Noise issue in measuring current from dc motor through current sensor!!!

Status
Not open for further replies.

siva88

Newbie level 4
Joined
Jul 12, 2013
Messages
6
Helped
1
Reputation
2
Reaction score
1
Trophy points
3
Location
chennai,india
Visit site
Activity points
51
Hi everyone,

I am working on a project where I control PMDC motor by switching on/off through mosfet (PWM control) by DSP controller, also I measure real-time current of the motor using LEM (LTS-15-NP) current transducer.

Well, the problem is I get noise in the current sensor output line when the PWM(or switched voltage) is given to the motor!!:sad:.

While the motor is turned-on the input voltage to the current sensor picks-up noise(see the below scope image).:???:
The output voltage of the current sensor has also have the same level of noise.


I also had a doubt that there could be some switching noise (some kind of transient peak current in the motor line while switching)!!. So I have measured the line current (while running) by putting a SERIES RESISTOR and measured with a scope, and it doesn't look like it has noise in the line.:|(below is the scope image for line drop voltage).


The ultimate problem is when I read this values through ADC, and plot the current graph all I get is some jumpy values so I do some software low pass filter, but still I have some noise, due to which I can’t able to interpret actual rise in current.

Instead of getting a “almost steady current “ I get some “jumpy steady current” which gives me lot of issues!!!:-x

Series resistor and some calculation:

Resitor = 0.5E

Voltage = 0.366v

Current(I) = 0.732A

Additional details FYI:
Motor = 180vdc PMDC motor.
Switching freq = 10Khz
Control: PWM control.

Added the circuit, It's not in full detail but I hope this will be of some help!!


If you can suggest or give an opinion on this, it will be of great help.
Thanks in advance.
 

Thanks frank.I will sure check that, also I was more hoping on suggestion for the current sensor part like some filter circuit or fundamental mistake in the circuit etc.But anyways like you said there could be some noise induced by the brushes too.I will check on your suggestions.
siva
 

Status
Not open for further replies.

Similar threads

Cookies are required to use this site. You must accept them to continue using the site. Learn more…