Author Topic: How do I get the resitance of the DCA ranges?  (Read 663 times)

0 Members and 1 Guest are viewing this topic.

Offline ballsystemlordTopic starter

  • Regular Contributor
  • *
  • Posts: 248
  • Country: us
  • Student
How do I get the resitance of the DCA ranges?
« on: October 26, 2023, 03:15:49 am »
Hello,
Often higher end meters specify the burden voltage of the amps range. For example, 100mV/mA would give us a 100ohm resistor. But some meters only list the voltage drop as a < X.XXX number. Like the attached image.

How do I get/approximate the resistance of the meter's amperage ranges?

Thanks!
 

Offline bdunham7

  • Super Contributor
  • ***
  • Posts: 8175
  • Country: us
Re: How do I get the resitance of the DCA ranges?
« Reply #1 on: October 26, 2023, 03:49:11 am »
Ohms law, R=V/I.  So the 10A range states "<0.5V", 0.5/10 = 0.05, that implies the resistance is 0.05 ohms or less.  The total resistance includes more than the shunt--there's the internal circuitry and the fuse.  That range likely has a 0.01R shunt.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline ballsystemlordTopic starter

  • Regular Contributor
  • *
  • Posts: 248
  • Country: us
  • Student
Re: How do I get the resitance of the DCA ranges?
« Reply #2 on: October 26, 2023, 04:25:04 am »
I figured ohms law was the way to go, but 11mV burden on 1nA seemed a bit high.
 

Offline bdunham7

  • Super Contributor
  • ***
  • Posts: 8175
  • Country: us
Re: How do I get the resitance of the DCA ranges?
« Reply #3 on: October 26, 2023, 04:31:23 am »
I figured ohms law was the way to go, but 11mV burden on 1nA seemed a bit high.

The burden voltage shown is the maximum at full range.  At partial range readings, it should be proportionately less if it is using a regular shunt system.  If it is an active system, then the input can't be characterized as a resistance.  This meter likely uses a 100R shunt for the low current ranges and a gain amplifier for the very lowest.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf