What is the procedure for doing differential TDR on the 11800 series?
Connect the two lines that you wish to measure to the two inputs to the SD24. Be sure to use proper anti static techniques in handling both the cabling and the inputs to the SD24.
Step 1) Initialize the oscilloscope
Select the Utility main menu. Select Initilize from the menu, then Initilize from the pop-up menu. All traces should be removed from the screen and the instrument should have the Waveform menu selected.
Step 2) Select differential TDR
After the Initialization, the instrument will be in the Waveform menu. Select Sampling Head Fnc's from the menu. From the pop-up menu select Diff TDR Preset. This will create two waveforms on screen, a positive going TDR pulse and a negative going TDR pulse.
Step 3) Creating the differential trace
At the top right hand corner of the screen, there is an icon named Def Tra. Select this icon. A full screen menu will come up that is labeled Vertical Description. From this menu, create a description that is M1-M2, then enter that description. Select, in order. M, 1, -, M, 2. Near the bottom middle of the menu there is an Enter Desc selection. Select that function.
You should now have three traces on screen. See the drawing below.
Remember the cursors are reading single ended measurements, while you have created a trace that has twice as much amplitude on the TDR step. So when you are reading the cursor values of the impedance, you need to use the x2 reading. If you have an older instrument that does not have that feature, you need to double the Ohms reading.
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