Alternate for CA3160 mosfet op-amp?
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Gathering parts for my next experiment (Tracy Allan's pH
transmitter). The CA3160 isn't available locally. I can't seem to
find a cross-reference or even a datasheet for it online.
Active components has three mosfet op-amps in thier catalog but not
stocked in store. Meaning I have to buy 50 or so at once.
Any equivilent parts I can go looking for at other stores that you
folks know of?
Oh and one other newb question. In the drawing there are two
different symbols for capacitors. One is two parallel lines and the
other is the same but the ends of one line are turned down. What is
the signifigance of that?
transmitter). The CA3160 isn't available locally. I can't seem to
find a cross-reference or even a datasheet for it online.
Active components has three mosfet op-amps in thier catalog but not
stocked in store. Meaning I have to buy 50 or so at once.
Any equivilent parts I can go looking for at other stores that you
folks know of?
Oh and one other newb question. In the drawing there are two
different symbols for capacitors. One is two parallel lines and the
other is the same but the ends of one line are turned down. What is
the signifigance of that?
Comments
older stuff. Two straight lines is a non-polarized cap.
The curvy line usually denotes the negative side of a
polarity-sensitive cap.
Jack
ghidera2000 wrote:
>
> Gathering parts for my next experiment (Tracy Allan's pH
> transmitter). The CA3160 isn't available locally. I can't seem to
> find a cross-reference or even a datasheet for it online.
>
> Active components has three mosfet op-amps in thier catalog but not
> stocked in store. Meaning I have to buy 50 or so at once.
>
> Any equivilent parts I can go looking for at other stores that you
> folks know of?
>
> Oh and one other newb question. In the drawing there are two
> different symbols for capacitors. One is two parallel lines and the
> other is the same but the ends of one line are turned down. What is
> the signifigance of that?
>transmitter). The CA3160 isn't available locally. I can't seem to
>find a cross-reference or even a datasheet for it online.
I still have a pile of those old RCA op amps lying around, but they
are really dated. Don't go out and purchase any! I never use them
for anything any more, so let me know if you want one in trade for a
couple of stamps.
The important parameter for a pH amplifier is low input bias current,
so a CMOS input is essential. There are a lot of op amps today that
would work.
The National LMC6081 would be a good substitution. You can get free
samples from National, or purchase them from Digikey etc.
The LMC6081 has a typical input bias current of 10 femtoamperes.
(femto=ten to the minus 15th power). pH electrodes are like a small
battery outputting a voltage on the order of +/-1 volt, but in series
with a very large and unstable "source resistance", say 10 to 100
megaohms. What you want to get at is the voltage. The op amp bias
current flowing through that resistance causes an error. 10 femto
amperes through 100 megaohms causes negligible error, less than a
microvolt. But if you were to use a general purpose op amp with, say
1 nanoamp bias current (10E-9), then the error could be 0.1 volt,
which is not negligible at all.
-- best regards
Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
mailto:tracy@e...
>
>Active components has three mosfet op-amps in thier catalog but not
>stocked in store. Meaning I have to buy 50 or so at once.
>
>Any equivilent parts I can go looking for at other stores that you
>folks know of?
>
>Oh and one other newb question. In the drawing there are two
>different symbols for capacitors. One is two parallel lines and the
>other is the same but the ends of one line are turned down. What is
>the signifigance of that?
>couple of stamps
not Stamps, just stamps, you know what I mean?!
> >in trade for a
> >couple of stamps
>
> not Stamps, just stamps, you know what I mean?!
Hehe, two Javelin stamps for the OpAmp what? [noparse]:D[/noparse]
Thanks for the offer! I'll keep attempting to find something locally
for now. If I build it and later have to repair, I would rather have
something I can pop down to the corner and purchase a replacement for.
Besides, you KNOW the day after you mailed it off, something would
break and you'd need one - and it'd be something vital like a sump
pump controller that kept your basement from flooding with sewage (At
least, thats the way it always seems to happen for me).
buttload of the CA3160's in Victoria - receiving four of them
tomorrow. Only $2 each so I got two extras. [noparse]:D[/noparse]