Frequency Inverter output waveform using oscilloscope

Thread Starter

Lemon_Foam

Joined Sep 18, 2017
40
Hi All

I have a Keysight brand oscilloscope model: DS0-X 1102G.
I wish to measure the output waveform from my Schneider brand Frequency Inverter model: ATV320U15N4C

When i turn on my Frequency inverter, the output current and voltage waveform is expected to be as below.
i) Yellow color is voltage output waveform (PWM signal)
ii) Green color is current output waveform (Sinusoidal Signal)
1716455179785.png

I can get the green color current waveform as expected, but I face a problem on getting the yellow color PWM voltage waveform using oscilloscope

Can anyone tell me that is is any setting or tunning on my oscilloscope (DS0-X 1102G) i need to do, so that can read an expected PWM Voltage output waveform of Frequency Inverter.

Thank You
 

nsaspook

Joined Aug 27, 2009
13,567
Try using a single/falling rising trigger on your pwm waveform channel to freeze a scan and adjust the H speed and position until the stopped signal is suitable for frequency measurement.
 
Last edited:

Irving

Joined Jan 30, 2016
4,065
On my 4-channel Siglent scope I'd set a trigger on the PWM as a pattern of a falling edge at +2.5v followed by another falling edge at -2.5v (using 2 channels) - this will capture the + to - transition. I'd then add a trigger delay to examine the PWM at any point in the following cycle
 

MisterBill2

Joined Jan 23, 2018
19,461
You will need to use a much faster sweep speed to see the PWM waveform. AND you will need to trigger the sweep from that channel. THAT will allow you to observe the PWM quite well.
 

nsaspook

Joined Aug 27, 2009
13,567
You will need to use a much faster sweep speed to see the PWM waveform. AND you will need to trigger the sweep from that channel. THAT will allow you to observe the PWM quite well.
I have the exact same scope at work. It will autoset to a good and stable display if the PWM duty rate is fixed or the modulation index is low.

High modulation index PWM waveforms are much tricker to get stable displays.
One of my general ESC/Inverter PIC32MK boards programmed for 5000Hz PWM to 400Hz quadrature power output for driving old synchro-servo motors. Looking at the output of one half-bridge to a not so good RC filter for the 400Hz signal display on the scope.
1716651023159.png
1716651178637.png
 

MisterBill2

Joined Jan 23, 2018
19,461
OK, now for the serious question: WHAT parameter of the output wave form do you need to measure, and how accurately do you need to measure it. Accurate measurement of frequency is a challenge with less expensive digital scopes, because the sample rate it not nearly fast enough, That is simple to verify by looking at the display. The shapes of the waves vary because not enough samples are taken.That is a basic limitation of less expensive digital scopes. An adequate ANALOG scope does not have that limitation, but it does suffer from other limitations.
So once again,exactly what property of the waveform do you want to measure, and how accurately do you need to measure it??
Also, the TS states that the green trace is the current waveform. Just how is that waveform being measured?? I am asking because often obtaining a current wave form requires a fair amount of effort.
 
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