USING THE OSCILLOSCOPE
This is an outline to follow in using the oscilloscopes. Not all of the oscilloscopes are exactly the same. If you have any questions, please ask.
1. Plug the paddle into the scope. Remove all small (lemo) adapters or add a BNC (big) adaptor if you have a lemo connector at the end of your cable. The cables have a 50 Ω impedance internally. You must match this impedance when you terminate (end) the cable or the signal will reflect at the cable end.
· If your scope has a 50 Ω DC setting (under the VOLTS/DIV knob), simply plug in your signal cable.
· If your scope has a 1 M Ω DC setting, add a ‘T’ connector. Plug the signal cable into one end and a terminator into the other end as shown below.
· If your scope is not labeled, assume a 1 M Ω DC setting.
· These instructions assume you are plugging your signal cable into channel 1.
Signal Cable Terminator
2. Make sure the scope is set to the following levels. (Also, make sure all volts/div and time/div inner knobs are turned until locked into place.)
Ch.1 Ch. 2 Time Trigger
Mode Source Coupling
20 Mv/div Auto - Initially
Set to DC Coupled
This is a typical scope layout. Your scope may vary. (For example, “source” is often divided into multiple switches.
3. Turn the power on with the oscilloscope set up as in step 2. Set Trigger mode to “Auto” and source to Ch. 1. You should see a horizontal line. Adjust the Ch. 1 position and the time position if the line is not in the orientation as is drawn below.
4. Set the trigger mode to “Norm”. Adjust the level. As you turn the knob, you should see triggered light flash. This is slightly “Zero”. Turn the knob 1/8 of a turn counterclockwise from this point. (This sets a negative threshold.)
5. Connect the PMT to a signal cable. Set the high voltage to 1000 Volts. Adjust “level” until triggered light blinks frequently but is not always on. Look at the signal. The signal will be faint! Use a dark cloth or hands to shield room light. Turn the scope display intensity all the way up (clockwise). Ask for help if you see nothing or if you can’t get the triggered light to blink frequently.
6. Measure the size of the signal. You want ~100 mV from base to peak. Increase the high voltage slowly in 50 V increments. Remeasure the signal size. Do not exceed 1400 V without checking with Susen or Kevin. Record the voltage at which you reach ~100 mV signals. Ask for help if the signal is much wider from 50 ns or if it “rings” to the right of the peak.
7. Label the paddle with a sticker giving the appropriate voltage, dial setting, and you initials and date. You might also assign a reference name to the paddle for future measurements (e.g. #1, #2, etc.). Follow the procedure for all other paddles.
~ 100 mV