Poly Capacitors

[Vortxrex]

Rounding up parts for my HH & Surf PI projects, but having a problem finding polyester Capacitors .001 uf & .022 uf. 5% tolerance

I found mylar caps at Jameco 10% tolerance. I am thinking if I buy a bunch of the mylar caps & check the values, some will be within 5%... Are there other reasons not to use mylar in place of poly?

Where is everyone getting their capacitors?

all help appreciated

Dave Frank

[Vortxrex]

OK, I figured it out

-Dave Frank

[mikebg]

I found mylar caps at Jameco 10% tolerance. I am thinking if I buy a bunch of the mylar caps & check the values, some will be within 5%... Are there other reasons not to use mylar in place of poly?
Dave Frank

Vortxrex, this is not true.
Tolerance of a device is the permissible deviation from nominal specified value. It means maximal variation of
electrical parameter that can be tolerated at aging of device without impairing its operation.
The term "tolerance" is close to term "stability" of parameter at aging, temperature and humidity change. Tolerance not depends on precise measurement of parameter at sorting. If you can measure the value of a device with a precise instrument, that not means you increase its tolerance. Tolerance is limited by ability of producer to design and make stabile devices.
Only designer team of producer and used materials and technology can improve the tolerance.
REMEMBER: You can not measure the tolerance. You can measure only deviation from nominal value. The manufacturer guarantees that at aging this deviation will be less than noted tolerance.

[pebe]

Vortxrex, this is not true.
Tolerance ....... means maximal variation of
electrical parameter that can be tolerated at aging of device without impairing its operation.
The term "tolerance" is close to term "stability" of parameter at aging, temperature and humidity change. Tolerance not depends on precise measurement of parameter at sorting. If you can measure the value of a device with a precise instrument, that not means you increase its tolerance. Tolerance is limited by ability of producer to design and make stabile devices............

Many years ago I worked for a large component manufacturer whose range included resistors, potentiometers and electrolytic capacitors. Your definition of 'tolerance' was certainly not the case then. The manufactured value of each item had to fall within the tolerance band as the item was tested prior to leaving the factory.

Long term ageing did not enter the equation. That was dealt with in the data sheet for the particular item, as far as was possible. But who would vouch for the stabilty of a composition resistor after 5 years in service? Or the capacity of an elecrolytic after running with a very low DC voltage on it? Component failure was the reason for flourishing electronics repair businesses. Now the reliabilty of carbon film and metal film resistors make for equipment which is so reliable that it becomes uneconomical to repair.

[Qiaozhi]

Many years ago I worked for a large component manufacturer whose range included resistors, potentiometers and electrolytic capacitors. Your definition of 'tolerance' was certainly not the case then. The manufactured value of each item had to fall within the tolerance band as the item was tested prior to leaving the factory.

Long term ageing did not enter the equation. That was dealt with in the data sheet for the particular item, as far as was possible. But who would vouch for the stabilty of a composition resistor after 5 years in service? Or the capacity of an elecrolytic after running with a very low DC voltage on it? Component failure was the reason for flourishing electronics repair businesses. Now the reliabilty of carbon film and metal film resistors make for equipment which is so reliable that it becomes uneconomical to repair.

I was going to reply to that post with a similar answer, but something distracted me and ..... where was I?
Totally agree with your response. The tolerance value has nothing to do with aging.

[mikebg]

I was going to reply to that post with a similar answer, but something distracted me and ..... where was I?
Totally agree with your response. The tolerance value has nothing to do with aging.

I will give examples of tolerance in several areas of electronics:

1. Measuring instruments.
You can disassemble your DMM (digital muultimeter) to see what tolerance is written on its R and C components. Since its designer has provided such a small tolerance, your unit will measure precisely after more than 5 years.

2. Medical electronics.
My job is inspection and maintenance of medical electronic equipment. Over many years I measure the parameters of medical devices manufactured by various companies. Some instruments are in daily use for over 30 years. Their parameters should be checked periodically because deviation from them can be put to misdiagnosis or a patient to receive disability improper therapy. In the new models the self-inspection is build and automated. The notion of irregularity block apparatus and appears an alert. The components used have very little tolerance. The irregularities in such devices are usually due to semiconductor components.

3. Military electronics.
I have hobby colleagues, professionally involved in military electronics. They argue that in the past 40 years had no a case of damage due to the change resistance of a resistor or capacitance of a capacitor. Electrolytic capacitors in the military equipment are tantalum because they have less tolerance.

4. Computers. Service experts say that damages in PC are not caused by changing the values of R and C components at aging. These components are damaged due to malfunction of semiconductor devices. In the power supply of my old computer has 5 electrolytic capacitors connected in parallel, instead of using a capacitor. They are heated by ongoing strong current pulses. At first glance it appears that the reliability of this design is reduced due to the increased number of componens. The price is increased. However parallel connection connection reduces tolerance of ESR parameter

5. Metal detectors for prófesionals.
See the tolerances of the used R and C components in a truly professional model. Why in the attached diagram of an amplifier are used very strange values of resistors? Why are such small tolerances? We can use in the circuit capacitors with a tolerance 10% instead of 5% because they are cheaper. We may use and cheaper resistors with tolerance 2% and even 5% instead of shown by designer 1%. If we make such an exchange of components, we can adjust with R5 and R10 the same parameters. However, the metal detector ceases to be a professional model. We can not guarantee that it will not increase noise and will not alter the phase characteristics after a few years (or after cyclic change in humidity and temperature).

[Vortxrex]

mikebg wrote: "Why are such small tolerances? We can use in the circuit capacitors with a tolerance 10% instead of 5% because they are cheaper. We may use and cheaper resistors with tolerance 2% and even 5% instead of shown by designer 1%. If we make such an exchange of components, we can adjust with R5 and R10 the same parameters. However, the metal detector ceases to be a professional model"


I see a 1% resistor connected in series w/ a potentiometer R5.. That makes no sense to me, same story with R10 & R11.

Digikey will to sell me the 5% .001uf Polyester/Mylar cap, but only if I buy 1000 of them. Jameco has a 10% .001uf and I can buy them in lots of 10, that's what I am going to do & I will use the ones that measure closest to .001uf..... Dave Frank

[Qiaozhi]

I will give examples of tolerance in several areas of electronics:

1. Measuring instruments.
You can disassemble your DMM (digital muultimeter) to see what tolerance is written on its R and C components. Since its designer has provided such a small tolerance, your unit will measure precisely after more than 5 years.

2. Medical electronics.
My job is inspection and maintenance of medical electronic equipment. Over many years I measure the parameters of medical devices manufactured by various companies. Some instruments are in daily use for over 30 years. Their parameters should be checked periodically because deviation from them can be put to misdiagnosis or a patient to receive disability improper therapy. In the new models the self-inspection is build and automated. The notion of irregularity block apparatus and appears an alert. The components used have very little tolerance. The irregularities in such devices are usually due to semiconductor components.

3. Military electronics.
I have hobby colleagues, professionally involved in military electronics. They argue that in the past 40 years had no a case of damage due to the change resistance of a resistor or capacitance of a capacitor. Electrolytic capacitors in the military equipment are tantalum because they have less tolerance.

4. Computers. Service experts say that damages in PC are not caused by changing the values of R and C components at aging. These components are damaged due to malfunction of semiconductor devices. In the power supply of my old computer has 5 electrolytic capacitors connected in parallel, instead of using a capacitor. They are heated by ongoing strong current pulses. At first glance it appears that the reliability of this design is reduced due to the increased number of componens. The price is increased. However parallel connection connection reduces tolerance of ESR parameter

5. Metal detectors for prófesionals.
See the tolerances of the used R and C components in a truly professional model. Why in the attached diagram of an amplifier are used very strange values of resistors? Why are such small tolerances? We can use in the circuit capacitors with a tolerance 10% instead of 5% because they are cheaper. We may use and cheaper resistors with tolerance 2% and even 5% instead of shown by designer 1%. If we make such an exchange of components, we can adjust with R5 and R10 the same parameters. However, the metal detector ceases to be a professional model. We can not guarantee that it will not increase noise and will not alter the phase characteristics after a few years (or after cyclic change in humidity and temperature).

There is no argument that the parameters of electronic components will change with age. This is common knowledge.

However, the tolerance value of a component will not tell you anything about how this value will change over time. It is simply an indication that the component in question is guaranteed to have a value which lies between a specified range at the time of manufacture. For example, a 1k 5% resistor is unlikely to have an exact value of 1k ohms. The value will be somewhere between 950 ohms and 1050 ohms. The distribution of this value is usually Gaussian, but different distributions are possible, depending on the situation. This is why a Monte Carlo SPICE simulation is so useful in determining that correct tolerancing has been used in the design process.