August 20, 2005
They don't make them like they used to- this thing is seriously heavy. I think it flattened the ball bearings in the moving cart.
I do not even have a table to lay it on since I am afraid it will crush a regular desk.
My list of things to do:
1) find out if it scans,
2) find out if the beamsplitter is fogged,
3) splice the high voltage connections for the HeNe laser back together (they got cut in the move),
4) get a table to put it on, and
5) see if I can rip the power supply for the mirror and HeNe laser out and put it in a smaller home-made housing.
October 13, 2005
I still have not turned it on yet since I do not have running air/water.
I decided to leave the power supplies in the housing for the time being- I might be able to find a table that the housing
will slide under as is. Otherwise if I do have to rip them out they will come out easily since it is rack mounted but I do not
have a rack to put them on, so anyway they are staying where they are for now. A lot of dust got into the instrument since I moved it here.
I must have left the shutter for the measurement beam open accidentally and now the first bounce mirrors
next to the sample compartment are pretty dusty.
November 3, 2005
OK so I have a new lab space now and it has water so I should be able to turn it on soon but the only problem is it will not fit on the standard
bench top without overhanging more than I think is a very good idea.
January 10, 2006
I traded some emails with George Rossman at Caltech who had one of the same FTIR's that I am working on. He was good enough to look
up some technical information for me like the inlet pressure for the moving mirror. I also asked if he had the old beamsplitter and I have not gotten
any answer on that yet.
February 1, 2006
I found a table for the FTIR and hooked up the gas and water connections. I also spliced the high voltage connection for the He-Ne laser back together.
April 25, 2006
I purchased a National Instruments PCI 5922 data collection card. It can collect data as fast as 67 ns and has a variable number of bits of resolution-
it can be as high as 24 bits, which is plenty of data points. It has 32 Mb of memory which corresponds to about 3.2 seconds worth of 100 ns time slices.
It has 2 channels so that the HeNe and the IR signals can be collected continuously when the mirror is scanning constantly, which is necessary for
keeping the instrument aligned. When it is actually to collect step-scan spectra the HeNe signal and the FTIR data can be collected sequentially on one channel.
June 8, 2006
OK I am really getting started now. I tried to turn it on today. Here is what I saw.
1) The high voltage cable that I spliced back together was making a very unsettling buzzing noise and I immediately turned the high voltage off. I am
going to try to splice it again but if it gives me any more trouble I should probably buy a new head and power supply since the head itself probably has to
be replaced anyway.
2) Both light sources, IR and visible, lit up. The current setup with the mirrors has the IR running into the interferometer which is good for me since I am
not going to figure how to get the stepper motors to flip back and forth.
3) The interferometer did not scan. I checked all the connections and confirmed that the power was not coming out of the power supply on that plug. This
voltage may need a signal from the defunct computer to turn it on. The good news is the indicator lights on the face of the power supply include an
indicator for this coil and seems to say that it runs on 12 V. So I am thinking maybe I will be able to rig up a power supply. I have to figure out several
things, like how fast to modulate it when it scans continuously, and how to deliver tiny impulses to make it step.
June 11, 2006
I found a very cool and very cheap solution to get the voltage for the solenoid to be modulated. It is a small circuit sold for the general purpose of
controlling power supplies with signals that have very low power like ttl signals. It is $70 here.
June 14, 2006
I have done some productive thinking about how to get the interferometer to scan. The circuit I mentioned on June 11 would have to be part of a fairly
complex setup to havecomplete control over the mirror. I am still thinking about several aspects of that problem including: how to prevent drift of the
mirror from the center position, if it is possible to have a single power supply that will handle continuous scanning and step scanning. Today I found a
short-term solution to get the mirror to scan continuously. What I did was I connected the coil directly to a signal generator. Apparently the mirror
moves with so little friction that the load it presents can be handled by the signal generator acting as the power supply. So I hook it up and vary the
frequency and the moving mirror follows perfectly. I left it running for about an hour and it did not drift noticeably, or
at least not enough to make the mirror bottom out.
I also got the HeNe laser to go on even though I am still lacking in the extension cord that got cut in the move. I did it by taking the power cable out
of its normal routing and running it out of the top of the instrument right to the power supply. It was just able to reach the power supply and the laser went on.
June 19, 2006
I got some advice on splicing the high voltage line for the HeNe laser from Don Paul at Alltec. He sent this figure which was very helpful. The splice was soldered with a
round bead (no pointy edges sticking out) and I potted it in epoxy (RTV is also OK for this purpose). I just soldered the shield leads together
and wrapped electrical tape around them. The laser went on and there were no buzzing noises this time.
June 23, 2006 I looked for the HeNe signals today and found that they are present. With the mirror being driven by the signal generator I can take the analog signals right off
the front panel of the power supply. With the power to the mirror turned off there is an erratic interference pattern. I am thinking it must mean that the mirror is
not stable to within a few fringes. I found the signal coming out of the MCT, but I had no liquid N2 to cool the detector. I was trying to rig up some of the
electronics I have to create a small box function wave at a very low frequency to try to get the mirror to step but was not able find a way to do it.
June 26, 2006
I removed the beamsplitter autochanger today and got a look at the beamsplitter. The instrument is much nicer to look at without that big piece of clutter in there.
I cannot tell with my naked eye if it has become fogged or not. I also learned that it is held in place by air pressure. With the inlet pressure off it has room to wiggle
and it is held in place so tight it cannot move with the pressure on at all. I suppose the tuning of the instrument when it was originally made using the stepper motors
would just maximize after the BS was locked down. So I think it would be a good idea if I altered its mounting so that it can be manually adjusted and will not move
out of position when the air pressure goes off.
I was also trying to figure out why there are three HeNe laser related signals on the power supply when I think there should be two for quadrature detection. The signals
are labeled as side ref 1 side ref 2 and center I was also trying to understand how the HeNe signal travels through the interferometer since I see it below the level of the
BS but I also think it is supposed to go through the Ge hole in the BS which is in the center. I have not figured this out yet. Also, I had an idea today for stabilizing the
mirror during step scan measurements. I am going to look for pressure release valves that can be ttl triggered so I can bleed the pressure out of the bearing when the
mirror is supposed to be stopped and turn it back on when it moves.
June 27, 2006
Today I figured out that the HeNe output follows a different pathway than the IR signal. It is all below the level of the IR signal. There is a separate visible light
beamsplitter and the moving mirror is not circular it is like two fused circles with a small face on the bottom that reflects the HeNe signal. This means I can study
this signal without the beamsplitter even being in the instrument. So I took it out and put it in a desiccators. Before I put it away I disassembled it and measured
all the components. There are two optical flats one is transparent and the other is partially transparent with germanium on it. They both measure 75 mm diameter
and ~7-7.5 mm thick. The transparent one has some pencil writing on its edge that says it is a quarter waveplate.
July 6, 2006
I have been searching for a solenoid valve to switch the air supply to the bearing off and on. The idea is to stabilize the mirror during step scan collection by
cutting off the air. I was not able to find anything that just worked off a ttl trigger. The best I could do was a 3 way valve that operates at 6.0 V and takes a
little less than a watt to open the valve. It is very compact, and has nice small dead volume of ~500 microliters, and it is available with 1/16th inch ports that
fit the tubing inside the instrument. I am going to have to make some circuit to trigger it's power supply with a low power voltage signal. The one I settled on is
from www.ASCO.com. It is part# AL2306.
August 30, 2006
I got the ASCO valve and started fooling around with how to trigger it. The specifications for it say that it requires 6 V and ~1 watt of power to open it. I tried
opening it by applying 6 V in 100 ms pulses and it did not open. I did not measure how much current was flowing. I did this by placing an electronic switch inline with a 6 V volt
battery, but it did not have the range to go lower than ~1 Hz. The signal it produced was a crude all positive square wave.
September 20, 2006
I figured out how to drive the Asco valve to open and close today. I found a signal generator with a low impedance output. This wave then triggered the valve perfectly. The sound of the valve
opening and closing seems to vary regularly up to about 30 Hz then it changes its sound. I am guessing that at around 30 Hz it cannot quite fully open before it starts to be
closed again. This estimate seems like it is opening faster than the ~ 100 ms time I read in the technical specs. Therefore I think it is probably OK to run it at 10 Hz but that is
the fastest I should drive it if I want to be conservatively sure it is completely opening and closing. If I set the mirror drive at a low frequency like 0.1 Hz and the solenoid valve
at a higher frequency like 1 Hz I can see it step ~10 times in each direction.
December 8, 2006
I finally got around to installing the data collection board into the computer. I started to work on learning Labview. I managed to collect data from a signal generator using the board.