FPGA → RT: Short‑Circuit / Overload Current Waveform

[Abhi14ry]

Hello everyone,

I am working on an FPGA + RT application based on NI FPGA–RT streaming examples and would like some guidance.

Setup

• cRIO-9045, NI‑9223 AI0 on FPGA
• Input: sine wave from function generator (real application will use a current probe)
• FPGA loop rate: 4 µs (real application loop speed is 4 µs )
• Data streamed via DMA FIFO to RT

What I Am Seeing

Following the NI example codes, I consistently receive a clean sine wave on the RT side. This confirms that FPGA acquisition and FPGA→RT data transfer are working correctly.

What I Want to Achieve

My actual application is a thermal short‑circuit test (1–5 s duration).
I want to obtain a waveform similar to the attached image: a short‑circuit / overload current waveform with very steep, narrow current peaks (high di/dt), not just a smooth sine wave. When Thyristor trigger(switch ON), start obtaining graph, when OFF graph goes to zero. The attached image is also sine wave with 50Hz frequency obtain from High Voltage AC via current probe.

[GerdW]

Hi Abhi,

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@Abhi14ry wrote:

What I Want to Achieve

My actual application is a thermal short‑circuit test (1–5 s duration).
… When Thyristor trigger(switch ON), start obtaining graph, when OFF graph goes to zero. The attached image is also sine wave with 50Hz frequency obtain from High Voltage AC via current probe.

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You need to implement your requirements in code!

What is your actual question? What is the problem?

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@Abhi14ry wrote:

I want to obtain a waveform similar to the attached image: a short‑circuit / overload current waveform with very steep, narrow current peaks (high di/dt), not just a smooth sine wave. 

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Then you need to measure the correct current line: do you?

You also need a current sensor that allows for high frequency measurements…

[Abhi14ry]

What I want is the data acquisition and display to start only when the trigger is ON and stop when it's OFF, essentially compressing the graph to show only the triggered portion rather than continuous data flow. Right now when I am pressing Trigger, I am getting this big sine wave flowing continuously.

[GerdW]

Hi Abhi,

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@Abhi14ry wrote:

What I want is the data acquisition and display to start only when the trigger is ON and stop when it's OFF, essentially compressing the graph to show only the triggered portion rather than continuous data flow.

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Then you need to change the VI according to that requirement!

• What about collecting data in the array as long as the "trigger" is true?
• What about using a shift register to hold the collected data?

These are basic programming steps in LabVIEW: I guess you took the basic learning courses?

[GerdW]

Hi Abhi,

btw one question: why do you use the FPGA interface when you could use DAQmx instead?