Taylor-Hobson Talyvel 4 - Page 2
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  1. #21
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    One of the cables from read head to display unit was missing a connector. For the next person who has to fix or make a Talyvel 4 cable, here's the details.


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  3. #22
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    I didn't realise that NiCd batteries were still available except for military applications!

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    Quote Originally Posted by Mark Rand View Post
    I didn't realise that NiCd batteries were still available.
    NiMh and Li batteries are so much better that NiCd batteries are only used for "legacy" applications. If I needed to replace these I would modify the charger circuit and install a pair of 3300mAh 8.4V NiMh packs intended for model airplanes. But the current NiCd batteries still work well, so no need for that yet. Possibly no need ever since I intend to use this only in my shop where I have electrical power.

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  6. #24
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    Here's what the display unit looks like (turned off, sorry).



    I spent some time this weekend going through the calibration procedure. The gain calibration requires shifting the angle by 300 seconds of arc, which is 1.454mm in one meter. I wanted to be able to do this in many steps of around 20 arcseconds so that I could also test the linearity. At first I did this using a small sine plate, but it was very time consuming to keep shifting the gage blocks and very fussy and error-prone, so eventually I bit the bullet and made this long sine bar out of a piece of 30 x 40mm extruded aluminum I had kicking around (4mm wall thickness):









    I glued a hardened ground 10mm pin into a machined slot on the left side and fixed a micrometer screw with an 8mm ball on the right side. The ball is glued into a turned recess in the non-rotating micrometer screw shank.



    The length between the contact points is 1 meter. So I can smoothly shift the angle from -300 to +300 arcsecs just by dialing the micrometer between -1.45 and +1.45mm of level. Each graduation of the micrometer (0.01mm) is about 2 seconds of arc.

    The error of the bar over the +-300 arcsec range is around 0.3%, dominated by the accuracy of the micrometer screw and my ability to read the markings. The other major source of error is the determination of the distance between the dowel pin and the contact point of the ball, but the error here is less than 1 mm, so below 0.1%.

    When I first got the meter the gain for head A was about 65% of the correct value and the gain for head B was about 89% of the correct value. With this setup I was easily able to set it within 1% of the correct value. I was also able to test the linearity and repeatabilty of the level, which are remarkable. Taylor Hobson claims that the errors are below 2% of reading + 0.2 arcsec, but I am finding the linearity is within about 1% over +-300 arcsecs. It also repeats rock solid within 0.1-0.2 arcsecs, something which I found very challenging with an autocollimator.

    A nice test is to line up read heads A and B on the sine bar, put the display in B-A mode, and then tilt the bar, checking that the display does not vary as the sine bar is moved. With the gains set correctly the display of B-A fluctuates in the +-0.2 arcsec range as A and B vary over the range from -30 arcsec to +30 arcsec.



    This verifies that one can use the differential mode to remove table tilt when doing surface plate mapping.

    Fantastic device!
    Last edited by ballen; 08-05-2019 at 02:58 PM.

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  8. #25
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    I'm going to continue extending this thread with info that might be useful to others with Talyvel4 meters. This post concerns the computer interface. The manual provides good detail of what is needed: a DB-25 (male) connector to DB-9 (female) serial port connector cable, set up as follows:

    Code:
    DB25 (Taylvel) end              DB9 (Computer) end
    
    BRAID --------------------------------- BRAID 
    
    RxD 2 --------------------------------- 3 TxD
    TxD 3 --------------------------------- 2 RxD
    DTR 6 --------------------------------- 8 CTS
    GND 7 --------------------------------- 5 GND
    
        18--|                           |-- 1 DCD
        25--|                           |-- 6 DSR
                                        |-- 7 RTS
    What the manual completely fails to mention (and I figured out after spending 20 minutes with a scope tracing the circuit and scratching my head) is the link shown on the bottom left above. On the DB-25 side pins 18 and 25 must be jumpered!! This is done to reduce power use: the computer interface circuits get their supply current via this jumper. This is not documented anywhere except on the schematics! So if you unplug the DB-25 side (or if the jumper is missing) then the computer interface circuitry remains unpowered and non-functional.

    Another important detail that the manual gets wrong concerns the "remote" contacts. After sending the unit an ASCI "X" character (ASCII decimal 88) the unit does NOT begin steadily transmitting values as the manual claims. Instead, after sending the "X" the unit stands by until you close the "remote" switch contacts. Then it transmits a single measurement value. Again, the only way to figure this out is to look at the latching circuit in the schematic.

    In gradient mode the format of the transmitted values is ("S" means "slope"):
    Code:
    S_A-0.029  (channel A)
    S_B+1.237  (channel B)
    S_D+2.234  (channel B-A)
    In arcseconds mode it is:
    Code:
    __A-234.5  (channel A)
    __B+023.7  (channel B)
    __D-123.4  (channel B-A)
    The underscores above "_" means an ASCII blank space character, and "D" is used to denote "difference".

    I think there is no way to change from A to B to D (B-A) mode under computer control but need to look at the schematics with this in mind.


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