I was surprised to connect leads of multimeter in parallel to a series circuit and measured the same Ohm's law calculated amperage. Is this the possible or I am I missing something? I learned that to measure amperage with multimeter the meter needed to be in series with the circuit.
Multimeter ammeter in parallel
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jbelectric777
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Not impossible, depends what you were measuring and the calibration of your meter, why dont you provide a schematic of the load and where you placed your leads, Im curious.:-?
When you place an ammeters leads across a component, you are basically shorting out that component. (An ammeter has very low resistance.)
The only way you will measure the calculated current is if the source resistance is very high compared to the resistance you are measuring across.
For example, assume a 120V circuit with a 120 ohm light bulb and a dimmer switch that goes from 0 ohms to 10K ohms.
Set the dimmer switch at 10K ohms, the calcualted current is about 120/10000. The light bulb resistance is small enough to ignore. Put your ammeter across the light bulb, and you will measure the calculated current.
But if you set the dimmer switch to 0 ohms, and now if you put the ammeter across the light bulb you will let lots of smoke out of the meter (and maybe even some flames!!!).
Before we insert the meter, the current is 120V/120 ohms = 1 amp. The source resistance is basically 0. If we put the meter across the light bulb now, it will basically short out the voltage source. The meter will peg as the amps go very high.
So in general, one should be very careful with an ammeter. You should always break the circuit and insert it in series. And never "cheat" the ammeter fuse by jumpering the leads.
Steve
The only way you will measure the calculated current is if the source resistance is very high compared to the resistance you are measuring across.
For example, assume a 120V circuit with a 120 ohm light bulb and a dimmer switch that goes from 0 ohms to 10K ohms.
Set the dimmer switch at 10K ohms, the calcualted current is about 120/10000. The light bulb resistance is small enough to ignore. Put your ammeter across the light bulb, and you will measure the calculated current.
But if you set the dimmer switch to 0 ohms, and now if you put the ammeter across the light bulb you will let lots of smoke out of the meter (and maybe even some flames!!!).
Before we insert the meter, the current is 120V/120 ohms = 1 amp. The source resistance is basically 0. If we put the meter across the light bulb now, it will basically short out the voltage source. The meter will peg as the amps go very high.
So in general, one should be very careful with an ammeter. You should always break the circuit and insert it in series. And never "cheat" the ammeter fuse by jumpering the leads.
Steve
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