Introduction to the Oscilloscope
BIONB/BME/ECE 4910, Spring 2015
In this short lab protocol, you will learn to use the Tektronix TDS1002
oscilloscope to visualize electrical events by sending it stimulation pulses from the Lab
Chart software. Although you will visualize, acquire and analyze almost all of your
biological voltage events on the LabChart software, the oscilloscope will still be a handy
tool to help solve technical problems quickly. The file labeled "OscilGuide2015" will be
a necessary reference for this exercise.
1. General oscilloscope operation
Examine the operation of the oscilloscope using signals from the Power Lab
connected to the oscilloscope.
Turn on the oscilloscope and adjust it as follows:
Oscilloscope:
CH1: Volts/div = 1 V
CH1: coupling = DC
CH2: Volts/div = 1 V
CH2: coupling = DC
Time/div = (M) 5 msec
Trigger Mode = AUTO
Start a new Lab Chart file. Under “Setup- stimulator”, leave everything the same
except set the stimulus controls to “Manually”, and the parameter values to Repeats:
infinite, Max Repeat Rate: 2 Hz, Pulse Height: 2 V and Pulse Width: 0.005s. This will
send a series of 2 V square wave pulses to channels 1 and 2 of the oscilloscope (Pulse
duration 5 ms; Delay, 0; output from the “+” BNC port of the PowerLab box split to the
oscilloscope channels). Start LabChart and press “Stimulate”. You will see two pulses
running across the oscilloscope screen. Turn the position knob for channel 2 to move the
waves apart. The oscilloscope display is essentially a graph of voltage against time. Time
is indicated by the horizontal distance, left to right, and the vertical displacement is a
function of voltage input. Change the time/div control to 2.5 msec. Notice that fewer
and wider pulses now travel across the face of the screen, at a rate of 2.5 msec/div. We
can measure the elapsed time between any two points on the same horizontal line by
measuring the distance between them and multiplying it by the horizontal sweep speed of
the trace. The continuous grid lines on the screen are one division apart, so if the
distance between two points, A and B, is 6 div and the sweep is 2.5 msec/ div, then the
elapsed time between A and B is 6 div x 2.5 msec/div = 15 msec (0.015 sec).
The two pulses should be the same size because the voltage input and sensitivity
are the same for both. Now increase the oscilloscope sensitivity of CH1 by a factor of
two, from 1 v/div to 0.5 V/Div. Note that the vertical displacement of the upper trace is
now twice that of the lower one, yet the voltage input to both channels is equal. The
voltage input is calculated as follows: Vertical displacement x volts/div = voltage input.
If the vertical displacement on the upper trace is 2 div and the lower trace is 1 div, then:
Upper: 2 div x 0.5 v/div = 1 V
Lower: 1 div x 1 v/div = 1 V
Notice that the pulses do not always begin to move across the screen at the same
position on the oscilloscope screen. Use the oscilloscope’s trigger function to initiate the
trace in the middle of the screen (M pos 0.00) at the rising phase of the pulse. To do this:
Under the trigger menu, set the Trigger Source to CH1 (CH2 would work too), set the
Trigger Mode to Normal, and adjust the trigger level (right arrowhead) to the middle of
the screen. The oscilloscope trace is now triggered by the “rising” voltage deflection, and
the first pulse should now start on the left side of the screen
Now, adjust the Trigger Level on the oscilloscope until the pulse consistently
appears at the middle of the screen by turning the Horizontal position knob (watch the
arrowhead move on the top of the screen); switch the trigger slope to “falling” and note
the shift in pulse position. Remove CH2 from the display by pushing the CH 2 menu
button. Spend a little time playing with voltage and time adjustments until you feel
comfortable with their functions.
2. Single and trains of stimulus pulses recorded on the oscilloscope: To examine a
single stimulus pulse on the oscilloscope, make the following adjustments to the
oscilloscope.
Oscilloscope:
CH1: Volts/div = 5 V
CH1: coupling = DC
Time/div = 10 ms or 1 s
Trigger Mode = AUTO
First set up the software to send out a 5 V, 5 ms pulse (Repeats: 1;
MaxRepeatRate: 0.1Hz) to the oscilloscope CH1 (Time/div: 10 ms). Keep manually
repeating the single pulse output and you should see it appear on the oscilloscope. Again,
note that the pulse occurs at different places on the oscilloscope screen. Trigger it to start
at the beginning (left side) of the screen. To produce a stimulus pulse train that is
triggered to start on the left side of the screen, send out a repetitive pulse of 5 ms
duration, for 10 sec (Repeats: 400; MaxRepeatRate: 40 Hz; oscilloscope time/div: 1 s).
Note that it takes some time for the signal to appear on the oscilloscope. What is that?
Now you are ready to determine the time constant of the provided RC circuit using the
stimulation and acquisition/analysis features of the LabChart software.