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university:courses:fieldsandwaves:m1k-emi-lab [02 Mar 2021 19:06]
Doug Mercer [Questions:]
university:courses:fieldsandwaves:m1k-emi-lab [05 Mar 2021 15:26]
Doug Mercer [Procedure:]
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 1 100 uH Inductor (101) 1 100 uH Inductor (101)
  
-=====Directions:​===== +=====Magnetic Field Directions:​===== 
- +In this part of the activity we will be using magnetic coils to detect varying magnetic fields though inductive coupling. ​Connect 10 mH and 1 mH coils to the two scope input channels on the ADALM1000 as shown in figure 1.
-Connect 10 mH and 1 mH coils to the two scope input channels on the ADALM1000 as shown in figure 1.+
  
 {{ :​university:​courses:​fieldsandwaves:​alm-fandw-emi-fig1.png?​600 |}} {{ :​university:​courses:​fieldsandwaves:​alm-fandw-emi-fig1.png?​600 |}}
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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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 <WRAP centeralign>​Figure 3, 10 mH and 1 mH coils on lap-top keyboard</​WRAP>​ <WRAP centeralign>​Figure 3, 10 mH and 1 mH coils on lap-top keyboard</​WRAP>​
  
 +One potential source of EMI radiation is the M1k PC board itself. The various integrated circuits and passive components on the underside of the board will produce high frequency electric and magnetic fields. Use the 100 uH coil from the parts kit as the pick-up “antenna”.
 +
 +Flip the M1k board over so the component side is facing up as shown in figure 4. Hold the pick-up coil vertically directly over various places on the PC board and observe the amplitude of the signals you pick up. As shown in the figure a couple of the good places to see large EMI signals is near the switching power supply regulator sections especially the inductors. Another place you might pick-up a strong signal is over the main crystal oscillator for the micro-controller. ​
 +
 +{{ :​university:​courses:​fieldsandwaves:​alm-fandw-emi-fig4.png?​600 |}}
 +
 +<WRAP centeralign>​Figure 4, Under side of M1k board facing up.</​WRAP>​
 +
 +For example figure 5 shows the more than 100 mV p-p signal seen when holding the 100 uH coil directly over the master crystal oscillator Y1.
 +
 +{{ :​university:​courses:​fieldsandwaves:​alm-fandw-emi-fig5.png?​600 |}}
 +
 +<WRAP centeralign>​Figure 5, 100 uH coil held over Y1 Crystal Oscillator.</​WRAP>​
 +
 +Why don’t you pick-up any strong signals in the analog input and output section of the board?
 +
 +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-fig6.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