Editing Laboratory Preparation (section)

== Gain Matching and Setting CFD Threshold ==

===High Voltage Setup (From The Cart)===

[[File:POWERSUPLY_VSET.png|thumb|upright=1|left|alt=a diagram of the power supply menu|A flow chart for using the CAEN N1470 menu. (You need only concern yourself with the blue boxes for now)]] 
'''1. check/set high voltage from the power supply'''

The Powersupply we use is the CAEN N1470. This is a 4 channel power supply that lets us control very high voltages (very cool). Unfortunately, you need to go through a very convoluted menu to change anything this power supply does (not very cool). It is our intention in writing this section to reduce the headache this menu causes as much as possible. 

When you have successfully located and identified the power supply, hopefully, the first thing you notice is the small rectangular screen located in the top quarter of the chassis. Notice also that there is a knob right below the screen (it glows blue when on). You will use this knob to navigate or change anything in the menu. The knob has three actions: Scroll CW, Scroll CCW, and Push. Any time you perform one of these actions, something on the screen will change.

Scroll CW until the number for the channel you want is in the top left corner. Push the knob, the top right box will turn orange. Scroll until the bottom right box says VSET. Push the Knob, the bottom right box sill also turn orange. Scroll until the digit you want to change is highlighted blue. Push the knob. Scroll CW to increment the number and CCW to decrement the number. Push the knob when you want to exit. Scroll until VSET is highlighted blue. Push the knob again, bottom right turns green. Scroll until you see EXIT. Push knob. Now everything is green and you are free to select another Channel.

===Max Signal Size===

[[File:Max_signal.png|thumb|upright=.85|right|alt=Oscilloscope screen with persistence turned all the way up. You an easily see max signal.|What a max signal should look like.]][[File:Dark_current.png|thumb|upright=.85|right|alt=Oscilloscope screen with the trigger set so that it triggers on dark current.|What the Dark Current should look like. Persistence turned up to make image more clear.]]
[[File:Threshold.png|thumb|upright=.85|right|alt=picture of oscilloscope at correct threshold|This is what a waveform with a properly set threshold will look like. Persistence turned up to make image more clear.]]

Change the persistence on the oscilloscope to infinity and and let it run for about 40 seconds. Choose ad dense patch of signals and this is now your max signal value.

===Dark Current===

Adjust the trigger on the oscilloscope so that it constantly triggers. The line should get onsidersbly darker because it is constantly resetting the screen.

===Setting Threshold===

[[File:CFD_VoltageAdjust.png|thumb|upright=0.85|right|alt=picture of where to stick the probes|Positive lead should go in Red Hole. Negative lead should go to green screw (or anywhere grounded on chassis really). Screwdriver should go in orange hole.]]

'''1. Determining Threshold'''

Adjust the trigger on the oscilloscope until it is a few mV above the Dark Current. 

You want it to be high enough that it is not constantly triggering on the dark current but still low enough that it catches all real events. 

Take note of this trigger voltage and proceed to the next step.

'''2. Setting Threshold'''

For this part, a Voltmeter and a screwdriver must be used. Insert the positive probe of the voltmeter into the hole to the left of the T (in the image the whole colored in red). Ground the other probe on the screw (colored green or any other grounded part). Lastly insert the screwdriver into the hole to the right of T (colored orange). You should get a reading off the voltmeter that changes as you turn the screwdriver. Turn the screwdriver until the voltmeter reads off the trigger current you noted before. 

Note: the voltages you read will be off by a factor of 10 so divide you readings by 10 to get the right number.

The holes labeled z are the DC offset voltage, for our purposes they can left untouched.