What is the problem for the turn-off measurement?

[sschang]

Hi, 

  I have a labview problem for measuring the turn-off current transients as attachment. It does not work to load the turn-off transient current waveform in the  "turn-ff transient current waveform", and always load this waveform in the "current waveform" when the appliance is turned off.

It is appreciated to answer the problem.

sschang

[kartiknattar]

Well that's because your trigger level is lesser than the high state level. you should consider increasing your trigger level

[sschang]

Hi, kartiknattar

  Many thanks for your response.

I do not clearly know what do you mean. Does it change the Comparison Functions from "greater" to "less"? Can it detect the turn-off current waveform if the setting value of trigger level is greater than the high state level (Vm) when the appliance is turned off by me? It should be not.

 My problem is the turn-off waveform always be showed in the "current waveform" not in the "turn-off  transient waveform" when the appliance is turned off by me. Also, I can not save the "turn-off waveform" in the Excel file.

It is appreciated for your answer.

sschang

[kartiknattar]

I have checked your code by simulating a sine wave signal. The code is working fine. As long as your trigger level is greater than VM the data will be saved.

[sschang]

Hi, kartiknattar

  Many thanks for your help.

The code is the same as the last for the turn-off appliance. The code is attached with the message for your reference.

I can see the turn-off waveform in the upper window "current waveform" when the appliance is turned off by me and the trigger level value > Vm. However, the turn-off waveform should be shown in the bottom window "turn-off transient waveform" for saving in the excel file.

The upper window is a real-time waveform recorder, and the bottom window is an event recoder. 

How does the code change for saving the turn-off transient waveform of an event in the bottom window?

Best regards

sschang

https://drive.google.com/file/d/1n2i5yfxMTNsKHbO4N__L80Rw_zxaSF8K/view?usp=sharing 

[sschang]

Hi,  kartiknattar

   Indeed, the trigger can be done when the value of the trigger level is greater than Vm.

But, That is not I want. I need an event trigger when the appliance is turned off by me.

  The value of Vm will decrease when the appliance is turned off. The trigger should be started when the value of Vm is less than the value of trigger level set by me. The transient waveform of turn-off event should be shown in the down window (Turn off transient waveform).

  My problem is the transient waveform of turn-off event is shown in the upper window (current waveform). Why?

   Do you have any solution?

It is appreciated for your answer.

sschang

[RTSLVU]

Instead of trying to "catch it", trigger on something more reliable like whatever is turning off the power.

I have done similar tests using an Oscilloscope and trigger on the power off event. For instance one test uses a relay to open the AC line of the UUT. I trigger the scope on the relay coil. Another test uses a programmable AC power supply to capture turn off at 1 degree phase increments. I use the scopes "smart trigger"to trigger on the AC dropout (trigger if no cycle within 20mS) as we also test 50Hz products.

I have use NI-Scope and know that is has several "smart trigger" types, I am not sure about DAQmx or whatever you are using for your DAQ

[sschang]

Hi, RSTLVU

   Thanks for your reply.

I do not need an external trigger. It is important to me for the internal trigger of the power current signal from the appliance.

Best regards

sschang

[mcduff · Accepted solution]

Not sure exactly what you want to do, but don't use the high level value for your off trigger. Your waveform has multiple points below that level so it does not make sense to turn it off when the signal goes below that level.

I suggest you measure the RMS value, not peak-to-peak, and monitor that value for your OFF trigger. When the RMS is less than a certain value then that would be you OFF trigger.

You will need two trigger values, or just use the RMS value. Above a certain threshold case 1, below case 2.

[sschang]

Hi,  mcduff

   Many thanks for your suggestion.

sschang