[SOLVED] precision capacitor replacement circuit

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Is there a circuit which acts as a very precise capacitor within a few micro farads range at 1-2% tolerance?
 

Hi,

It depends on frequency range, current range and signal waveform.

Why not buy a 1% tolerated capacitor?

Klaus
 
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What's against using real capacitors? Foil and film capacitors can have good long term stability and low temperature coefficient, you probably need calibration to get rid of the initial tolerance.
 
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Frequency is 8hz I only found 2% and I'm willing to go the extra part count for 1% tolerance.
 

Zak28 said:
Frequency is 8hz I only found 2% and I'm willing to go the extra part count for 1% tolerance.
Click to expand...

What value capacitor are you looking for?
 
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Kajunbee said:
What value...
Click to expand...

1-2uf is fine, I looked into whats called a capacitance multiplier incorporated with oamps and I would not have made this topic had the circuit been absent of capacitors, how ever it would work if the capacitor it uses can be really small since small caps can be made quite precise. I made this topic because I am looking for anything but that circuit.
 

Hello Zak28,

1-2uf is fine
Click to expand...

I don't understand???
You want the tolerance to be within 1%, but you don't really care about the value on what you
actually want.
You also didn't specify what type of capacitor you desire. i.e. Electrolytic, MKT, Ceramic etc.
Also, what voltage rating?
You can obtain Silver Mica types which are 1% rated@500V, but their values don't go higher
than 1000pF (1nF or 0.001uF).
The Silver Mica types are mainly used for valve radio restoration and are expensive.
Please see link:

Silver Mica 1%

Regards,
Relayer
 
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There are film capacitors that are rated at 1%. But I, too, also question why your initial value can vary 100%, but you want a 1% tolerance????
 
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barry said:
...value can vary...
Click to expand...

Its a misunderstanding, I would accept any range 1-2uF so long as that value is 1% ideally it would be 1uF but not critical.
 

I’m curious what the end application is? Perhaps there is an alternative system level choice.


As an example linear’s TimerBlox parts are essentially digital and do 555 type timing stuff without relying on C Precision.
 
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There is an op-amp ckt that can act as a large fixed cap for signal levels - using a high precision cap (smaller) as a reference should allow you to synthesize what you are seeking ...
 
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Zak28 said:
Its a misunderstanding, I would accept any range 1-2uF so long as that value is 1% ideally it would be 1uF but not critical.
Click to expand...

Okay, so get a 1.5uF 20% capacitor. Measure it's value with a precision of 1%. Say it measures 1.62uF. You now have a 1.62uF capacitor with a tolerance 1%, which satisfies your requirement.

Bob
 
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bobTPH said:
...Measure it's value...
Click to expand...

Doesn't a cap tolerance mean its subject to change within tolerance? You make it seem it stays constant.
 

it depends on the dielectric and type of manufacture - most wound caps (like the old green caps) are quite stable over 10 -30 degC.

However disc ceramics are not, only C0G, or NPO have close temp tolerance - and you won't get those in 1uF, so a quality wound cap will suffice.

[ N.B. MLCC's are the same as disc ceramics ]
 
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Hi,

Okay, so get a 1.5uF 20% capacitor. Measure it's value with a precision of 1%. Say it measures 1.62uF. You now have a 1.62uF capacitor with a tolerance 1%, which satisfies your requirement.
Click to expand...

Usually tolerance includes:
* initial deviation
* drift by temperature (within specified temperature range)
* and other drifts

And "precision" means repeatability. --> Absolute value is given by "accuracy"

Klaus
 
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Besides temperature, humidity is a relevant drift factor. If you study manufacturers application notes, you'll find that among standard capacitor dielectrics, polypropylene gives best overall drift performance. 1% seems feasible.
 
FvM said:
Besides temperature, humidity is a relevant drift factor. If you study manufacturers application notes, you'll find that among standard capacitor dielectrics, polypropylene gives best overall drift performance. 1% seems feasible.
Click to expand...

@fvm - So the short answer is that the tolerance gives you and idea of its stability under various conditions e.g. Voltage , frequency , temp , humidity??? And you need to go to the datasheet to get and idea how it will perform in your particular application. Or is the manufacturer saying we really don't know what the value will be when we make it. But we guarantee it will be within this tolerance range.
 
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Hi,

Tolerance is some kind of overview ....
* you may have a 5% tolerated capacitor with high accuracy, but bad temperature drift
* but the capacitor may also have large fluctuations because of production... while it has low temperature drift.

Thus you need to read the datasheet carefully.

Klaus
 
The manufacturer is making the capacitors with a tolerance specification and doesn't guarantee anything beyond it. A brief check of distributor selection guides tells you that e.g. 1µF 1% polypropylene capacitors are listed but not stocked. You can expect that similar types with 5 or 10% tolerance have similar drift parameters. As discussed by bobTPH, they can be used for precision purposes after determining the exact capacitance.
 
Tolerance and stability are two different things. Here is an example. This is a 1uF C0G MLCC that is listed at 10% tolerance, but has a 30 ppm temperature coefficient and 0% / decade aging coefficient. In other words, once you determine it's exact value it will hold that well within 1% over a large range of temperatures and over time. A bit pricey though, I must admit.

https://www.mouser.com/ProductDetai...=sGAEpiMZZMs7ZEmUmaUL0/rmEoqVTxPK0eOXwgxfY6Y=

Bob
 
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