Gravity has been verified!
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Posts: 46,084
12/11
Tracy, Allen, Chris, Steve: First a couple of corrections: 1ST )the
slot width was .22 inches (not .25inches)… 2nd ) the velocity at 30
in. was 107.7 in/sec not the 115 in/sec quoted yesterday (this would
have been the velocity at 34 inches, not 30 inches).
Yes I do have a voltmeter and have verified that the circuit changes
from 0.3 volts at "dark" (between slots) and a full 5 volts at "light"
(between the slot). This was verified as soon as the circuit was
constructed. My circuit is very simple, it consists of two variable
resistors for the voltage divider and an OPTEK optical switch (OPB625
I think, I'm at work and don't have the data sheet). There are no
other components to "slow down" the system. From a plot of the input
requirements for the photo sensor, I chose 1.20V at 10 milliamps to
turn operate the sensor (I kept the 500 ohm total resistance for R1
and R2 to obtain the 10 mamp requirement but had to play with the
resistor ratios a little ensure the 1.20V with the optical sensor
tapped off the 2nd resistor. I started off with 380 and 120 ohms but
I think I ended up with 320 for R1 and 180 for R2 to obtain the 1.20 V
with the optical sensor in the circuit). At the slots I got a full 5
volts and between the slots (dark) I got 0.3 volts. The circuit was
verified to operate properly by sliding the slotted strip back and
forth and measuring the voltage at the input pin (pin 7). So I knew 2
weeks ago that the circuit was working. But I needed to know that the
data would be "properly" (accurately) counted (timed) and x-ferred
within the bounds of the experiment. That's when I thought I would
use the gravity experiment as a calibration method. I'm pretty sure
that the actual experiment will be much less "taxing" on the
capabilities of the stamp than the calibration set-up. I'm expecting
the maximum rpm to be less than 2000 rpm (actually I'm expecting it to
be closer to 1000 rpm but I want to be sure I can handle the higher
rpm if necessary). This will translate to a tangential velocity of
approx. 43 in/sec. on Katie's 3 inch diameter disc (1.5 inch radius
less the .2 inches where the slot is located). The "calculated"
gravity calibration velocities ranged from 27.7 in/sec to 107.7
in/sec. at 2 inches and 30 inches respectively (the 115 in/sec quoted
yesterday would have been at 34 inches but I only checked to 30
inches.) Don't know what the difference in calculations are? I used
g=Dv/Dt ; v=Dx/Dt ; g=Dx/Dt2 ; t=[noparse][[/noparse]Dx/g]1/2 I think my calculations are
correct but I may have punched in a number wrong?
At any rate, using the hex output format, I did get good values for
gravity (an average of 388 in/sec2 for the 1st 5 data points instead
of the 386 in/sec2 of true gravity) this accuracy tailed off over the
remaining 10 measurements for a total average of 368 in/sec2. I'm
happy with the average of the 1st 5 data points though since the
expected velocities will be significantly less than the velocities
actually calibrated over. I repeated the experiment three times with
almost identical averages all three times. GRAVITY HAS BEEN VERIFIED!
I'm hoping I'm finished with the data acquisition system and Katie can
now start her experiment of making her Inertial Dynomometer. ONE
LAST QUESTION: I think you said the data could be x-ferred fastest
using ASCII?? Is this true?
I certainly want to thank everyone that helped out, your comments and
inputs were (are) certainly appreciated. I've never constructed a
circuit before or used a BS2 and haven't programmed anything since
1984 when I was in school. So I certainly couldn't have done it
without your help. THANK YOU ALL VERY MUCH. Mike Galbreath
Tracy, Allen, Chris, Steve: First a couple of corrections: 1ST )the
slot width was .22 inches (not .25inches)… 2nd ) the velocity at 30
in. was 107.7 in/sec not the 115 in/sec quoted yesterday (this would
have been the velocity at 34 inches, not 30 inches).
Yes I do have a voltmeter and have verified that the circuit changes
from 0.3 volts at "dark" (between slots) and a full 5 volts at "light"
(between the slot). This was verified as soon as the circuit was
constructed. My circuit is very simple, it consists of two variable
resistors for the voltage divider and an OPTEK optical switch (OPB625
I think, I'm at work and don't have the data sheet). There are no
other components to "slow down" the system. From a plot of the input
requirements for the photo sensor, I chose 1.20V at 10 milliamps to
turn operate the sensor (I kept the 500 ohm total resistance for R1
and R2 to obtain the 10 mamp requirement but had to play with the
resistor ratios a little ensure the 1.20V with the optical sensor
tapped off the 2nd resistor. I started off with 380 and 120 ohms but
I think I ended up with 320 for R1 and 180 for R2 to obtain the 1.20 V
with the optical sensor in the circuit). At the slots I got a full 5
volts and between the slots (dark) I got 0.3 volts. The circuit was
verified to operate properly by sliding the slotted strip back and
forth and measuring the voltage at the input pin (pin 7). So I knew 2
weeks ago that the circuit was working. But I needed to know that the
data would be "properly" (accurately) counted (timed) and x-ferred
within the bounds of the experiment. That's when I thought I would
use the gravity experiment as a calibration method. I'm pretty sure
that the actual experiment will be much less "taxing" on the
capabilities of the stamp than the calibration set-up. I'm expecting
the maximum rpm to be less than 2000 rpm (actually I'm expecting it to
be closer to 1000 rpm but I want to be sure I can handle the higher
rpm if necessary). This will translate to a tangential velocity of
approx. 43 in/sec. on Katie's 3 inch diameter disc (1.5 inch radius
less the .2 inches where the slot is located). The "calculated"
gravity calibration velocities ranged from 27.7 in/sec to 107.7
in/sec. at 2 inches and 30 inches respectively (the 115 in/sec quoted
yesterday would have been at 34 inches but I only checked to 30
inches.) Don't know what the difference in calculations are? I used
g=Dv/Dt ; v=Dx/Dt ; g=Dx/Dt2 ; t=[noparse][[/noparse]Dx/g]1/2 I think my calculations are
correct but I may have punched in a number wrong?
At any rate, using the hex output format, I did get good values for
gravity (an average of 388 in/sec2 for the 1st 5 data points instead
of the 386 in/sec2 of true gravity) this accuracy tailed off over the
remaining 10 measurements for a total average of 368 in/sec2. I'm
happy with the average of the 1st 5 data points though since the
expected velocities will be significantly less than the velocities
actually calibrated over. I repeated the experiment three times with
almost identical averages all three times. GRAVITY HAS BEEN VERIFIED!
I'm hoping I'm finished with the data acquisition system and Katie can
now start her experiment of making her Inertial Dynomometer. ONE
LAST QUESTION: I think you said the data could be x-ferred fastest
using ASCII?? Is this true?
I certainly want to thank everyone that helped out, your comments and
inputs were (are) certainly appreciated. I've never constructed a
circuit before or used a BS2 and haven't programmed anything since
1984 when I was in school. So I certainly couldn't have done it
without your help. THANK YOU ALL VERY MUCH. Mike Galbreath