Re: Opamp noise [ solder it all together? ]

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
.

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