2. Do research as required (add point form notes and add references for things that aren’t obvious, or may be useful to others interested in the area. It is very helpful to add equations and figures at this point.
We know from basic physics that acceleration is the second derivative of position. If we are dropping a small object near the surface of the earch gravity is nearly constant. If gravity is giving us a constant acceleration we can integrate this twice to get the following function for height.
3. Set up a Mathcad document that uses both of the methods for determining acceleration using equal sized time steps, and unequal time steps. Note: To do iterative calculations in Mathcad you can put the equations in a matrix, or write a script.
1. Set up a dry slope and slide a mass down it. A strobe light will be used to generate equal time divisions. Assign one person to release the mass, and three people to mark positions as the mass slides (on the first, second and third strobes). Measure the positions at each strobe and record. Use the Mathcad document to calculate acceleration.
2. Set up a dry slope and slide a mass down it. There will be three position sensors placed at equal distances (see figures below). The position sensors will be connected to a computer running LabVIEW. Release the mass and measure the times at which is passes the three points on the slope. Use the Mathcad document to calculate acceleration.
We need to observe how system behavior changes over time. To do this we can take successive readings and then plot them as a function of time. If we look at the screen of an oscilloscope, the horizontal axis represents time and the vertical axis voltage. One significant problem with any time based sampling device is when to start recording. We use certain settings to trigger the beginning of the beam scan. Each type of signal will require a different type of trigger, and so oscilloscopes have multiple settings to make them adaptable.
We will connect the lab oscilloscope to the computer with an interface card and cable. The interface between the computer and oscilloscope is called GPIB (General Purpose Instrument Bus) and is also known as IEEE-488. It is a networking scheme that will allow more than one device to be connected to the computer by using chains of cables. To interface to GPIB devices, we need a special interface card in the computer and interface software. We will use LabVIEW to communicate with the oscilloscope.
In general, an oscilloscope can sample voltages at rates from 0Hz up to about 1GHz. A typical inexpensive oscilloscope will sample data up to 10MHz. The DAQ card in the computer have the potential to sample up to 100KHz.
1. Before turning on the power to the oscilloscope, you must give it an address as a GPIB device. The address is a number XX set with dip switches. These are found on the side of the oscilloscope and switches 1, 6 and 8 should be set to "1". All others should be set to "0".
2. The oscilloscope is a very flexible device that can be reconfigured for various measurements. To set various parameters, we use the switches on the front panel, near the display. Set the switches on the front to match the descriptions below:
3. Now set up the power supply and connect it to the oscilloscope so that it will supply a signal. To do this, you need to connect the probe to the oscilloscope (CH1) and then to the positive and common terminals of the power supply.
4. You can now set up a signal to be measured. Turn on the power supply and then program it for 10V on the POS, and 0V on NEG supplies. The OUTPUT should be OFF. Finally, lock the program by pressing LOCK. You may now set up the scan trigger on the oscilloscope. Start the scope scanning continuously in the A TRIGGER mode by pressing P-P AUTO (on). Next you need to ’zero’ CH1. To do this, set the input to GND and use CH1 POSITION to center the trace. Once centered, change the input from GND to DC. The trace on the screen should now reflect the actual input. Set the scale to 2 VOLTS/DIV.