Electronics > Metrology

Measuring current

(1/3) > >>

danolteanu:
Hi,
I have a question regarding the indication on A and mA scale of multimeters.
I have a circuit with a 2.5V DC baterry and a 15.1 ohm series resistance.
When I measure the current in this circuit on 10A scale the indication is 0.164A and on 400mA scale the indication is 145mA.
This indication is the same an 3 multimeters I have (Fluke 87V, UT71E and DT9207A).
I thnik the fact is related to the different shunt resistors of multimeters on scale A and mA but do you think it's right for a multimeter to indicate with so much difference on these scales?

thank you
BR/Daniel

jonpaul:
current shunt has resistance depend on range, see specks of the meter.

Use Ohms law to predict results


Jon

danolteanu:
Hi Jonpaul,
I've measured the shunts, and according to the Ohm law with the multimeter in circuit the indications are correct. :)
But I was wondering if all multimeters befave the same?

BR/Daniel

IanB:
Mostly they do all behave the same way. This is not unique to the particular meters you have.

ejeffrey:
You can watch Dave's many videos on current measurement burden voltage and his microcurrent project which uses a very small shunt resistor to minimize this.

There are other techniques that can reduce this further, such as using hall sensors or transimpedance amps, but those have disadvantages that make them not suitable for general purpose multi meters, and you can't eliminate resistance entirely.

Navigation

[0] Message Index

[#] Next page