Multimeter question - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: January 26, 2020, 07:17:43 am
content: Ok I’m almost embarrassed to ask this.I have a fluke Multimeter and I want to check Ma on a dc circuit. Before I try it and screw something up I figured I would ask. Do I lift one end of the component and place the leads in between the component and circuit? Not exactly sure how to do?

author: rstofer
author_rank: Super Contributor
timestamp: January 26, 2020, 07:26:14 am
content: Yes, to measure current flow through a circuit, the meter needs to become part of the circuit. So it needs to be in series with whatever is being measured.If you're lifting a resistor, consider getting the current by measuring the voltage drop instead. No need to lift one end.

author: AVGresponding
author_rank: Super Contributor
timestamp: January 26, 2020, 09:11:22 am
content: It's worth mentioning that measuring the voltage drop across a resistor and using Ohm's Law to calculate the current can often be a far more accurate and precise method than using the meter's built in current measurement (though this does depend on knowing the resistance to a good degree of accuracy and precision).

author: Crambone
author_rank: Frequent Contributor
timestamp: January 27, 2020, 12:33:05 am
content: AWSOME thanks guys

author: Shock
author_rank: Super Contributor
timestamp: January 27, 2020, 08:03:41 pm
content: The most important thing absolute beginners should be aware of is a multimeter in current/ammeter mode is like a low resistance wire - it's essentially short making device. So think whenever you attach it, am I going to short something out? Would you stick a wire across a battery, nope that would be dumb.So if you put the leads directly between a voltage rail and ground or live and neutral (like you normally measure voltage) you will discover how much current the device can supply and how much current your meter leads, meter and fuse can withstand without blowing.If you a lucky just the fuse will blow. In the case of mains electricity your probe tips and fuse will likely violently blow and if using a cheap meter kiss it goodbye. If you short out where a component was, a higher current flows now in that part of the circuit so damage may also occur or blow your meters fuse.The next thing to be aware of is a quick check that there is no high current load or short that exceeds the fuse or multimeters range rating. If you have a faulty circuit and it's blowing fuses or components the easiest rule is don't use the ammeter, we know there is a current problem there already.To verify a circuit here is a simple example, a current limiting resistor and a diode are in series with a battery. Measure the *voltage drop* across either side of the resistor and then across either side of the diode. If you see two voltage drops that add up to the supply voltage and it makes sense, in that circuit you have no shorts. As mentioned at this point you can also use the ohms law method.Avoid using the multimeter in current/ammeter mode to test how good a short is. That can be done with the voltage drop method or with circuit properly isolated from power and denergized and tested for shorts with the resistance/ohms mode or continuity, or across semiconductors with the diode mode etc.Try to use the multimeters highest current range before the lowest current range. Otherwise if you misjudge the circuit current and go straight for the uA and mA range you may also blow a fuse.The only correct way to use the ammeter is in series (inline) with the circuit/component(s).

author: AVGresponding
author_rank: Super Contributor
timestamp: January 27, 2020, 08:10:45 pm
content: Well the OP mentioned measuring mA in a DC circuit, and asked if they needed to lift a component leg.Measuring current in an AC line shouldNEVERbe done by anyone who does not know exactly what they are doing; mistakes here can be fatal.

author: Shock
author_rank: Super Contributor
timestamp: January 27, 2020, 08:20:34 pm
content: Well I think we can assume if your probe tips will violently blow you can imagine what will happen to your little pork sausage fingers if you start including them in mains voltage experiments.