[ATM] LWT setup questions

[Bernard Maugoust <maugoust@free.fr>]

Hi all,

I have started thinking about modifying my existing Foucault tester to allow
it to perform the lateral wire test as well. As it's got only 1-way motion
capability, I would opt for the crudest way to achieve the goal: modify the
slit/KE part to accomodate for the slit/wire and allow it to swing 90°, and
then turn the whole thing 90° to measure lateral movement of the wire.

Don't be shy to have a laugh at my dumbness if the answers are so obvious I
could not figure them out!!! Making the thing and testing the same mirror
both ways (Foucault and LWT) would show me all I guess.
Anyway, my questions re. this LWT are the following (I'd use Sixtests to
reduce data, at least until Foucault Test Analysis can cater for that too):

-  I understand that the slit source and the wire can be positioned in the
same plane, but can the wire be at the same time above and to the side of the
slit, say 5 to 10mm, without affecting the accuracy of the test?

- I assume they can they can be made to move laterally together (thus opting
for 'moving source' in Sixtests). Is that right?

- would the data fed into Sixtests (caustic/LWT duly ticked, of course) go
then so: y = radius of the mirror zone being measured, X = constant distance
of the slit/wire in/outside ROC (inside meaning negative value?), Y = actual
zone measurements, and X bias being the previously, and carefully, measured
actual ROC?

I'd go for taking readings across the whole diameter (using a pin stick), and
divide by 2 the sum of the pair related to the same zone.

Last point: as far as I can see from the examples in Sixtests, it seems that
the LWT requires a greater reading precision than the more conventional
Foucault, roughly a division by a factor of 4 of the total movement. Should I
invest in a comparator reading down to the micron rather than keep using my
current one limited to 0.01mm (0.0004")?

Thanks in advance for your advice and for pointing out any misunderstanding
of mine :-)

Bernard

-- 
Bernard Maugoust 3°59'E 44°28'N

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