MOTOR or CONTACTOR noise (load cell connected to machine body)......

Dear friends ,

I have an application where i am connecting the load cell to a machine with ac motor.The machine shaft moves up and down through the contactors .

1. Machine is driven up or down from optocoupled outputs of the relays .The relays drive the contactors which move the machine up or down.
2.Load cell is connected to the machine mechanically bolted.
3.Load cell is powered from the pcb 5V and ground which are given to the load cell from the Uc card .
4.uC card contains other peripherals also whose ground is commonly connected to the Adc section , Load cell power supply and rest of the circuit except the relays and proximity sensors.
5. The motor is also connected to the machine(ac motor).

Now when the machine is not moving there is no peak on the load cell supply (it is almost smooth 5V dc) as seen on oscilloscope.
when the relay is turned on there is a very big visible spike around 10V on the Load cell supply .I know that as soon as motor is turned on there is a sudden spike which enters the circuit from the ground of the load cell which not only gives the false reading but disables the other sensitive devices like mcp2200 .

Please suggest me what to do in this situation .......How is load cell connected in such kind of an application .Is this kind of noise normal (i mean do we use some special technique to keep away the motor noise entering the circuit from load cell body .The noise pattern is consistent whenever the motor is switched on (contactor is switched on).

I am enclosing a screenshot of the image.



I want to keep my circuit free from this motor noise .And i also figured out that it exists only when the contactor is switched on ...... please suggest what could be done , as the circuit uses a high precision 16 bit adc , this noise is not at all acceptable.....


Thanks and regards....
Jitender singh

Hi,
Try with shield wire for Load-cell. Also ground the shield. Keep away the load-cell wire from power cables as much as possible.
Use bypass capacitors for your electronic circuit power supply. Try with several nf range capacitors to get any improvement.
Hope this helps you to get any improvement.

dear dinesh , thx for showing the concern........I removed everything from the power supply now.......wen i just push the contactor manually i can see the noise on the power supply output .......So the problem i guess is the contactor switching ..........Please suggest what can i do to remove the noise which enters the ac power line from the ac motor.....The noise is more while start and stop.......... I dont want the ac motor to affect the power supply which is using 7805,7812,7912 , for generating 5v, 12v, -12v .(using a transformer and a bridge).Though i have used 1000uF at the input of 7805 , 10uF,1uF , 0.1uF at the output or 7805.

But still the noise is able to enter the power supply.....and its quite huge(around 20-40V spike persistent) as soon as contactor is switched on)......Please suggest what could be done.....

Thanks and Regard
Jitender

Do you mean even without motor, when you on and off the contactor only still there is noise ?

motor is connected to the contactor , wen i manually push the tab of the contactor the motor runs creating the noise for other power supplies.........

In one application we ended up using separate sealed lead acid batteries to power a load cell (plus associated circuits) and a DC motor as the only way to remove noise

horace1 said:

In one application we ended up using separate sealed lead acid batteries to power a load cell (plus associated circuits) and a DC motor as the only way to remove noise

Click to expand...

in general then in ac motors there will always be noise ???????????

Hi,

If you google on 'CONTACTOR motor supppressor' you will see there are plenty of Contactor and motor supressors.

They should help the problem.

You can also use one of the many filters on your micros power supply, starting with a filter on the input AC lines down to a filter just before the 5v regulator.

As well as the other methods mentioned above, do not restrict your attention to just the power rails, you can also very easily pick up interference on any long input leads to the micro board with similar failures

Typical examples
https://uk.farnell.com/jsp/search/productdetail.jsp?sku=9520864&CMP=i-9162
https://uk.farnell.com/jsp/search/productdetail.jsp?sku=1191337&CMP=i-9162
https://uk.farnell.com/jsp/search/productdetail.jsp?sku=9526943&CMP=i-9162

hello



The spike seen on your post #1 , with an oscilloscope show high frequency disturbation.( 1µS/div )
so the loadcelle doesn't care with this high frequency.

As recommanded in previous post, you must add filter on the power supply for the MCU , and power suply for loadcell.

Do you have a DC amplifier on the output loadcell signal , before your ADC ?
or direct connection to ADC ?
You must use a LOW PASS FILTER for this kind of signal .. maybe maximum 10Hz !
so analog filter or parameter inside ADC system , or averaging by MCU ..

Do you have "Electronic Earth (Separate Ground) in your factory ?
Because AC leakage current comming from AC motor, Heaters ..etc .. must not pass in the same way as in electronic parts.
It's usual in France to use Electronic grounding , separate from THE main Earth Ground also connected yo every metalic parts.
(sometime difficult to keep realy separated!)

Hi jitender,

I hope there are few more options available,
Use few capacitors in output of 7805 and 7812, with lower values than 0.1uf; you may need to use several of them.

Avoid power unit of transformer and bridge; try to use different type of AC to DC power regulator to power your uC circuit.
You can simply use a computer power unit (ATX power unit) to power your uC; it has +12V,-12V and +5V outputs. They are not sensitive to that type of noise.

Let us know the result.

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Dear paulfjujo ,
we dont have separate electronic ground in india, I am using only the earth ground to connect the machine body to earth.

And the load cell is connected to ad1230 adc 20 bit , via few smd filter components like resistor and cap at the input......

The problem is that when the motor switched on The noise enters the power supply from ac mains and it is seen on the 5V supply whereas the supply for the Microcontroller +adc+usb serial port pcb card is obtained by converting 12V from the meanwell smps to 7805 with adequate input and output capacitors........

Please suggest some ac line filter or any other methos to filter the noise in the power supply......

paulfjujo said:

hello



The spike seen on your post #1 , with an oscilloscope show high frequency disturbation.( 1µS/div )
so the loadcelle doesn't care with this high frequency.

As recommanded in previous post, you must add filter on the power supply for the MCU , and power suply for loadcell.

Do you have a DC amplifier on the output loadcell signal , before your ADC ?
or direct connection to ADC ?
You must use a LOW PASS FILTER for this kind of signal .. maybe maximum 10Hz !
so analog filter or parameter inside ADC system , or averaging by MCU ..

Do you have "Electronic Earth (Separate Ground) in your factory ?
Because AC leakage current comming from AC motor, Heaters ..etc .. must not pass in the same way as in electronic parts.
It's usual in France to use Electronic grounding , separate from THE main Earth Ground also connected yo every metalic parts.
(sometime difficult to keep realy separated!)

Click to expand...

- - - Updated - - -

- - - Updated - - -

Dear dinesh ,
I tried to used several capacitors at the output of the 7805 , little improvements.But still i can c a spike of around 10V when motor switches on.

I used meanwell smps for 12V and then i am using 7805 to convert to 5V . Still there is that much noise , this was new for me........Still working to remove it down to nearly zero......I think i need to make a very special power supply using murata filters and lc filters at the input to remove the noise ......If u have anything in mind do let me know....Thanks for the concern......

DineshSL said:

Hi jitender,

I hope there are few more options available,
Use few capacitors in output of 7805 and 7812, with lower values than 0.1uf; you may need to use several of them.

Avoid power unit of transformer and bridge; try to use different type of AC to DC power regulator to power your uC circuit.
You can simply use a computer power unit (ATX power unit) to power your uC; it has +12V,-12V and +5V outputs. They are not sensitive to that type of noise.

Let us know the result.

Click to expand...

Hi jitender,

What is the smps you used ?
Did you try with computer power supply unit, I positively guess that will solve your problem.
In that case you can avoid 7812 and 7805 also; since ATX power units readily has voltages that you need.

Hello

did you try to install schaffner EMC filter on 230V AC of power supply as wp100 suggested ?

can you try to power you application by a DC battery (maybe 4,5V is enough) to check
the influence of Motor ON ?

How long cable do you have between loadcell and ADC1230 input ?
Shilded cable ?
0V insulated from Ground (Earth) ?

How is made your 12V power supply ?
can you separate REFP + brige power supply from the main 5V DC ?
any Drawing ?


For software application
are you using recommended 10 FPS maxi sample rate.
Don't forget to use averaged value, never instantaneous value, to reject the maximum of noise.

I am going to purchase an AC line filter for filtering the noise from the motor from entering the power supply, i hope it works......

paulfjujo said:

Hello

did you try to install schaffner EMC filter on 230V AC of power supply as wp100 suggested ?

can you try to power you application by a DC battery (maybe 4,5V is enough) to check
the influence of Motor ON ?

How long cable do you have between loadcell and ADC1230 input ?
Shilded cable ?
0V insulated from Ground (Earth) ?

How is made your 12V power supply ?
can you separate REFP + brige power supply from the main 5V DC ?
any Drawing ?


For software application
are you using recommended 10 FPS maxi sample rate.
Don't forget to use averaged value, never instantaneous value, to reject the maximum of noise.

Click to expand...

Computer power units are already equipped with AC filters (they must be otherwise it will burn mother-board chips); practically they are less sensitive to industrial AC noises. Also those power units are not very expensive 1000 LKR (US$ 8)

https://www.youtube.com/watch?v=z2oSFpKh_Uw&feature=related
https://en.wikipedia.org/wiki/Power_supply_unit_(computer)
https://en.wikipedia.org/wiki/ATX

Dear friends ..... i am using the delta ac motor drive which converts single phase to 3 phase for driving 3 phase motor from single phase (using the delta ac drive).
Now i am generating the analog voltage 0V - 10V to vary the speed.....of the drive :
1.generating the 0 - 10V with dac and opamp....
2.these 2 wires go into the ac drive for varying the speed......


The problem is when the motor runs : my circuit which measures the load cell weigh using ads1230, shows a considerable drift even if the weight is not applied....
Surely the motor creates the problem and disturbs the ground due to which i get this problem....
Can someone suggest me the best possible way to drive an ac motor without the motor disturbing the adc counts.......
Some power supply filtering is needed or what ......plz suggest.......