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how can i filter ac noise?

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hakan

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hi,

i want to use a simple hardware which was produced by me as a simple plc. But i have problem with noise.

i need help to filter the noise.

thks.
 

Spasomat

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Hi Hakan,

it depends on your circuit. If you could be more specific it would be easier to help you.
If the signals you are interested in are much higher than the 50Hz you could perhaps get easy rid of the hum with a simple passive 1st order highpass filter.

Spasomat
 

servopump

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hi hakan,

if you try to filter ac noise on plc digital input, try 0.1 uF cap on digital input pin.

Also, you can use software to debounce the signal input.

Opto isolation will help with ground loop noise

can you give more detailes of your circuit?

servopump
 

GrandAlf

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One thing that is often ovelooked is grounding. Make sure that you have good low impedance earths and that they all share a common ground point. Then is the time to start looking at filters etc. Hope this points you in the right direction, it has certainly cured a lot of problems for me, over the years.
 

hakan

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my major problem is the noise of power suply. some times it gets noise form another component like a selenoid near it. At that time my microcontroler resets itself. i need to avoid noise from other components like power switchs.
can u advice me a passive filtering method?
 

maranaza

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If you have a resistor at the master reset pin, try to lower it. Also, check if ceramic cap is close enough to the micro supply pins.

maranaza
 

VSWR

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PLC reset

Seems you have insufficient power supply line filtering of the supply rails, feeding your PLC. What does the power supply of the PLC look like? Does it consist of three terminal voltage regulators (like LM7805), including sufficient electrolytic capacitors? Please describe these circuits in detail and we may help you. A circuit diagram in JPEG or GIF format will be of great help. Use the 'Add an attachment' button at the lower part of the 'Post a reply' screen.

Another noise pick-up might be any input data lines connected to the PLC. What does they look like? What's connected to the PLC? Are these lines screened, having the screen connected to ground at each end? Any capacitor at the RESET input line?

hakan said:
my major problem is the noise of power suply. some times it gets noise form another component like a selenoid near it. At that time my microcontroler resets itself. i need to avoid noise from other components like power switchs.
can u advice me a passive filtering method?
 

jzaghal

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Hi,

Seems that you do not have enough shielding and grounding ??

Bye.
 

barrybear

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Fast switching will always produce noise but this is not ac noise it is normally heard as a splash.It can be removed with a snuber ciruit (capacitor in series with a resistor.

If you can not see any ac hum noise using an osiloscope on your power lines( while the supply is under load ) then your problem must origanat from your comonents and set up. Try various methods of grounding or icolating see if the problem gets worse .I once cured a bad hum by using an isolating transformer on a mixing desk.
It would be a good idea if you could provide more information and diagram.
Barrybear
 

hakan

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i use 7805 with standart capacitors. i think there is some noise because of inductance of other devices.
 

Analyzer

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Hmm Maybe this will be useful for you : Use big electrolytic capacitors between 7805 out pin and gnd(For example 1000 mf is enough) and connect a big ferride inductor serially to 7805 out.Like this:

7805 out -> +1000mf
Gnd -> -1000mf
7805 out -> Ferride inductor
Ferride inductor -> To circuit

You can easily find inductors or you can build it.Last of all check pm.
 

padspcb

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you must not forget to place a small 104 capacitor near the 7805
in both pins, otherwise it will oscilate...
also electrolitics have big L so 7805 gets lost in entry ripple
try setting reset very heavy, and put diode to vcc
best
 

cheolim

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Hello, hakan

I cannot be sure but I think you have two kinds of problems.
One is surge or switching spike from power supply and the other is
counter electromotive force from inductance like solenoid.
In first case, you can solve it with varistor or zener diode coupled with
resistors in front of the 7805 regulators.
Other second case, please don't forget to place the rectifier diode on both
terminal of solenoid inductor drive.
I hope above can help you.

Good luck.
:roll:
 

pnielsen

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Regarding AC noise "Hardware". It depends on many factors. The best starting point would be to look at notch filters. The frequecy and Q is determined in the hardware equations that you are using
 

2000

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noise problem

hello pal,

I'm having exactly the same problem, in my project I drive 4 relays using an uln2003 darlington driver and this relays drive 127V to the controls of a motor. The noise makes the uc to reset and generates undesirable interruptions like buttons ints. Is it due to the noise in the power line? I'm using this dam 7805 and a 100uF eletrolitic cap in its input/output.... my reset ckt is a simple 10uF cap and 8k2 resistor... what could be done to make it "noise proof"???

regards,

2000
 

pnielsen

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Re: noise problem

2000 said:
hello pal,

I'm having exactly the same problem, in my project I drive 4 relays using an uln2003 darlington driver and this relays drive 127V to the controls of a motor. The noise makes the uc to reset and generates undesirable interruptions like buttons ints. Is it due to the noise in the power line? I'm using this dam 7805 and a 100uF eletrolitic cap in its input/output.... my reset ckt is a simple 10uF cap and 8k2 resistor... what could be done to make it "noise proof"???

regards,

2000

There are many good suggestions that have been submitted. The 127 motor coil can cause allot of problems. If you take a .1uF/600wvdc and a 100 ohm resitor in series with the cap. Then place this "snubber" accross the load it may help. For you application I have used Opto isolators. These 6 pin devices isolate the drive circuit and the dirty outside world noise
[/i]
 

gpoletto2

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Don't forget to add a large amount of 104 spread arround your circuit. One on every IC is a good idea and as near as posible to the supply lines, and also a big electrolitic, say about 10 uF or so, every four or five ICs in you project. Another good point is to have a big, low impedance ground plane where all the chips GND are routed to.

Good luck
 

icatar

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Dear Hakan.
Some microcontrollers are more resizt of electrical noise,spike and flick. .Which is yours?
If controller have Built in Power on reset , brown out detect and WDT features like (microchip 16c74,16f877 , not 16f84) you will have less problem.
And you have to use 100nF cap very near Vcc-Gnd pin of controller.and dont select 7805 regulator caps more than 1000microF.use
a separeted coil of transformer for controller supply voltage(+5v) beside of other compenent supply voltage like relay etc.
servopump advice is good.
"if you try to filter ac noise on plc digital input, try 0.1 uF cap on digital input pin"
and be sure ,the digital input voltage must be less then +5v .
 

The Svin

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I had problems with noise in some ware connected to LPT from signal catcher, solved it by simple thing - connected the ware in parallel with other ware with resistor and grounded the resisor on system block ground screw, so Amps were devied and only strong signal was cought as logical 1 by LPT. Keeping in mind this section of forum name I assume that the question was about PC? Wasn't it?
 

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