June 12, 2006: For the past couple weeks I have been experimenting with our led boards
as well as our photmultiplier tube in order to get a good understanding for what our signals should look like.
So far I have been able to view signals for single photo-electrons. By calculating the area under the curves
in the output signal produced by these single photo-electrons we are able to make a good estimate as to how
many photo-electrons are present when viewing signals produced by our led system. Originally, I looked at the
signals of the PMT's where I produced the TTL inputs, 5+/-, and gnd with function generators instead of the
power supply through the driver board which we will actually be using. When I looked at the signals using the
function generator there were two peaks that occured after the original pulse signal. Eventually after looking at several
screen shots, I determined that this was a flaw induced by the setup using the function generator and not
a problem inherent in our led design. I was able to make this assertion becuase when the led board was disconnected
from the function generator setup the two strange peaks were still visible (although more distorted). Also, when
I created the setup we will be using (power supply-->driver board-->led board), the peaks were not present.
June 13, 2006:
These are the three screen shots of single photo-electrons that I used to get an idea of the area under the pulse, which is then used to determine how many photo-electrons are present in larger pulses.
Here are screen shots which illustrate the double peaks following the initial pulse as mentioned above.
function generaor with led board
function generator no led board
Power supply with driver board 1
function generator with led board
June 15, 2006: Today was spent looking at how the peak voltage of the
PMT signal varied with the frequency of the input pulse. I adjusted the frequency of the pulse through a range
from zero to about 45 kilohertz. After takng several data points in this region, I recorded and plotted them in
excel. The voltages appear to fall off linearly as frequency is increased. Once I was able to see these results
I adjusted the pots to get a larger voltage signal. I then repeated the frequency-voltage measurements recorded the
results and plotted them in excel. Expectedly, the voltage decreased linearly with increasing frequency as it did
previously; the only difference is that the slope of the line changed. One suprising result of these trends is that
an increase in voltage by adjusting the potentiometers had virtually no effect on the maximum frequency at which
the led would produce a signal.