a guess based on examining the one existing plug-in. | ||
so everything in this page is just a guess | |||
based on examining the one existing plug-in. | |||
==Features== | ==Features== | ||
Line 18: | Line 28: | ||
==Principle of Operation (a guess)== | ==Principle of Operation (a guess)== | ||
The rotational position of the vernier sweep speed knob is linked by shafts and gears | The rotational position of the vernier sweep speed knob is linked by shafts and gears to the rotational position of the main encoder shaft. | ||
to the rotational position of the main encoder shaft. Attached to directly to the main encoder shaft are: | Attached to directly to the main encoder shaft are: | ||
* a rotary optical encoder, and | * a rotary optical encoder, and | ||
* a free-rotating (no angular stop) precision potentiometer | * a free-rotating (no angular stop) precision potentiometer | ||
Each angular position of the main encoder shaft produces a distinct pattern | Each angular position of the main encoder shaft produces a distinct pattern of illuminated or not-illuminated in the 26 | ||
of illuminated or not-illuminated in the 26 optical fibers (or flexible light pipes) | optical fibers (or flexible light pipes) that exit the rotary optical encoder. | ||
that exit the rotary optical encoder. These are optical signals are converted to electrical signals | These are optical signals are converted to electrical signals and the electrical signals are fed to the nixie controller ICs. | ||
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. | 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. | The rotary optical encoder produces two encodings at each rotational position. | ||
One encoding is in terms of TIME/DIV. | 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 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 | 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. | Meanwhile, a precision potentiometer is attached to the main encoder shaft. | ||
This potentiometer functions in essentially the same way as the vernier sweep speed | This potentiometer functions in essentially the same way as the vernier sweep speed on a conventional timebase plug-in such as a [[3B1]]. | ||
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. | 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, | When the rotary optical encoder is at the end of a revolution, an optical signal (one track on the encoder disk) | ||
an optical signal (one track on the encoder disk) calls for a step of | calls for a step of the 1-2-5 rotary sweep speed switch that is concentric with the vernier sweep speed knob. | ||
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. | A motor and gears rotate the rotary switch. | ||
The position of the main encoder shaft (and corresponding pattern of fiber illumination) | 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. | ||
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. | ||
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. | 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; | A pair of microswitches is attached to the vernier knob. One closes on clockwise torque; the other microswitch closes on counterclockwise 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. | ||
The direction of the torque of the vernier knob determines the direction of the step of the 1-2-5 | 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. | ||
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. | However, unlike a counter, the units of the vernier are proportional to the position of the 1-2-5 switch. | ||
==Rotary Optical Encoder== | ==Rotary Optical Encoder== | ||
Within the X381, | Within the X381, there is an octagonal aluminum enclosure containing a backlit disk of film that is rotated by a front panel knob. | ||
there is an octagonal aluminum enclosure containing a backlit disk of film | The disk functions similarly to a quadrature optical encoder, but instead of generating just two signals, it generates several signals. | ||
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. | There are pairs of human-readable numbers on the disk at each rotational position. | ||
These numbers are visible outside of the enclosure. | These numbers are visible outside of the enclosure. | ||
Each pair of numbers, when multiplied, gives a product very close to 10,000. | Each pair of numbers, when multiplied, gives a product very close to 10,000. | ||
Since the two numbers have a reciprocal relationship, | Since the two numbers have a reciprocal relationship, one number probably represents the sweep speed in time per division | ||
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. | ||
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]] | [[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]] | ||
Line 75: | Line 72: | ||
(Colored lines added to emphasize the three-way interleaving.) | (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. | |||
The bulb used for illuminating the encoder wheel is marked "6.3V" and has an integral lens | |||
Two of these bulb are used, side by side. | 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, | 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. | e.g., the "SEC"-mode numeric encodings versus the "Hz"-mode numeric encodings. | ||
Each photodetector has two strands of optical fiber entering it, | Each photodetector has two strands of optical fiber entering it, from separate tracks on the encoder disk. | ||
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. | ||
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. | 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, | 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. | ||
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. | ||
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. | The SEC/Hz switch is second from the bottom, with blue plastic wafers. | ||
Line 99: | Line 90: | ||
===Outer Knob=== | ===Outer Knob=== | ||
The outer knob is the coarse TIME/DIV control, | The outer knob is the coarse TIME/DIV control, and goes in 1-2-5 steps from 2 sec/div to 1 μs/div. | ||
and goes in 1-2-5 steps from 2 sec/div to 1 μs/div. | |||
The front panel knob rotates this rotary switch. | The front panel knob rotates this rotary switch. | ||
However, the switch can also be controlled by a motor in the plug-in. | 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, | 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 motor's gear is mechanically disengaged from the rotary switch shaft. | |||
The rotary coarse TIME/DIV switch controls the rightmost nixie tube, | The rotary coarse TIME/DIV switch controls the rightmost nixie tube, which shows the TIME/DIV units. | ||
which shows the TIME/DIV units. | |||
===Inner Knob=== | ===Inner Knob=== | ||
Line 114: | Line 102: | ||
Each radial position of the disk produces a pattern of light/dark in the light pipes coming out of the disk. | 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. | The patterns encode vernier TIME/DIV values. | ||
Each light pipe goes to a photosensor, which controls the left three decimal nixie tube. | 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, | 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. | ||
but is also motor-controlled, possibly to enable automated measurement. | |||
==Photos== | ==Photos== |