We had to play around with the value of R2 until we got the results we wanted. It works by taking and reading signals from the heart using leads that are attached to an electrocardiograph machine. Anything too far above this will not give you the results you are looking for because the op amps were only getting a certain amount of power of -15 and +15 V. Compare the output of the function generator to the output of your instrumentation amplifier and look for a gain of close to 1000 V. (Vout/Vin should be very close to 1000). This circuit contains three different stages wired together in series with a LabView program. Instrumentation amplifiers are used where great accuracy and stability of the circuit both short and long-term are required. The resistors in the instrumentation amplifier were calculated with a gain of 975 to ensure that the small signals from the heart can still be picked up the circuit. This circuit contains three different stages wired together in series with a LabView program. The Instrumentation Amplifier (IA) resembles the differential amplifier, with the main difference that the inputs are buffered by two Op Amps. The link below contains the schematic used for the op-amps in this instructable. An ECG is a test that measures the electrical activity of the heart by recording the heart's rhythm and activity. http://www.ti.com/lit/ds/symlink/ua741.pdf, Image Source: http://ak0.picdn.net/shutterstock/videos/17671660/thumb/1.jpg. This labview block diagram is designed to analyze the signal going through the program, detect ECG peaks, collect the time difference between the peaks, and mathematically calculate the BPM. While this circuit will amplify a small signal sensor, the poor gain accuracy in the presence of noise would not be useful for instrumentation purposes. The resistive brige could be an RTD or a strain gauge on a load cell. At point 1 in the circuit, the voltage will be considered as V1. 965–973, Dec. 2011. On the other hand, there are applications where we need precisely the opposite function, called integration in calculus. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Please note that the lowest gain possible with the above circuit is obtained with Rgain completely open (infinite resistance), and that gain value is 1. Generally, biological/bioelectric signals have low amplitude and low frequency. Likewise, the voltage at point 2 (bottom of Rgain) is held to a value equal to V2. on Step 2. In the schematic it appears they are connected to a power source, but I don't see that in the breadboard. We used the function generator to send a sine wave with an input amplitude voltage of 20 mV to our instrumentation amplifier. [2]“High Performance Electrocardiogram (ECG) Signal Conditioning | Education | Analog Devices.” [Online]. This produces a voltage drop between points 3 and 4 equal to: The regular differential amplifier on the right-hand side of the circuit then takes this voltage drop between points 3 and 4 and amplifies it by a gain of 1 (assuming again that all “R” resistors are of equal value). Glen Brisebois, in Analog Circuit Design, Volume Three, 2015. Circuit Description. Test frequencies around 60 Hz as well to make sure that no other frequencies are being filtered out accidentally. Connect all three circuits in series by connecting the output of the instrumentation amplifier to the input of the notch filter and the output of the notch filter to the input of the low pass filter. That voltage drop causes a current through Rgain, and since the feedback loops of the two input op-amps draw no current, that same amount of current through Rgain must be going through the two “R” resistors above and below it. The range for biological signals will fluctuate a little in the body so as long as you are not off more than a few Hz, your circuit should still work. 1. [3] “ECG Filters | MEDTEQ.” [Online]. Available: http://www.analog.com/en/education/education-library/articles/high-perf-electrocardiogram-signal-conditioning.html. http://www.ti.com/lit/ds/symlink/ua741.pdf, BEAM Solar Powered Pummer (Heart Shaped PCB), Digital Measuring Roller Using Microbit & Tinkercad, Pocket Dice! This is because the first stage of an instrumentation amplifier has internal output voltages that can clip at unspecified levels. Modern operational amplifiers (op amps) and instrumentation amplifiers (in-amps) provide great benefits to the designer, compared with assemblies of discrete semiconductors. A practical instrumentation amplifier circuit designed based on uA 741 op amp is shown below. We chose this cutoff because the widest diagnostic range for an ECG is 0.05 Hz - 150 Hz, assuming a motionless and low noise environment [3]. Here, the op-amp circuit would generate an output voltage proportional to the magnitude and duration that an input voltage signal has deviated from 0 volts. allows an engineer to adjust the gain of an amplifier circuit without having to change more than one resistor value Instrumentation Amplifier provides the most important function of Common-Mode Rejection (CMR). Available: http://www.medteq.info/med/ECGFilters. The outputs from these amplifiers are used for further analysis and they appear as ECG, EMG, or any bioelectric waveforms. 4. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. When wiring the circuits together, make sure that the power strips for each breadboard are connected and the ground strips are all connected to the same ground terminal. 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