EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: amar on March 23, 2013, 07:51:08 am
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hi .. i am going to design a micro controller based circuit for industrial application.
any suggestion to make circuit for noise immunity
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Make up opto-coupler I/Face boards for both Inputs and Outputs. Usual current limit/zener clamp/capacitor filters.
Run the Interconnect to the MPU board via a mult-core shielded cable. Shielded ONLY at the MPU P/Supply, all at
one point.. For Linear Inputs, use IL300s or similar for the Isolation. I've posted a circuit a few weeks ago.
If you need "remote" power, I'd suggest an Isolated DC-DC converter. There's HEAPS out there. Lots of caps :-)
Any other questions?
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Proper decoupling of the supply current and shielded enclosure. And as digsys said. ;)
You need to post more information if you want more details, schematic or detailed description.
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hi .. i am going to design a micro controller based circuit for industrial application.
any suggestion to make circuit for noise immunity
EMI and EMC are almost larger than life subjects, even ignoring any formalities of compliance.
Also, there are myriads of "industrial applications" so you need to be more specific if you want concrete advice. The tips you got already are good but there is more, depending on the specifics.
Interesting info would revolve around frequencies, voltage levels, circuit impedances, distances between components of the solution as well as distances and modes of interaction between aggressor and victim equipment.
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Thanks for reply
i am using opto isolation for I/O , .1 micro farad caps on VCC & GND of every IC and using different power supply +24 V for I/O &+5 V for MCU and driver circuit for different ground.
inputs are push buttons or proximity sensors and output is inductive load which is drives by relays.
is it sufficient or something more is required.
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The most important factor is the PCB. Get at least one (mostly) solid layer of copper connected to ground. Never ever use split ground planes. It doesn't mean you need more than two layers though. If you optimise the connections in the schematic you can route most traces on the top layer and use the bottom layer as a mostly solid ground plane.
If you use TQFP packages with multiple power pins, create a copper pour for the power underneath the TQFP package which connects all the power pins.
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Never ever use split ground planes.
i dare say SPLIT EM ! Notably in a power return plane , a shield ring and a logic ground plane. he's driving inductive loads. the return currents should go in to the load return ground NOT into the logic or analog ground !
shield ring should be tied to main ground using ferrite bead . shield ring to be hard connected to chassis.
power return ( power ground) to be connected at 1 point only to logic ground. that node should be currentless.
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The most important factor is the PCB. Get at least one (mostly) solid layer of copper connected to ground. Never ever use split ground planes. It doesn't mean you need more than two layers though. If you optimise the connections in the schematic you can route most traces on the top layer and use the bottom layer as a mostly solid ground plane.
If you use TQFP packages with multiple power pins, create a copper pour for the power underneath the TQFP package which connects all the power pins.
Could,t agree more.
Also keep all your connections to the outside on one side of the board.
Try to decouple all cables entering the board with 10 nF if possible.
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Never ever use split ground planes.
i dare say SPLIT EM ! Notably in a power return plane , a shield ring and a logic ground plane. he's driving inductive loads. the return currents should go in to the load return ground NOT into the logic or analog ground !
That is an excellent recipy... to create a transmitting and/or receiving antenna for interference. IOW an EMC certification nightmare! If you have large return currents, place the power connectors close to the connectors for the loads. Problem solved.
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Never ever use split ground planes.
i dare say SPLIT EM ! Notably in a power return plane , a shield ring and a logic ground plane. he's driving inductive loads. the return currents should go in to the load return ground NOT into the logic or analog ground !
shield ring should be tied to main ground using ferrite bead . shield ring to be hard connected to chassis.
power return ( power ground) to be connected at 1 point only to logic ground. that node should be currentless.
I would split them with a star ground.
I made a product for a automotive environment. The analog section had its own ground plain and Linear regulator.
The uC had its own ground plain and linear regulator. I then had two heater elements tied into the star ground (5A). It did a really good job keeping the noise level down.
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Common mode chokes are your friend, especially with long communication busses.
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Thanks for reply
i am using opto isolation for I/O , .1 micro farad caps on VCC & GND of every IC and using different power supply +24 V for I/O &+5 V for MCU and driver circuit for different ground.
inputs are push buttons or proximity sensors and output is inductive load which is drives by relays.
is it sufficient or something more is required.
You really don't need optoisolation if your inputs are pushbuttons on the same PCB, and you also don't need it for your outputs if they are relays, to drive the relays you can use the ULN2003
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Opto-isolation can be confusing and give a false sense of security when applied wrong. The stupidest thing I've seen is an optocoupler driven by an open-collector output comparator to create an open collector output on the same ground potential. The whole optocoupler could have been omitted!
The rule of thumb is: with opto-isolation comes a seperate isolated power supply. If everything is on the same ground potential then opto-isolation is useless.
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Opto-isolation can be confusing and give a false sense of security when applied wrong. The stupidest thing I've seen is an optocoupler driven by an open-collector output comparator to create an open collector output on the same ground potential. The whole optocoupler could have been omitted!
The rule of thumb is: with opto-isolation comes a seperate isolated power supply. If everything is on the same ground potential then opto-isolation is useless.
True, Use a DC/DC Isolated converter to get your two isolated voltages. Or have the other side supply your power... (like USB -> FTDI <opto> whatever <-power)
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If everything is on the same ground potential then opto-isolation is useless.
Not always true. I've often needed to do this. Sometimes you have a very tight packed MPU section, and you need to sort out
Digital gnd, Analogue gnd and sometimes Reference gnd - plus you're restricted to I?O positions. In cases like these I OFTEN
add opto-couplers to allow me to run the 0V bus around the MPU "mess" and re-reference it to DC Supply.
This is especially handy when using mixed Voltages. For analogue, I do the same with linear-optos. It's a 2nd level of safety.
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If everything is on the same ground potential then opto-isolation is useless.
Not always true. I've often needed to do this. Sometimes you have a very tight packed MPU section, and you need to sort out
Digital gnd, Analogue gnd and sometimes Reference gnd - plus you're restricted to I?O positions. In cases like these I OFTEN
add opto-couplers to allow me to run the 0V bus around the MPU "mess" and re-reference it to DC Supply.
This is especially handy when using mixed Voltages. For analogue, I do the same with linear-optos. It's a 2nd level of safety.
I would have to see a example of this ;D
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Try to separate low voltage signal cables from power cables. If possible, don't tie them together as transients and ESD might couple through the cable insulation and cause trouble with latchup and false triggering.
Some PICs have issues with edge triggering on the I2C bus that triggers the internal state machine to go out of sync. The errata solution was to toggle the I/O a few times to get back in sync.
Not all problems can be solved with just one level of filtering. Cascading filters with different topologies and properties (fast/slow, high/low voltage etc) can help.
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Thanks to all for share your experience