NPB 100L Laboratory We will use several different kinds of apparatus in this lab some of which we will use many times Four of these will be key to your success in the lab None are dangerous to you but several are quite fragile easily broken and VERY expensive to replace Equipment Learn to use them wisely and carefully Stereo Microscope The stereo microscope is a wonderful instrument that lets you see small things in three dimensions if you have roughly normal vision If you normally wear glasses keep them on when you use the microscope How to use it properly 0 Turn on the light 1 Adjust the interocular distance distance between the eyepieces to fit YOU Both of your eyes must see the object 2 Set the magnification to Lowest 2 Focus on an object 3 Adjust the diopter correction on the eyepiece by rotating knob connected to one of the two eyepieces This knob enables both eyes to focus on the same plane i e at the same depth If you are going to succeed with the laboratory work in NPB 100L you will need to be able to use these instruments effectively If you are not comfortable with the microscope take some time to adjust the interocular distance and diopter correction carefully and study some familiar object like a toothpick or pencil tip When you are working in a group be patient Each time you take over the microscope from another student adjust the interocular distance again and the diopter correction again If you don t you are liable to get headaches and make mistakes Do NOT pick up or attempt to move a microscope Ask your instructor to do it for you ATTENTION Page 1 of 9 TracerDAQ Pro and the A D converter box This combination of hardware the box with eight BNC jacks and a USB connector and software TracerDAQ Pro lets you record electrical signals to the computer There are no hardware adjustments for you to make except to connect your apparatus to the correct channels on the analog to digital A D box We will use two features of this software the Oscilloscope and the Strip Chart The oscilloscope The Oscilloscope screen looks like this The Oscilloscope displays recorded data as a plot of Voltage y axis as a function of Time x axis As many as four Channels can be plotted at once Each plot is referred to as a sweep The Channel settings and Timebase controls set the scale base of the Voltage y axis and Time x axis respectively These are very important because they determine the sensitivity of your measurements Note that the indicated settings reflect the voltage and time associated with a single rectangular division bordered by dotted lines in the oscilloscope screen not the entire window Thus for the example screen shown above the Time base is 1 ms per horizontal division so the entire screen width covers 10 horizontal divisions 1 ms per horizontal division 10 ms Similarly the voltage base channel setting is 5 V per vertical division for each of the recorded channels so the entire vertical extent of the screen covers 8 vertical divisions 5 V per division 40 V Page 2 of 9 To start a recording press the Run i e Play button To stop a recording press the Stop button Triggering The Trigger settings and Internal Trigger Level tell the Oscilloscope to pull the trigger to start recording when a specified criterion is met such as the voltage crossing upward or downward through a given value T0 They let you control when a sweep begins To set the value of voltage required to start a sweep adjust the T0 marker on the right of the graph to the appropriate value Then set the Internal trigger slope button to indicate whether triggering should occur when this T0 value is crossed in an upward direction or downward direction The T button itself toggles between three different Trigger modes Normal causes a sweep to occur whenever the trigger criterion is met Auto is like Normal except that it will automatically cause a sweep to occur if nothing has happened for a set period of time Single causes a sweep to occur only the first time the criterion is met after you start a recording and then stop the recording Note the event that caused the trigger will appear aligned underneath the triangle pointer that abuts the top of the oscilloscope graph Typically you will want this to be fairly far to the left e g all but 1 or 2 divisions to the left so that you can use most of the screen to see what happened after the triggering event but still leave a bit of room in case you want to see what occurred just before the triggering event Markers Markers let you measure voltage or time differences in your recordings You can change their orientation from vertical for measuring time to horizontal for measuring voltage using the Edit Display Markers menu the SET button or most easily by double clicking a marker If you place two horizontal markers at the bottom and top of a feature of a voltage trace e g the bottom and top of an action potential and click on a marker the screen will show you values of the voltage at each marker individually and most relevant the difference between these values Similarly one can place vertical markers at the start and end of a region of interest and get times and time differences between events the time difference also will appear on the top of the oscilloscope screen File menu The File menu has several important functions you will use including Save As and Print Page 3 of 9 Example recording Below is an example set of data from a recording in which two different voltage measurements were made simultaneously one on Channel 0 blue trace and one on Channel 1 black trace One sweep across the screen is shown The trigger was set up for Channel 0 which is why T0 and the arrowhead at the top of the graph are in blue The T0 arrowhead at the right shows the voltage level at which the trigger was set and the blue arrowhead indicates the time at which this voltage level was crossed by the blue trace POSTLAB QUESTION PL1 a What are the voltage base and time base for the Channel 0 example recording shown b Approximately to within 1 ms what is the amount of time between the two vertical above markers c Approximately to within 0 2 Volts what is the amplitude relative to the flat baseline level that occurs before the voltage goes sharply upward of the peak that occurs in the Channel 0 trace Page 4 of 9 The Strip Chart is a continuous recording of the voltage of up to 4 channels with each The Strip Chart recorder channel appearing within its own horizontal lane If you ve seen a seismograph needle recording