Variable resistor in multisim

W1 Lab: Introduction to Process Control Lab

Instrumentation Measurement & Lab

Introduction to Process Control Lab

1. You are taking a measurement of a signal from a sensor with high frequency noise. In order to not amplify that noise through your instrumentation system, you decide to use a RC filter with a cutoff frequency (critical frequency, fc) of 1kHz after the sensor and before the amplification.

a. What kind of RC filter do you need? Design the RC filter. Be sure to use standard resistor and capacitor values and specify the tolerance. Show all work.

b. Construct the circuit using Multisim. Use the tolerances which you specified in your design.

Use the multifunction generator for the input and use both channels of the Tektronix virtual scope to display the input and output voltages.

Create a table of your input and output voltage at dc, 250 Hz, 500Hz, 750Hz, 1kHz, 5kHz, 10kHz, 50kHz, 100kHz. Measure additional frequency points in order to get a nice set of data for the drop off. Be sure to capture several screenshots of the Tektronix virtual scope.

Given the output voltage at dc, what is the voltage 3dB down? In other words, what is the output voltage at the 3dB point? You should calculate this.

Using your simulation, change the frequency of the input voltage until the output voltage is that associated with your 3dB point. What is the frequency of the signal? That is your critical frequency. Take a screenshot of the scope. Add these measurements to your table. Also, put in your report this frequency. What is this frequency called?

Create a plot of your data (you can do this easily in Excel) and copy and paste the plot into your report.

Questions:

1. Does your circuit attenuate the signal at high frequencies? What is the attenuation at 10kHz?

2. How does your measured -3dB frequency (fc) compare to your design critical frequency? Give some reasons why it is different.

W2 Lab: Digital Signal Conditioning Lab

Instrumentation Measurement & Lab

Lab 2 hints For the 2 resistors on the left, they are in a voltage divider configuration. The directions say that you need 1.25V (out of that 5V dc). This 1.25V will be across the bottom resistor which by the way is typical in a voltage divider situation. This resistor value is what you will have to calculate (this is a design issue). I would recommend using in the kohms values. The far right resistor is just a pull-up resistor, typically kohms values as well. Adjust your design for it if you need to. The oscilloscope will show the effect of the variable input, the output being a square wave varying from 0V (when the input is above 1.25V) to 5V (when the input is below 1.25V). Other voltage readings using multimeters need to be taken as well of course. ps. Oscope – right-clicking on the triangles with the numbers at the top then selecting “Select a trace” will allow you to select which channel you wish to use (change which waveform you wish to follow)

Digital Signal Conditioning Lab