Lab manual

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Unformatted text preview: Windows Signing” answer “proceed anyways.” Once Data Studio and the driver are installed, unplug the PasPort interface, and reboot the system. With the system running (and you logged in), plug the PasPort interface, WITHOUT a sensor in it, into a USB port. Make sure the green light is on on the Pasport sensor front. Next, plug the probe you want into the PasPort interface; make sure the writing on the probe and the interface are in the same direction, and it should plug in smoothly. You system will recognize the sensor, and bring up a dialog screen asking you what you would like to do; choose “Launch DataStudio.” Once DataStudio is launched, it looks as if you should just be able to hit “start” and it will begin collecting data. Indeed, it would, but it might not be wha t you want it to do, so we must customize the software so it knows what we want it to do. Calibration of the System Many of the probes are pre-calibrated, however, there are times that we will want to calibrate them ourselves. The probes work by voltage; whatever they are measuring is converted into a voltage, which is read by the interface and fed to the computer. For example, the temperature probe has some given voltage that corresponds to a given temperature, and the factory calibration for this is relatively good. However, differences in manufacturing from one probe to the next means that there are small differences that might throw the sensor off a bit. For many experiments, these differences are not important and will usually cancel each other out; however, if we are doing a highly precise experiment where we need the absolute temperature (instead of the relative temperature), then we will want to calibrate the probe. Dakota State University Page 18 of 232 Using the Pasco System General Chemistry I and II Lab Manual To calibrate the probe, choose the “set-up” icon near the top of the display. There you will see a variety of choices in the new dialog screen; to calibrate the probe, choose “calibrate.” To perform a proper calibration, Pasco will typically ask you for two set points, a high set point and a low one. They assume that the system will act linearly; as a chemist, this kind of bothers me. I’ve learned a long time ago that a minimum of three points is necessary to assure linearity, but we will discuss this, as well. The set points can be done in one of two ways; either you can measure the value relative to a source that you trust more, or you can measure a fixed point. For example, for the temperature probe, we can use a high precision mercury thermometer in the lab to compare the values with Pasco, or we can use a well-known phenomenon like melting or boiling water. For the former, simply place the Pasco temperature probe and the thermometer into the same material (perhaps a beaker of water). Give both the probe and the thermometer a minute or so to equilibrate, and read the temperature as indicated by the thermometer. Type this value in for point 1 and click “set.” Notice that you will have to do this for two different temperatures; you can...
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This note was uploaded on 09/18/2012 for the course CHEMISTRY 1010 taught by Professor Kumar during the Fall '11 term at WPI.

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