calling electronics gurus for help

[badger1666]

hope someone can help me out here, i know shit all about circuit design, but have no trouble building things.
here's my problem i have an ophir laser meter head , runs on +- 12v and powered up at stand still its off by +3mv .
the signal and common ground output can swing+ or - .
could i use a unity gain opamp circuit on its output to zero the output ??
if so could someone recomend a circuit i could use please

thanks

[dnar]

Are you really worried by the 3mV offset error?

You could use a unity gain amplifier and apply an adjustable offset to null the output, but the op-amp must be a low drift/low offset device int he first place.

I don't think 3mV is much of an offset error to warrant the effort, or perhaps I am wrong? What does +3mV represent?

[SrS]

1mV=1mW

What do you use to measure? most multimeters have a reletive/null function, this zero's the offset error.

[steve-o]

A resistor divider/ potentiometer could zero that 3mV outta there ..

[badger1666]

thanks
i supose really 3mv is nothing to worry about, was just being picky
@ steve-o nah a pots wont work, its two wire differential output
and the head wont work if you use a pot , i asked jerry and he said it was more complex than a pot
hence the opamp idea, and he has been helpfull enough, did not want to hassle him for a working idea
hence my post

[steve-o]

I'd have to see a schematic .. ok ..

[-bart-]

What you basically want to do is subtract a few mV.
So google summing amplifier. Apply an adjustable voltage to one input, apply your measurementsignal to the second.
You can make an adjustable voltage by dividing the supplyvoltage with a potentiometer and some additional resistors.
Wire a diode accros the pot if your suppy isn't regulated.

Be sure that the thermal head doesn't pick up residual IR, from you hand or drivers or psu.

[dnar]

A resistor divider/ potentiometer could zero that 3mV outta there ..

That would provide a scaling adjustment over the entire range (least were he needs it). An offset adjustment is required.

[steve-o]

Depends on where you put the pot.

[lasersbee]

I'm far from a Guru.... but....

I've done some tests on that "other" forum on the Surplus
OPHIR Heads... It turns out that not all the heads read the
same after letting the acclimate to the test area and then
powering it on for at least 15 minutes.

In the last year I've seen heads off by as much as 8mW when
acclimated to the test area....

There is a circuit board in the head with 2 gain controls and
one Zero adjust control ( i think I saw a pc of the inside posted
here a while back).

The 3mW offset can be eliminated by the Zero pot...
It is VERY important not to input any power to the sensor
and to NOT touch the Head with your fingers while doing
the zeroing..


Jerry