Digital Multimeters (DMMs) and Precision DC Sources

cancel
Showing results for 
Search instead for 
Did you mean: 

Instrument Accuracy | DMM Vs SMU | Voltage Measurement

Hi Engineers,

 

I have a question on instrument accuracy. Could someone help me in understanding how to choose a instrument for the below DC Voltage Regulator voltage measurements.

 

Typical O\P voltage of regulator at no load = 5V.

Load Regulation (0 to 100mA) is 0V to 0.05V

 

I wanted to measure the o\p voltage of a regulator. I can either measure using SMU (0.02% + 200uA Accuracy at 6V operating range) or DMM( Six and Half digit). As we already know DMM gives more accurate and precise measurement. But do I need that much accuracy for the above measurements? (Yes or No: Please provide the reason)

 

0 Kudos
Message 1 of 6
(2,619 Views)

SMU = SOURCE Measure Unit.  You are not measuring the input voltage of the device (ie the power you are sourcing into the device); you are measuring the output of the regulator.  Therefore, a DMM is the device you should be using.


GCentral
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
Unofficial Forum Rules and Guidelines
"Not that we are sufficient in ourselves to claim anything as coming from us, but our sufficiency is from God" - 2 Corinthians 3:5
0 Kudos
Message 2 of 6
(2,615 Views)

We can set a SMU to Source Current mode with the below settings and measure the voltage. Can you explain in more detail on why we shouldn't use SMU to measure voltage.

 

O\P current = 0A.

Voltage Range and Compliance = Voltage to be measured + 1V 

 

 

0 Kudos
Message 3 of 6
(2,565 Views)

@Incognito_Guy wrote:

Can you explain in more detail on why we shouldn't use SMU to measure voltage?


An SMU is a basically a power supply with very accurate measurements on its output.  It is not designed to measure the output of other devices.  You should be using a DMM.


GCentral
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
Unofficial Forum Rules and Guidelines
"Not that we are sufficient in ourselves to claim anything as coming from us, but our sufficiency is from God" - 2 Corinthians 3:5
0 Kudos
Message 4 of 6
(2,556 Views)

Sounds like a perfect application for an SMU to me.  Not only is it accurate enough to measure the output voltage of "5V typical," it can also provide the 100mA load to check the load regulation.  Remote sense should be used for the load regulation test to ensure you're not just measuring the resistance of the connecting leads.

0 Kudos
Message 5 of 6
(2,548 Views)

You can go with either DMM or SMU. There are advantages and disadvantages to both approaches.

 

DMM

  • High accuracy and resolution
  • Measure only voltage or current at a time (on one DMM)
  • One PXI slot per DMM

SMU

  • Limited accuracy and resolution (relative to DMM)
  • Measure current and voltage simultaneously
  • Can act as a load by sinking current
  • High density (number of channels per PXI slot)

 

From my experience with both silicon validation and production testing,

  • DMM is used in cases where SMU is not available
  • For LDO/Regulator testing very high accuracy or precision is not required compared to precision ADC/DAC and voltage references
Santhosh
Soliton Technologies

New to the forum? Please read community guidelines and how to ask smart questions

Only two ways to appreciate someone who spent their free time to reply/answer your question - give them Kudos or mark their reply as the answer/solution.

Finding it hard to source NI hardware? Try NI Trading Post
0 Kudos
Message 6 of 6
(2,525 Views)