a tiny servo motor and re: killing those darn germs
Posted by
Elliot Burke
on 2001-05-01 02:21:29 UTC
You're right, it is the 253.7 nm mercury line which is the strong one. In a
low pressure arc particularly this line is efficient in converting
electricity to UV radiation. This is why Cooper-Hewitt bulbs (fluorescent
lamps) are so efficient. In a high pressure arc its efficiency (253.7 nm
line) appears to be lower but radiance (brightness) is larger.
There is also a strong 184.9 nm line. This one will make ozone. A good
grade of quartz will transmit this wavelength, although most lamps have
envelope that do not (by design) transmit this wavelength. Also good for
disinfection, by using the ozone.
What the heck, mercury itself was used as a germicidal agent for centuries.
Probably best to keep it way from cutting fluids.
There was a technology described a few years ago where a TiO2 layer
(powder?) would be "activiated" by UV and be germicidal for long periods of
time. Has anyone heard anything about this?
The tiny motor is from a hard drive. The motor is a voice coil sort of
thing, with a ball bearing to constrain motion to an arc. I'm going to use
it to drive the reference mirror in an interferometer.
The problem is, my desired sensitivity of motion is 0.05 micron, and the
range of motion desired is about 5 mm. Since the motor position will be
linearly related to the current, current needs to be controled to about 10
ppm. Bandwidth can be pretty small, 100 Hz is OK. This is close to what a
16 bit DAC can theoretically do (2^-16 = 15 ppm), so that's where I'll
probably start.
Has anyone tried to use all the bits of a 16 bit DAC?
Can I use a cheap DAC card to get this sort of precision?
A really off the wall technique would be to synchronously modulate both
stereo outputs from a computer, run them into a differential amplifier to
drive the voice coil. If perfectly balanced the difference should be zero.
The degree of balance between the output levels could then by shifted (by
software) to generate different DC or low frequency output levels.
Any other ideas for making precision low frequency outputs from computer
control?
Plan B involves using a laser interferometer to measure the mirror position
and servoing the quadrature fringe signals.
BTW for those using laser diode for interferometers, a laser pointer makes a
dandy coherent source if you replace the button cells with AA or larger
batteries. The current capacity of the button cells isn't enough to make
the laser have a very narrow line, so the coherence length is quite limited.
The AA's do the trick. Values of frequency modulation of the laser with
current of 6 GHz/mA have been reported in the literature, so noise in the
power supply is not a good idea.
Elliot Burke
low pressure arc particularly this line is efficient in converting
electricity to UV radiation. This is why Cooper-Hewitt bulbs (fluorescent
lamps) are so efficient. In a high pressure arc its efficiency (253.7 nm
line) appears to be lower but radiance (brightness) is larger.
There is also a strong 184.9 nm line. This one will make ozone. A good
grade of quartz will transmit this wavelength, although most lamps have
envelope that do not (by design) transmit this wavelength. Also good for
disinfection, by using the ozone.
What the heck, mercury itself was used as a germicidal agent for centuries.
Probably best to keep it way from cutting fluids.
There was a technology described a few years ago where a TiO2 layer
(powder?) would be "activiated" by UV and be germicidal for long periods of
time. Has anyone heard anything about this?
The tiny motor is from a hard drive. The motor is a voice coil sort of
thing, with a ball bearing to constrain motion to an arc. I'm going to use
it to drive the reference mirror in an interferometer.
The problem is, my desired sensitivity of motion is 0.05 micron, and the
range of motion desired is about 5 mm. Since the motor position will be
linearly related to the current, current needs to be controled to about 10
ppm. Bandwidth can be pretty small, 100 Hz is OK. This is close to what a
16 bit DAC can theoretically do (2^-16 = 15 ppm), so that's where I'll
probably start.
Has anyone tried to use all the bits of a 16 bit DAC?
Can I use a cheap DAC card to get this sort of precision?
A really off the wall technique would be to synchronously modulate both
stereo outputs from a computer, run them into a differential amplifier to
drive the voice coil. If perfectly balanced the difference should be zero.
The degree of balance between the output levels could then by shifted (by
software) to generate different DC or low frequency output levels.
Any other ideas for making precision low frequency outputs from computer
control?
Plan B involves using a laser interferometer to measure the mirror position
and servoing the quadrature fringe signals.
BTW for those using laser diode for interferometers, a laser pointer makes a
dandy coherent source if you replace the button cells with AA or larger
batteries. The current capacity of the button cells isn't enough to make
the laser have a very narrow line, so the coherence length is quite limited.
The AA's do the trick. Values of frequency modulation of the laser with
current of 6 GHz/mA have been reported in the literature, so noise in the
power supply is not a good idea.
Elliot Burke