basic capacitor reading using multi meter help

Thread Starter

a Rob

Joined May 14, 2017
151
i have capacitors on the board and reading it direct by touching it with multi-meter wire.

4.7 uf , 400v cap
reading = 09.52

is this right ?
 

Reloadron

Joined Jan 15, 2015
6,129
First, most capacitors average a wide margin of allowable error, numbers like 20% are not unusual. Next you are measuring a component in circuit so that component likely has other components in parallel with it. What it amounts to is you can't measure a 4.7 uF capacitor in circuit and expect to see even c;lose to 4.7 uF. The same would be true of resistors and inductors as well as other components .

Ron
 

ErnieM

Joined Apr 24, 2011
8,183
Readings of components in circuit are rairly meaningful, except in some special cases like when the parties a dead short.

Even then the short could be caused with something else in parallel with the component.
 

Reloadron

Joined Jan 15, 2015
6,129
What part of you can't measure components in circuit did you not understand? Get familiar with the rules for capacitors in series and parallel, then the same for resistors and inductors and .... You can't measure the value of components in circuit. Then, if you do, the numbers you get are not only meaningless but will depend on the circuit.

Ron
 

Reloadron

Joined Jan 15, 2015
6,129
When you think about it things will make sense. If you can get a few components, just bare bone components, try and measure them out of circuit and see what you get.

Ron
 

Thread Starter

a Rob

Joined May 14, 2017
151
1: so it is best to test components out of the board to get accurate reading ?.
2: in case of parts being blown and number marks cannot be read how do u then determen what value it was so that we can replace it with good part.
 

Reloadron

Joined Jan 15, 2015
6,129
1: so it is best to test components out of the board to get accurate reading ?.
2: in case of parts being blown and number marks cannot be read how do u then determen what value it was so that we can replace it with good part.
1. When possible you work from a good schematic or drawing which identifies the parts.
2. Last resort is an educated guess as to what the part was and the value.
3. Yes, for the most part you want to check components out of circuit. There are ways to check some components in an active circuit (energized circuit) but that comes later.

Ron
 
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