Re: Opamp noise [ solder it all together? ]

comp.arch.embedded.piclist wrote:
On Nov 28, 2:29 pm, Glenn Møller-Holst <nom...@xxxxx> wrote:
comp.arch.embedded.piclist wrote:

...

Heres the link.
http://www.williams-eng.com/circuit/circuit.html
Thanks
Hi Jim

My remedy:

(1) I think you have to solder your prototype circuit together - and
with as few solder joints as possible.

You can not use a prototype circuit, unless both wires and board springs
have non-corroding metal contacts (gold...).

I have measured voltage "steps", in a cheap switch, while conducting
current, because of small corrosion island (I assume). The switch is
used for voltage division resistor ladder, in a home-made active analog
voltage/current meter. It has a gain switch to change full scale between
10, 20 and 50mV.

If either your wires - or springs have contaminations og corrosion
island, you have got noise.

Airborne smog/pollution will corrode, what can be corroded (with "help"
from humidity and airborne saltcrystal). It can induce voltage, when
united with the difference in springs and wire metal (alloys):http://en.wikipedia.org/wiki/Galvanic_cell
(Might also be relevant:http://en.wikipedia.org/wiki/Thermoelectric_effect):
Kelvin (4-wire) resistance measurement:http://www.ohmite.com/cgi-bin/showpage.cgi?product=10_series
Quote: "...The four terminal design also results in a lower temperature
coefficient of resistance and lower self-heating drift which may be
experienced on two-terminal resistors...Thermal EMF: Less than ±2uV/°C..."

(I lowered the contact noise and contact resistance from 10 mOhm to 9
mOhm by greasing the switch contact plates and spring with super lube -
silicone oil + very small teflon balls). I have measured the contact
resistance on a separatly greased switch after 1, 2 and 3 years - and it
still has the low 9 mOhm.

I know that power switches must not be greased, because the sparks burn
some of the grease, transforming the grease to other chemicals that may
be conducting electricity much better.

(2) Make sure your variable resistors has been gold plated - or maybe
use a little to big resistor in parallel with a "big" variable resistor.
Then the variable resistor will have the least noise addition (I think).

-

Some years ago I got a fine looking TV, that worked very erratically.
Just by pushing the frame a little (or not at all), the red, green or
blue color vanished, it shutdown or more obscure problem (dis-,re-)appeared.

The problem was that all the ICs was in transparent plastic IC-sockets.
The sockets internal pin springs could be seen, and was black of
corrosion, and that was the cause of the erratic behavior. Very small
black flakes could be seen through the plastic.

Nowadays nearly all IC-sockets are non-transparent black - why? ;-)

-

INA126:http://courses.cs.tamu.edu/rgutier/ceg499_s02/sbos062.pdf

regards,

Glenn

What type of caps are the best to use for this. Ceramic, mylar, mica,
tantalum ...?


For bypassing and suppressing RF? Ceramic SMT caps in 0603 size. 0805 size is mostly ok, too. 0.1uF directly from each supply pin to the ground plane. Directly, not 1/2" further down the road. For input signal filters you'll have to coarsely calculate the roll-off. Also, I wouldn't push it too low since ceramic caps have somewhat of a memory effect and act as a microphone to some extent. Use X7R ceramic on the supply and smaller C0G caps on the signals (unless you need large values).

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
.

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