Instruction manual

ManualsBrandsB&K Precision ManualsPower Tools2530B

Oscilloscope and EKG sensor

Equipment DataStudio, BK Precision model 2530B oscilloscope, function generator, 2-3 foot

coax cable with male BNC connectors, BNC to female banana adapter, 1 voltage sensor, EKG

sensor, EKG Sensor Electrode Patches

Remark The oscilloscope is a diﬃcult instrument to understand, but it is also a very impor-

tant instrument. Studying this write-up carefully before the lab will be worthwhile. This

lab cannot be approached casually. The basics of a heart rate meter is an oscilloscope and

you will be using an EKG sensor to monitor your heart rate.

1 Introduction

The standard instrument for examining time dependent voltages in a circuit is the oscillo-

scope, or “scope” for short. Even if you are doing a DC experiment it is a good idea to

look at the circuit with a scope. You might ﬁnd a large AC signal symmetric with respect

to ground that does not show up on DC instruments but is aﬀecting your experiment in

undesirable ways, such as overloading a sensitive ampliﬁer. Oscilloscopes are ubiquitous in

the medical profession. They are seen next to hospital beds showing the electrical output of

a heart. They are used extensively in operating rooms.

A voltage which depends on time can be drawn on graph paper with the voltage on the

vertical axis and the time on the horizontal axis. If the voltage is periodic (repeats itself

after one cycle) an oscilloscope will present a similar curve. By adjusting the scope it is

possible to display part of one cycle or many cycles of the waveform. Properties of a periodic

voltage, such as shape, peak-to-peak amplitude and period, can be measured. Scopes have

other uses, but these are the primary subjects of this lab.

The oscilloscope is a sophisticated instrument. Competent use depends on understanding

how this instrument works. It is often necessary to consult the instruction manual for a

particular scope in order to use it eﬀectively. The basic ideas are usually the same but are

implemented in diﬀerent ways.

In this lab you will become familiar with 2 oscilloscopes, the model 2530B made by

BK Precision, and the DataStudio scope. Both these instruments do very much the same

thing except that the controls on the BK are mostly knobs and switches and those on the

DataStudio are icons and buttons. The DataStudio scope is digital. The input waveform is

digitized and stored, at least for a while.

In the last section of the lab you will be using an EKG sensor. An EKG sensor monitors

your heart rate by measuring the distribution of dipoles in the heart. The EKG sensor will

be used in conjunction with the oscilloscope to see your heart cycle as a function time. You

will determine the time of your P, Q, R, S, T cardiac cycle. Each letter represents the wave

function of your heart. The P wave is the initial pulse and that goes through the atrial

muscle. The Q, R, S is the electrical waveform in the ventricular muscle The Q wave is

down, R is up and the S is down. The last part is the T wave form. It represents the

repolarization of the ventricles.

Summary of content (13 pages)

PAGE 1
Oscilloscope and EKG sensor Equipment DataStudio, BK Precision model 2530B oscilloscope, function generator, 2-3 foot coax cable with male BNC connectors, BNC to female banana adapter, 1 voltage sensor, EKG sensor, EKG Sensor Electrode Patches Remark The oscilloscope is a difficult instrument to understand, but it is also a very important instrument. Studying this write-up carefully before the lab will be worthwhile. This lab cannot be approached casually.
PAGE 2
Description of How a Scope Displays a Single Periodic Voltage A periodic function in time is one that repeats itself again and again, such as a sine wave or a square wave. A scope can display a voltage that is periodic in time in exactly the same way. The periodic voltage is connected to the vertical input of the scope, and if the scope is adjusted correctly, a graph of the voltage as a function of time appears as a stationary trace on the screen of the scope.
PAGE 3
the electron beam is turned on and the time base oscillator applies the voltage ramp to the horizontal axis. The input voltage is applied to the vertical axis. The signal is swept across the screen from left to right at a constant speed. This takes a time P. At the same time the vertical deflection of the signal is proportional to the input voltage. A spot of light is observed to move across the screen if the sweep speed is slow enough. This spot of light traces the input voltage for a time P.
PAGE 4
slope of the input voltage. If VT is kept the same but triggering were set to occur on the negative slope of the input signal, at what points of the input signal in Fig. 3 might triggering occur? How about a negative VT and positive slope? A negative VT and a negative slope? • Fig. 3 shows plots of three ramp or sweep voltages. A given ramp voltage, no matter which of the three plots it is associated with, corresponds to the same horizontal position of the beam on the screen.
PAGE 5
box. After the name of the box, in parentheses, are the numbers of the controls that appear in that box. As you read, identify the boxes in Fig. 4. The box names are hard to read; the numbers are not. “FUNCTION” BOXES OF BK SCOPE (Numbers in parentheses refer to the controls in the box) • POWER Button (2) turns the scope on and off. • VERTICAL(3-4)- This box is really divided into two boxes. The scope has two possible input voltages.
PAGE 6
13. CH2 VOLTS/DIV control. Adjusts the vertical sensitivity for channel 2 in fixed amounts. 14. CH2 INPUT JACK. Not needed in this lab. 15. Horizontal TIME/DIV control. Adjusts the rate, in discreet steps, at which the electron beam is swept across the screen. 16. HORIZONTAL POSITION control. Adjusts the horizontal position of the trace. 17. AUTO button. 19. External Trigger. The connector at which an external trigger signal is fed into the scope. Not used in this lab.
PAGE 7
4.1 Preliminaries Remove any input cables to the scope. Turn on the scope (2). In a few seconds you should see a trace which is a horizontal line. If you do not, check your initial control settings and press the AUTO button. Leave the trace centered. Turn the time base switch (15) to 0.25 s and note the light spot move slowly across the screen until it gets to the right hand side of the screen. What happens then? Investigate the effect of turning the time base knob (15).
PAGE 8
Connect the 50 Ω output of this oscillator to the CH1 vertical input (9) of the BK scope using the coaxial cable. See Fig. 5. Figure 5: Set the AMPL knob full CCW and turn on both the oscillator and scope. Adjust the function generator for about a 1 kHz sine wave and turn the AMPL knob to the center. On the Oscilloscope adjust the Time/DIV and Voltage/DIV knob until you see a reasonable sinewave signal. Vary all of the controls listed below leaving the parameters of the input voltage constant.
PAGE 9
4.3 Other Waveforms and Functions • Observe square and triangular waveforms from the function generator by pushing the appropriate buttons. The frequency is not critical, but around 1 kHz works well. 4.4 Measuring Waveform Parameters In this section you will be looking at AC waveforms again. A useful function of a scope is to measure the peak to peak voltage and period of a voltage waveform. Display a 1 kHz triangular wave on the scope.
PAGE 10
DataStudio scopes is that in the DataStudio scope the controls are icon buttons, and a slider is used for the trigger level and slope. It is a small triangle in a vertical strip at the very left of the scope screen. The default trigger voltage is 0 with positive slope. There are only 2 trigger options in the DataStudio scope. The default is triggering the signal on the rising level. The other option is the falling level.
PAGE 11
You will repeat the steps of the bullet points in section 4.4 of measuring the waveforms. The difference is that all three waveforms of the function generator will be at 2 Khz. The DataStudio scope will be used to determine the peak and the peak-to-peak voltages of all three wave forms. You may have trouble getting a trace on the DataStudio scope. This may be due to the fact that the default trigger level is 0. Try adjusting the trigger level for a slightly positive voltage.
PAGE 12
Figure 6: At this point you should be using the smart cursor to make all your measurements for the following activities. 1. Measure the EKG of a person who is at rest. Person whose EKG is being measured should relax, remain still, and breathe normally. Someone else should operate the computer while data is collected. 2. Next measure the EKG of the same person while she or he is standing up. 3. Measure the intervals between P-Q, QRS, and Q-T. An example of an EKG signal is shown in Fig. 7.
PAGE 13
Reattach the sensor wires to the electrodes on the person within thirty seconds after the exercise is done, and measure the EKG. Compare and contrast the EKG after mild exercise to the resting EKG. Use the smart cursor of the DataStudio oscilloscope to measure the differences. What are the differences and the significances of said differences? Now, reverse the placement of the electrodes (place the green alligator clip on the left electrode and the red alligator clip on the right one).