In this lab you will filter the signal from a pressure sensor that is used to monitor the height of liquid in a tube while the tube has an inflow and outflow.  The inflow from a pump generates turbulence that causes the output from the pressure sensor to be noisy - and there may be other effects.

        There are about ten experimental liquid level setups, and each setup is different.  Keep track of which unit you work with.  Here's what you need to do once you have chosen a unit.

• Locate the power supply.  It is actually three power supplies, and each power supply is separately controllable.
• Do not connect the wires from the power supply to the liquid level unit.
• Set the +25 supply - which can give any voltage from 0 to 25 volts - to 12 volts.  This will be the voltage you need to supply to the sensor to get it to work.
• Set the +6 supply to 2.5 volts.  You are going to connect this to the motor which drives the pump.
• Connect the sensor output to the oscillscope.
• Now, test whether you have everything connected together.
• Make the connections to the liquid level unit.
• Apply 12v to the sensor.  Apply the voltage at the terminals on the circuit board as indicated.  There may be two sensors - a pressure sensor and a flow sensor.  If you don't apply a voltage you will not get an output from either sensor.
• Apply the 2.5 volts to the pump.
• Measure the output from the pressure sensor on an oscilloscope.
• The oscilloscope will permit you to see a time history of the pressure sensor voltage output that includes the signal and noise.
• Set the oscilloscope to these settings on Channel 1.
• Horizontal - 5sec/div.
• Vertical - 2v/div.
• Hit the STOP button, then hit the START button to start a fresh trace.  You will not be able to see the trace until it gets to the center of the screen at which point the scope will paint the entire trace to that point as it finishes the trace.  When the trace is completely across the screen, hit the STOP button.  You now have a trace that you can get into Intuilink, and later save in a file.
• Practice bringing the data into Intuilink and saving it to a file.
• And, you should observe that there is some noise mixed in with the signal.
• Nextdd a resistor-capacitor (RC) filter at the sensor output.  Begin by using a 1.0sec time constant.  (R = 100KW, C = 10mf)
• Observe the filter output on the oscilloscope.
• Observe the input to the filter simultaneously on the second channel of the osciloscope.  (You need to put the signal lead from the sensor output to the second channel.  Note that the ground connection is already made.)
• Record both the sensor signal and the filtered sensor signal for UP, DOWN, and CONSTANT HI (2.5-3v., don't push water out the top of the tube.) and CONSTANT LO.
• Do two runs of the constant heights changing the scope setting to 0.5 sec/div.
• Repeat with a different filter (R = 10=KW, C = 100mf).
• We will need to compare the results for the two filters.
• The oscilloscope actually presents a 1.0MW load to the filter and changes the output signal.  That's something to discuss in class.
• For your report, answer the following questions.
• What were the time constant of your filters?
• For the original filter, TC =  ___________
• For the second filter, TC =  ___________
• Is the magnitude of the noise reduced at the filter output?
• Which filter does best reducing noise?  __________
• What other effects did you notice?
• Can we measure how much the noise is reduced?  That's a topic for class.