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Output voltages
Submitted by freedmad on Wed, 07/14/2010 - 11:33
We printed out some metal oxide films and have been trying to scan them. The Scanstation is working fine. We made a sample with Fe,Co,Cu,Zn and there seems to be very little difference in the output voltages all the way across the slide. One thing I noticed that's seems odd is that the voltages on the txt file are around 11 and vary +/- 0.5 V. This seems awfully high considering that the initial output voltage dropped down to 1.8 before we started the scan. When I looked at some of the txt files in the experiments it looked like the voltages should start around the output voltage and go up or down from there. I think something is wrong, but I'm not sure what. Any suggestions? Dan F.
is this for - or + bias? I've
is this for - or + bias? I've been having problems with the + bias. I get a uniform image at 0.5v, but when i drop the bias down to 0.1v, the image becomes very clear.
Derek Rammelkamp
bias
We've tried it with both and got a uniform image. I'll try dropping the bias down. THanks!
Dan F.
Daniel A Freedman
update
While we were running a scan, I turned off the laser for a row and looked at the txt file and the voltages had dropped to something more normal (-0.5 or so). I believe at each point it takes the difference between the voltage with laser on/laser off? If that's right, it seems we're getting an unusually high photocurrent everywhere on the slide with the laser on. DF
Daniel A Freedman
I'm guessing you've already
I'm guessing you've already checked to see if the alligator clip is wet, or if all your connections are secure. All of my txt files have values between the range of 3 to 5, 11 seems high. I would think lowering the bias should help. I've been getting good images when the background color is orange for - bias and green for + bias, so around 2microA according to the scanstation. Whenever I get initial colors that are bright red for - and dark blue of + bias, I always end up with a uniform color and no image.
Derek Rammelkamp
We checked all of the
We checked all of the connections and everything seems fine. No matter where we set the bias, either positive or negative, we get a large, positive output photocurrent. Even with the bias set at 0 V, the photocurrent is still well over 5. The only thing we can think of is that there is something wrong with the box. Jenny??????????
Daniel A Freedman
We've been experiencing
We've been experiencing almost the same problem. Every positive scan we have run has always produced a uniform background. It doesn't matter what we set the bias to either. However, our negative scans work just fine. We think it might be a grounding problem with the box. But it's been bubble nitrogen through the electrolyte for ten minutes before the scan and then run nitrogen over the the electrolyte during the scan. We haven't tried that yet, but it might help.
Michael Albano
Albion College
MAA
What kind of photocurrents do
What kind of photocurrents do you get with the negative scans? One of things that I think points to a problem with the box is that even with a negative bias, our photocurrents end up being positive.
Dan
Daniel A Freedman
About a week ago: with the
About a week ago: with the negative scans we were getting a negative current about -3 to -5V with a bias
of 0.5. And with the positive scans we were getting a negative current as well about
-0.5 to -1V with a bias of 0.5.
So we took a look at the circuit board and electrical schematic to try and pinpoint where something was going wrong. We ended up replacing the chips because we thought that they might have blown.
After replacing the chips: we get a voltage between -1 and -3V with a bias of 0.5V for the negative scan.
And a voltage of +1 to +3V for a positive scan with a bias of 0.5V, but we are
still getting a uniform background for the positive
So we haven't fixed the problem yet which leads us to believe there might be a grounding problem which would explain the blown chips.
MAA
Where did you find the
Where did you find the electrical schematic?
We're going to try and check
We're going to try and check the power supply tomorrow. I noticed that the dark current spikes when you turn the laser on. A friend who, unlike me, knows something about electronics is worrying about the power supply being able to keep up with the change in load when the laser switches on and off.
DF
Daniel A Freedman
Output Voltages
Hello!
Earlier in the year we were also having a lot of similar problems with our box. The positive test provided good results but when we tried to test the same slides but with a negative bias, the scan malfunctioned and showed the plate as all one color. We figured that it was a problem with the hardware in the box itself and have simply been scanning our plates with the positive test only.
The Caltech/Polytechnic SHArK team
Polytechnic School
Has this issue been resolved?
Did anyone resolve this issue? I am having a similar problem; a consistently large photo current. I have run numerous scans with the bias (V) set at various values ranging between 0.5 and -0.5 at positive and negative, only to get the same result: a solid blue image.
I looked at the .txt file for the last scan (negative bias -0.1 (V). The numbers range from 6.7 to 6.9 when the laser hit 'blank' space, and between 0.0116 to 0.277 when the laser hit metal oxide solution(s).
Any current information would be greatly appreciated.
-Jason.
We fixed the problem by
We fixed the problem by separating the circuit that pulses the laser from the circuit that generates the bias voltage and measures the output current.
DF
Daniel A Freedman
auto scale?
Jason - Do you have your software set to autoscale? If you right click on the color scale bar - choose Auto Scale and that might help.