I think the title is revealing. I'm planning to use 2 multi-meters to get a better perspective of my circuits. Is there any drawback in this situation i should be aware?
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4 Answers
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Yes, that works. However, keep in mind that no meter is perfect. Ideally, voltmeters have infinite impedance and current meters 0 impedance. Real ones don't, of course.
To the extent the meters aren't perfect, particulary the current meter, it will affect the system while trying to measure it. The current meter will cause some voltage drop proportional to the current. You have to be aware of this and possibly account for it. For example, if the voltage drop across the current meter is too big to just ignore, you have to consider carefully on what side of the current meter you measure the voltage, and whether your system can tolerate the voltage drop in the first place.
answered Jul 22, 2016 at 23:33
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2\$\begingroup\$ Unless the ammeter is really crummy or the current level is really high, there should be no measurable interference between the two meters. \$\endgroup\$ Commented Jul 23, 2016 at 0:39
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\$\begingroup\$ The higher end multimeters are actually worse for measuring current in ELV system because they use fuses that have higher safety ratings but also higher resistance. Often it's better to add a resistor of your chosing to the circuit and use the multimeter in voltage mode (this also has the advantage that you can remove the multimeter without breaking the circuit). \$\endgroup\$ Commented Jul 23, 2016 at 3:12
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\$\begingroup\$ "real voltage meters aren't perfect" - I would put a mosfet voltage follower to both inputs. Where does that put me? \$\endgroup\$ Commented Jul 23, 2016 at 5:00
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3\$\begingroup\$ It would be more n00b friendly to spell out that the current taken by a voltmeter is unlikely to alter the current reading. The voltage drop on an ammeter is likely to alter the voltage reading. So choose connection points appropriately. \$\endgroup\$– Neil_UKCommented Jul 23, 2016 at 5:41
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\$\begingroup\$ @Neil_UK please make that an answer. \$\endgroup\$– winnyCommented Jul 23, 2016 at 8:04
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Yes, you can. No real draw back unless you get to very small fractions of a volt or micro amp ranges and your precision requirements are tight. Or very high voltages and currents that your multimeter wasn't designed to handle well.
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Bear in mind we're assuming digital voltmeters here, an analog meter will have an ohms per volt characteristic (google is your friend if you don't understand this).
Digital meters usually have a fixed impedance but this value will dependly largely on the quality (and price) of the meter.
I agree about probe fuse resistances being high, stick the meter onto ohms and short the probes, on mine it's about 8 ohms.
answered Jul 23, 2016 at 11:47
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I don't think it is a big deal, you can use. But calibration matters before you taking the reading. Do it couple of times. So you can stick to the precise value
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2\$\begingroup\$ (1) "But calibration matters ...". Explain how the OP could calibrate. (2) "Do it couple of times." Explain why. (3) "So you can stick to the precise value." What does this mean? Welcome to EE.SE but be aware that poor answers can get voted down. \$\endgroup\$ Commented Jul 23, 2016 at 8:47