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Modified Block Diagram

Part 5: op-amp circuits

Before building a circuit to condition the signal, you will build a couple of simple op-amp circuits to get afeel for what to do.

5.1 inverting circuit

The inverter is one of the simplest op-amp circuits. This circuit simply changes the sign of a signal. Theschematic diagram of an inverter is shown in Figure 6.

  • Build the inverter using two 10 k ohm resistors and an LM741 op-amp.
  • Input the signal from the function generator to the circuit.
  • Branch the input cable with a BNC T-connector. Connect this input to Channel 0 on Module 1 of the SCXI.
  • Connect the output signal from the circuit to the Channel 1 on module 1 of the SCXI.
  • When you run the VI, you may need to adjust the scales on the X and Y axes.

You should see that the output is an inverted version of the input.

Inverter and Inverting Gain Circuits

5.2 inverting gain circuit

The inverting gain circuit changes the sign of the signal and multiplies the amplitude. Increasing the amplitudeof a signal can be very important in distinguishing subtle signal characteristics. Quantization errors result when a signalcharacteristic is too small to be detected by a measurement system. (You will learn more about quantization errors in lecture, and onpages 249-250 in your text.)

  • Replace the feedback resistor (R2 as shown in Figure 5) in your inverter circuit with a 100 k ohm resistor. This will causethe input signal to be inverted and amplified by a factor of ten.
  • Run the VI again.

With the amplification, the input offset of 800 mV has increased to an 8 V output.

Note: Using the data acquisition card to view the signal, you may saturate the ADC with the amplified signal. Allyou will be able to see is a flat line near +5 V or–5 V.

Part 6: bias correction

For the amplified signal to be read correctly, the 800 mV bias must be removed. A two step process will be used toremove the bias:

  • A Trim Potentiometer will be used to step down a 12V DC signal to 800 mV.
  • A Differential Amplifier circuit will be built to subtract this stepped down voltage from the sine wave.

The result will be an 80 mV sine wave with zero mean.

6.1 trim potentiometer adjustment

Use the 10 k ohm trim potentiometer provided to build a voltage divider as shown below.

  • Connect one end lead of the potentiometer to the +12 V bus.
  • Connect the other end lead to the–12 V bus.
  • Connect a voltmeter across the wiper lead and ground to measure the output.
  • Adjust the potentiometer resistance until the voltage on the wiper lead is 800 mV.
Voltage divider circuit

6.2 differential amplifier

You will build a differential amplification circuit to subtract 800 mV from the sensor signal. A differentialamplifier is shown in Figure 8 below.

  • Use four 10 k ohm resistors to subtract the voltage divider output from the sensor signal. It is unlikely that the resultingoutput signal will be a zero-mean sine wave as desired.
  • Adjust the screw on the potentiometer to "trim" the offset of the sine wave to zero.
  • Amplify the difference between the signals by replacing the R2 resistors so that R2>R1. Replace the R2 resistors with 100 k ohm resistors.

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
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Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
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Brian Reply
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industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
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scanning tunneling microscope
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what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
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what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
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What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Introduction to mechanical measurements. OpenStax CNX. Oct 18, 2006 Download for free at http://cnx.org/content/col10385/1.1
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