Multimeter notes: Difference between revisions
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Not a standard feature, because it needs some faster processing to do. | Not a standard feature, because it needs some faster processing to do. | ||
There are a few methods | |||
That said, it's useful to do at all even if the error is higher, so some off-brand multimeters do it anyway. | |||
You may also want to measure the capacitor's equivalent series resistance (ESR), | |||
because an increasing, or higher, or increasingly temperature-dependent{{verify}} | |||
ESR tends to indicate an aging capacitor. | |||
...or more practically, you often look at a table (or plot) of "this capacitance-voltagerating combination should have no more ESR than X" | |||
Most standard multimeters, even the more expensive ones, ''don't'' do this, | |||
presumably because it's a bit of a specialization | |||
and takes more time so takes away from the "multimeter gives you immediate figures" uses. | |||
There are a few methods of measuring capacitance. | |||
https://electronics.stackexchange.com/questions/441383/how-do-digital-multimeters-measure-capacitance | https://electronics.stackexchange.com/questions/441383/how-do-digital-multimeters-measure-capacitance | ||
You might already have thought of the capacitor's t=RC. | |||
This means that with a known resistance, we can charge it to the , and monitor the voltage, and fill in C=t/R | |||
You generally cannot test in-circuit (you would end up measuring the largest capacitance between the points you hold to, which you often cannot know is corect), | |||
but there are some | |||
At ''very'' low capacitance you are instead limited by measuring speed/precision. | |||
Some multimeters refuse to go down to picoFarad, | |||
probably also for the reason that by then you're also measuring the wires and even the meter's PCB, | |||
so even if the value shown is accurate we shouldn't pretend it is necessarily all that meaningful. | |||
Limitations: | |||
However, '''the larger the capacitance, the longer it would take to get to the actual would take''' | |||
: At low capacitances we would call that rise time, but if you use the same resistor for millifarads or larger you're looking at minutes or hours to get a reasonable charge | |||
Multimeters may do that, but with a fixed current to make life easier. | |||
They also use a fixed time, rather than waiting for the RC. | |||
That ''does'' limit the precision, | |||
but also it doesn't spend that much of the battery. | |||
If you want an answer ''quick'', you start looking at expensive RLC meters. | |||
If you can accept a slower answer you can do it much cheaper. | |||
https://www.circuitbasics.com/how-to-make-an-arduino-capacitance-meter/ | |||
You can even do a chirp and see what kind of filter it's being, | |||
but this doesn't seem like it's precise without taking more time either. | |||
In-circuit, they will tend to measure the largest capacitance, which is only sometimes the capacitor you're holding it to. | |||
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