Measuring Electrical noise with a oscilloscope

samvivi7

Lifetime Supporting Member
S
Join Date
Apr 2016
Location
NJ
Posts
50
Hey Guys,

Need a little help measuring electrical noise which is causing our encoder reading to flicker.

i need help setting up oscilloscope to read noise on: -
- signal cable of the encoder.
- 120VAC power
- 24VDC power

it's driving me crazy trying to find where EMI is coming from.
also i have attached of a oscilloscope which is similar to the one we have.
Thanks for the help, :)

Sam

oscilloscope.PNG
 
I am not powering the encoder with 120VAC I would like to test noise on the 120VAC line.
I don't have a model number of the encoder but this one is a positioning one.
 
All encoders let you do positioning... some better than others, but all of them do. Also, for checking noise, it's probably more important to know how they're connected and what type of interface they're using.

Or are you just trying to learn how to use an oscilloscope?
 
is the encoder cable shielded with a drain wire connected to ground in only one location?
is the encoder cable run along with 120 / 240 / 480 wiring? if so, you may want to run a bare ground wire in the duct.

have you checked your plc connections for loose wiring?
is your encoder cable going through any terminal blocks? they can cause an issue.
have you checked any solder joints for a cold solder connection? they can act as antennas.

just my thoughts,
james
 
James Mcquade said:
is the encoder cable shielded with a drain wire connected to ground in only one location?
is the encoder cable run along with 120 / 240 / 480 wiring? if so, you may want to run a bare ground wire in the duct.

have you checked your plc connections for loose wiring?
is your encoder cable going through any terminal blocks? they can cause an issue.
have you checked any solder joints for a cold solder connection? they can act as antennas.

just my thoughts,
james
Click to expand...

Yes, the cable is shielded.
i have the cable running outside away from everything.
PLC wiring looks good.
 
Does the system use one or more VFD's?

If so:
- Is filtering applied on the VFD?
- Is properly shielded power cable used from VFD to motor?
- Is the encoder cable running anywhere near the the motor cable?
 

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