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university:courses:fieldsandwaves:m1k-emi-lab [05 Mar 2021 15:20]
Doug Mercer [Directions:]
university:courses:fieldsandwaves:m1k-emi-lab [05 Mar 2021 15:26]
Doug Mercer [Procedure:]
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 The AWG channels should be configured in Hi-Z and Split I/O mode. Turn on the channel A and B scope traces. The signals seen will likely be rather small so the vertical range settings should be 10 mV/div or lower. You may wish to adjust the vertcal possition as needed to center the traces on the screen grid. The horizontial time/Div should be adjusted as needed to view the various waveforms you pick up with the coils. The AWG channels should be configured in Hi-Z and Split I/O mode. Turn on the channel A and B scope traces. The signals seen will likely be rather small so the vertical range settings should be 10 mV/div or lower. You may wish to adjust the vertcal possition as needed to center the traces on the screen grid. The horizontial time/Div should be adjusted as needed to view the various waveforms you pick up with the coils.
  
-=====Procedure:​=====+====Procedure:​====
  
 The various electrical devices in the room (and elsewhere in the building) produce electromagnetic signals. Identify at least two different signals with whichever antenna works best. Hints: look for frequencies under 100 Hz and above 20 kHz. Some noise signals observed will be sinusoidal and some will be a series of pulses. The various electrical devices in the room (and elsewhere in the building) produce electromagnetic signals. Identify at least two different signals with whichever antenna works best. Hints: look for frequencies under 100 Hz and above 20 kHz. Some noise signals observed will be sinusoidal and some will be a series of pulses.
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 You can also try using the other higher inductance 1 mH and 10mH coils. Do they pick-up the high frequency EMI signals as well? Why or why not? You can also try using the other higher inductance 1 mH and 10mH coils. Do they pick-up the high frequency EMI signals as well? Why or why not?
  
 +=====Electric Field Directions:​=====
  
 +Up until now we have been using magnetic coils to detect varying magnetic fields. Now we will be using just an open (un-shielded) wire and the very high input resistance of the scope input to detect a changing or varying electric field through capacitive coupling. ​
  
 +{{ :​university:​courses:​fieldsandwaves:​alm-fandw-emi-fig6.png?​600 |}}
 +
 +<WRAP centeralign>​Figure 6, Connect electric field pick-up wire to Scope input.</​WRAP>​
 +
 +====Hardware Settings:​====
 +
 +The AWG channels should be configured in Hi-Z and Split I/O mode. Turn on the channel A scope trace. The signals seen will likely be small so the vertical range settings should be around 50 mV/div. You may wish to adjust the vertical position as needed to center the trace on the screen grid. The 1 Meg resistor connected to the +5 supply rail should center the signal near 2.5 V because of the internal 1 Meg resistor connected to ground on the AIN pin. The horizontal time/Div should be adjusted as needed to view the various waveforms you pick up with the wire, 5 mS/Div is a good place to start to observe 60 Hz AC power line interference.
 +
 +====Procedure:​====
 +
 +To detect the electric field surrounding 60 Hz power lines, hold the long header jumper wire near a power extension cord. **Be sure to not touch any of the header wires to any bare conductors associated with AC Mains power!**. To pick-up the biggest amplitude signal hold the header wire parallel and close to the extension cord. The longer the wires are parallel to each other the more the AC electric field will be coupled.
 +
 +Shown in figure 7 is the waveform detected when the header wire is held parallel to an AC power extension cord. The frequency is 60 Hz as expected. The amplitude is about 300 mV p-p. We know that the voltage amplitude peak to peak of the 120 V AC power line is:
 +
 +<​m>​2*sqrt{2}*V_RMS</​m>​
 +
 +Or 336 Vp-p, so the coupling factor is about 1/1000.
 +
 +{{ :​university:​courses:​fieldsandwaves:​alm-fandw-emi-fig7.png?​600 |}}
 +
 +<WRAP centeralign>​Figure 7, Electric field around AC power cord.</​WRAP>​
 =====Questions:​===== =====Questions:​=====
  
university/courses/fieldsandwaves/m1k-emi-lab.txt · Last modified: 05 Mar 2021 15:26 by Doug Mercer