Digital Multimeters (DMMs) and Precision DC Sources

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Amplitude Measurement of CAN signal

 

Hi,

 

I have an Analog Card 4304 with 32 channels and Max sampling rate of 5 kS/s.

I have to measure the Voltage for CANH and CANL Dominant and recessive, my baud rate is 500000.

 

My question is How can I measure CANH and CANL voltage as the signal frequency is far more than the sampling rate. If not what shall i do to measure these voltages accurately? I also have a DMM 4080 with 1.8MS/s isolated digitizer.

 

Please provide inputs.

 

Thank you

 

 

 

 
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You are looking to achieve the functionality of an oscilloscope in a PXI Analog input module. The 4304 is intended for Power analysis application that requires high resolution (24-bit) and not a lot of digitizing speed.

 

Since your signal is 500kHz, the only option you have now is to use the DMM 4080 in digitizer mode at 1.8MS/s either measure the differential voltage across CANH and CANL or use a switching circuit to measure single-ended CANH in one run and CANL in the next run.

-Santhosh
Semiconductor Validation & Production Test
Soliton Technologies
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Thank you for the response.

 

I am currently trying it out with DMM 4080.

Although it has a digitizer, I am not able to set a triggered measurement. I want to measure the voltage at CANH or CANL on Dominant and Recessive levels. With the DMM I am able to measure the voltage but since it is not triggering properly I am not able to measure the exact Dominant and recessive voltages for CAN_H and CAN_L. I have attached the example for when exactly I have to take the measurement.

Even though the DMM sampling rate is high almost 4 times the Nyquist rate why I am not able to trigger.

 

Any Idea for that?

 
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As already stated, what you're looking for is an oscilloscope with advanced triggering features.

 

DMM has only a handful of triggering options and none of those is to trigger on a voltage level on the measurement leads.

 

Your options,

  1. Capture long enough waveform that covers both recessive and dominant state and extract measurement using post-processing
  2. Find a way to send a trigger right at the recessive or dominant state over the PXI_Trig bus to the DMM
  3. Trigger the CAN communication and DMM at the same time, configure Trigger Delay of DMM to be the time taken for the CAN signal to reach recessive or dominant state (only possible if your CAN communication device can be trigger and deterministic)

 

It is just that all that you have is a plier instead of a hammer but you want to hit the nail harder like a hammer, you could do only so much with what you have.

-Santhosh
Semiconductor Validation & Production Test
Soliton Technologies
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