New answers tagged emc
1
Referencing to N is only required for Common-Mode filtering. The Cx capacitors are not providing any Common-Mode filtering, they are creating a 2 stage Differential-Mode filter.
Cy are providing the single stage Common-Mode filtering by providing a "low impedance" circulatory path back to the LOAD, for any CM noise that may have circulate outside ...
1
Let's talk about this one first:
If you re-arrange the drawing you can see the purpose:
simulate this circuit – Schematic created using CircuitLab
CX capacitors' purpose is to provide filtering for "differential mode noise". Normally, the NEUTRAL is a current carrying conductor. So a filter for differential mode noise can be placed across ...
3
I've had trouble where the soldermask opening on the corner of the pad would be a little bit too wide so when soldering components it would short to the trace. This isn't detected by board electrical testing since the short happens when soldering.
If you trust the manufacturer to be able to manufacture according to their tolerances, and if the tolerances ...
0
A resistor on all SPI lines will make edges less steep and that's good for EMC tests.
Start from 1 kOhm.
Use CAT16 or CAT16 that have 4 independent resistors in a single package.
Slow down SPI clock if you can.
You can change layer because at 12 Mbit/s you don't really have signal integrity issues.
The bottom layer of your PCB should be GND.
The top layer ...
1
If you don't know if you need resistors or not, draw them in so you don't need to do another board.
Resistor physical size is up to you, and the resistance value can't be known beforehand. it depends on the wiring length, wiring capacitance, load capacitace, even trace width as it contributes to the trace impedance.
It also depends on what devices you have ...
2
I know the impedance might not be respected for the ethernet and CAN busses but would that really be a significant problem on such small lengths (just to go through the connector basically) ?
For small lengths impedance mismatch shouldn't be a problem. The receiver should be able to recover data with ringing and reflections.
What about the 230V/50Hz, ...
2
ESD spark events are wide bandwidth events and inject energy in the air at high frequency.
That energy can be picked up by a long PCB trace or by an external cable.
If one or more VDD traces are not stable with respect to the GND plane during ESD events, than sequential circuits like flip-flop can flip their state.
You might want to filter and decouple all ...
2
The case for the driven leg can be seen in Winter, Bruce B., and John G. Webster. "Driven-right-leg circuit design." IEEE Transactions on Biomedical Engineering 1 (1983): 62-66..
It becomes pretty apparent when you actually draw in the resistances between the electrode and the signal you're trying to amplify, which are largely at the skin interface....
2
The classic instrumentation amplifier circuit consisting of opamps 1 and 2 in your diagram have a common mode rejection ratio of 0db, otherwise called "no rejection at all". In other words, the outputs are still differential, both containing common mode noise, and still requiring a third differential stage to remove that noise. This can be seen ...
1
You have not provided any details on the target requirements and very few on the actual design of "the machine". From what I see so far, it looks more like you are afraid of shadows than trying to solve any real problem.
Let's start with basic. The FCC part 15 in US and IEC 61000 / CISPR 32 standards in Europe are most common documents that govern ...
0
If you use a shielded cable to pass through the wall of a conductive enclosure, and EMI is an issue, then you must connect the cable shield to the enclosure wall.
Ideally you would do this while maintaining the full 360 degrees conductive shield around the cable. Typically this is done with a shielded connector, this is why shielded connectors are made.
If ...
4
The purpose of plane stitch vias along the edge is to counteract the 'slot antenna' formed by planes next to each other. The edge stitch vias seal off this unintentional antenna and blocks EMI that would otherwise escape from the board edge. The vias form a 'picket fence' that looks like a dead short to RF, reflecting it back to the source.
Via spacing for ...
1
The high speed USB does require a bit of care which means:
length matching D+/- traces!
filter common mode noise from D+/- traces e.g. with a small CMC and bonding the USB shield to chassis ground
stick to the required impedance
keep sufficient distance with any other signals (3H minimum)
Via fencing won't hurt, but it must not be to close. otherwise you ...
3
Measure it? The standard will list a defined test-method and limits.
The CE mark means: "I promise that my product complies with all the relevant laws and requirements" There are lots of standards, and you need to make an assessment for each one. It sounds awful, and it kinda is, but take deep breath and read the "EU blue guide"
Falsely ...
1
The effect of grounding really depends on the frequency range you are trying to suppress.
At low frequencies (wavelength >> size of the shield) the shield can reduce the E field strength via capacitive coupling. Indeed, if the shield is not electrically connected to the rest of the circuit, it will not work: the E field inside the shield will attract ...
1
The question in the title is quite different from the one in your "Question" section. The former question is an engineering one, the latter is a pure physics concept which I'll address here. Regarding that, note that there's just one EM field/EM radiation. The "electric" and "magnetic" concepts are just two different views of ...
5
There needs to be continuous contact between the screen, the frame, and the enclosure this thing is mounted on, along the entire circumference of the opening. Outside of this conductive circumferential path, surface coatings are of no consequence.
As shown, it looks like the frame-to-enclosure contact is in four corners through the screws. The screws are ...
3
Bottom line is this. The anodizing or paint doesn't affect the shielding effectiveness of the screen, provided there is a good, low impedance (less than a couple of milliohms) bond between the screen and the chassis/box it's being mounted to.
Oh, and that there are no gaps around the edge of the screen and the chassis.
This assumes you need shielding ...
4
Henry Ott and the Grounds for Grounding folks would say it should be electrically connected to prevent EMI leakage from around the seams.
Also, the hole can be considered a slot, which can make the chassis a magnetic antenna (aka slot antenna). Making the grill electrically connected to the chassis prevents the slot antenna formation. A floating wire mesh ...
4
The anodized finish should not matter provided that the metal is grounded. This can be something of a problem through anodizing but I assume the screw to the case cuts through the oxide layer.
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The purpose is common mode suppression.
Without the caps, the isolated output will be floating and have very high impedance to the input side, but that is a problem because any stray capacitance in the transformer would couple the high frequency square wave switching waveform to the output, but the caps cause the output to have lower impedance and the small ...
0
Instead of a common VCC wire, consider a separate VCC for each LED. In this case the return current in each VCC wire will exactly match the current in its associated PWM wire, but in the opposite direction of course. Now the EMI can be greatly reduced by using twisted pairs of wire. Cat5 or Cat6 communication cable is inexpensive.
The truth is, simply ...
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