Why Big Capacitor Inside Multimeter?

It does the exact same thing every other capacitor does. It causes the current flowing through it to lead the voltage across it.

Now if you wish to know how this affects the components connected to this capacitor, then you must trace the circuitry connected to the capacitor and identify the components connected. I recommend making a hand drawn schematic to aid in the circuit analysis.

This capacitor appears to be a polyester capacitor. I would guess that it would be close to a micro-farad in value.

Thanks for reply. I admit to being a bit lazy and not tracing out circuits but one excuse I have is that a gave the meter away to a young physics whizz after I took the photos. I just thought someone might know right off why its put there and might be able to say "oh yes, it limits the floop going to the flop" . Thanks for identifying it as polyester and its aprox value I did not that.

It prevents the clock frequency from returning to the battery, there by preventing formation of interfering current loops, with other circuits on the PCB.

Fantastic answer. Why do they make it so big? Why not just use some small electrolytic to do the job? Thanks

I am sorry, that my answer is considered offencive. Yes, electrolytic will do similar job, but for a much lower frequency range.

Not considered offensive at all. You might misunderstand the word fantastic.

Thank you, Tank Circuit.

I'm not convinced that this is a supply decoupling capacitor as Joshi stated, but it could be. Electrolytic capacitors particularly of the 80's era have lousy high frequency characteristics and very poor accuracy tolerances. Many small electrolytic capacitors often have a ±20% tolerance. Polyester or mylar (the other possible type of that package style) capacitors will nominally have less series parasitic resistance and inductance characteristics than an electrolytic. Thus they will operate at higher frequencies as expected.

Thankyou redfred , a few things there I did not know.

My old Beckman multimeter measured voltage, current, frequency, capacitance, and some diode and transistor parameters. Big Red could be a "reference" capacitor for the larger scale(s) of the capacitance measurement function. Need more information like a circuit trace or actual schematic.

This is the Beckman DM10 which is really basic. I does volts,ohms,amps, diode test and thats it. Thanks for your input.

It's for AC coupling when measuring mains voltages.

(just a guess)

That is a good guess. It would have been positive, had the capacitor been placed close to socket of the prod.

Thankyou Electroman. My guess is you are right and your explanation covers why its so big.

It could be for the AC input to eliminate DC from the circuit. I have a VOM from the 1960's. The capacitor must be non-polarized, and high voltage to withstand DC that might be present. Vacuum tube equipment had 600 volts DC typical. A larger value will give you more signal from lower frequencies, i.e. better frequency response.

Good guess, those VOMs used to have an additional scale called "output" and showing dB (dBm) directly. The capacitor was similar to the one described.

Lots of time has lapsed for this thread but here are details.

This capacitor is generally Polypropylene for low leakage for pA input current source and also operates at reasonable high frequency and good pulse current response specially used for dual slope ADC input stage or charge sampling stage like ICL7135 etc.

Polyester capacitor will also work to near to Polypropylene capacitor with increased error. PTFE capacitors are the best but they are very expensive. Capacitor value is of the order of 0.1uF to 1uF and normally higher voltage from 400V to 2000V.

If you replace these capacitors with other capacitors of low frequency response and of high leakage and of high residual charge then ADC will have lots of error.