B&K 290 multimeter alignment?

J

JOHN D

Guest
I got this B&K 290 multimeter at a garage sale. It needs a little
calibration. Most of the adjustment pots are marked but its not intirely
clear how they are used. One pot mounted on the range switch is not labled.
Anyone have the calibration instructions for it?
Remove 1 to reply.
 
JOHN D wrote:
I got this B&K 290 multimeter at a garage sale. It needs a little
calibration. Most of the adjustment pots are marked but its not intirely
clear how they are used. One pot mounted on the range switch is not labled.
Anyone have the calibration instructions for it?
Remove 1 to reply.


I have found that each pot is close to the function it controls
Click to expand...
(looking at the top side of range switch).
One can always remember a setting, and move the pot 1/4 turn to see
if the reading changes; then move it back.
So if you wish to calibrate the voltage scale, apply a voltage known
to a better accuracy than the meter, then tweak the selected pot as
mentioned and go to the next one; when found you can adjust appropiately.
The voltage calibration should be done first (above range switch); it
seems to control current and resistance. The other control (below range
switch) can usually be left alone (capacitance).
Some meters have as many as 6 pots; upper left usually voltage, lower
left usually capacitance; lower right (near thermocouple input) isfor
temperature); have not fiddled with the others.
 
"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:vE90e.1855$gI5.406@newsread1.news.pas.earthlink.net...
JOHN D wrote:
I got this B&K 290 multimeter at a garage sale. It needs a little
calibration. Most of the adjustment pots are marked but its not intirely
clear how they are used. One pot mounted on the range switch is not
labled.
Anyone have the calibration instructions for it?
Remove 1 to reply.


I have found that each pot is close to the function it controls
(looking at the top side of range switch).
One can always remember a setting, and move the pot 1/4 turn to see
if the reading changes; then move it back.
So if you wish to calibrate the voltage scale, apply a voltage known
to a better accuracy than the meter, then tweak the selected pot as
mentioned and go to the next one; when found you can adjust appropiately.
The voltage calibration should be done first (above range switch); it
seems to control current and resistance. The other control (below range
switch) can usually be left alone (capacitance).
Some meters have as many as 6 pots; upper left usually voltage, lower
left usually capacitance; lower right (near thermocouple input) isfor
temperature); have not fiddled with the others.

Thanks for the reply.
There's no capacitance or temperature on this thing. It's a 115 v powered
Click to expand...
solid state (FET I think)VOM
All but one pot is labled.,
(+DC Cal), (-DC Cal), & (AC Cal). These are probable obvious
(Bias Adj), (Bal Adj) I can only guess at these
(Hi ohm Cal) not sure about this one. There's a Lo Pwr & Hi Pwr resistance
function. it seems to affect zero.
AC & DC voltage reads about 9% low
A large zero adjustment is needed when switching between Lo Pwr & Hi Pwr but
the reading is close. The zero pot is near the end of its rotation.
John
 
"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:Igv0e.2610$gI5.2035@newsread1.news.pas.earthlink.net...
JOHN D wrote:
"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:vE90e.1855$gI5.406@newsread1.news.pas.earthlink.net...


Wierd to have two different power levels for resistance...
Click to expand...
I think it has to do with providing enough current to turn on solid state
devices. I don't remember where I learned this but supposedly some meters
would falsely show a diode as open cus there wasn't enough current in the
resistance circuit to turn it on..
 
JOHN D wrote:

"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:Igv0e.2610$gI5.2035@newsread1.news.pas.earthlink.net...

JOHN D wrote:

"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:vE90e.1855$gI5.406@newsread1.news.pas.earthlink.net...



Wierd to have two different power levels for resistance...


I think it has to do with providing enough current to turn on solid state
devices. I don't remember where I learned this but supposedly some meters
would falsely show a diode as open cus there wasn't enough current in the
resistance circuit to turn it on..


No, it is not the current; it is the voltage compliance.
Click to expand...
There must be sufficent voltage to drive the desired current, for the
diode to conduct in the forward direction.
Note only germanium, silicon and schottky diodes work; LEDs do not.
Hand-held DVMs seem to use about 1mA (some more, some less).
However, one can determine diode types with 10uA or with 100mA.
The 1mA is chosen, so that the voltage drop that is measured, is
recognizable by savvy electronic technicians.
A silicon diode conducts rather well at 1uA, but would have a voltage
drop roughly 200mV less than that expected in "normal" circuits; if you
read 430mV, you might think you had a germanium or a schottky diode
(those would read much lower).
 
JOHN D wrote:
"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:vE90e.1855$gI5.406@newsread1.news.pas.earthlink.net...

JOHN D wrote:

I got this B&K 290 multimeter at a garage sale. It needs a little
calibration. Most of the adjustment pots are marked but its not intirely
clear how they are used. One pot mounted on the range switch is not

labled.

Anyone have the calibration instructions for it?
Remove 1 to reply.



I have found that each pot is close to the function it controls
(looking at the top side of range switch).
One can always remember a setting, and move the pot 1/4 turn to see
if the reading changes; then move it back.
So if you wish to calibrate the voltage scale, apply a voltage known
to a better accuracy than the meter, then tweak the selected pot as
mentioned and go to the next one; when found you can adjust appropiately.
The voltage calibration should be done first (above range switch); it
seems to control current and resistance. The other control (below range
switch) can usually be left alone (capacitance).
Some meters have as many as 6 pots; upper left usually voltage, lower
left usually capacitance; lower right (near thermocouple input) isfor
temperature); have not fiddled with the others.

Thanks for the reply.

There's no capacitance or temperature on this thing. It's a 115 v powered
solid state (FET I think)VOM
All but one pot is labled.,
(+DC Cal), (-DC Cal), & (AC Cal). These are probable obvious
(Bias Adj), (Bal Adj) I can only guess at these
(Hi ohm Cal) not sure about this one. There's a Lo Pwr & Hi Pwr resistance
function. it seems to affect zero.
AC & DC voltage reads about 9% low
A large zero adjustment is needed when switching between Lo Pwr & Hi Pwr but
the reading is close. The zero pot is near the end of its rotation.
John


Sorry, i was referring to hand-held DVMs.
Click to expand...
But it seems that you know what most of the pots are for.
Anyone that designs a VOM that needs seperate + and - DC cal is
profoundly stupid. And the AC cal could easily be "automatic" by using
the DC measurement system / cal.
Wierd to have two different power levels for resistance...
 
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