Millivolt power supply

[Joe]

Hello; I am in need of a 0-50 mv source for testing some meters for my
boss.All of the meters have either current or voltage scales but FS
readings are all within the 0-50mv range. I thought of using a
standard power supply along with a voltage divider but the resistor
sizes and tolerances just don't give a good variable output without
alot of readjustments. Thanks

 

[Tweetldee]

Why not use the voltage divider on the input of an opamp set up as a unity
gain noninverting buffer amp. The high input impedance of a noninverting
amp won't load the divider, and if necessary, can easily be nulled. Be sure
to select an opamp that can handle the current that the meters need.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Time is what keeps everything from happening all at once.
"Joe" <etrak@surfbest.net> wrote in message
news:6d1e70fc.0309191000.3cef5a05@posting.google.com...

Hello; I am in need of a 0-50 mv source for testing some meters for my
boss.All of the meters have either current or voltage scales but FS
readings are all within the 0-50mv range. I thought of using a
standard power supply along with a voltage divider but the resistor
sizes and tolerances just don't give a good variable output without
alot of readjustments. Thanks

 

[Sam Goldwasser]

etrak@surfbest.net (Joe) writes:

Hello; I am in need of a 0-50 mv source for testing some meters for my
boss.All of the meters have either current or voltage scales but FS
readings are all within the 0-50mv range. I thought of using a
standard power supply along with a voltage divider but the resistor
sizes and tolerances just don't give a good variable output without
alot of readjustments. Thanks

What type of meters? Moving coil meters are generally rated in full scale
current, regardless of what the scale itself says unless the current limiting
resistors are bulit in.

A variable power supply with a voltage divider and pot is the simplest.

As someone else suggested, an op-amp can be added to provide a low impedance
voltage output but this really isn't needed.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the Feedback Form at repairfaq.org. Thanks.

 

[Jim Yanik]

etrak@surfbest.net (Joe) wrote in
news:6d1e70fc.0309191000.3cef5a05@posting.google.com:

Hello; I am in need of a 0-50 mv source for testing some meters for my
boss.All of the meters have either current or voltage scales but FS
readings are all within the 0-50mv range. I thought of using a
standard power supply along with a voltage divider but the resistor
sizes and tolerances just don't give a good variable output without
alot of readjustments. Thanks

Keithley makes low voltage sources,try Ebay for some used ones,or look for
meter calibrators.

IIRC,Keithley has a website,Google should find it.

--
Jim Yanik,NRA member
jyanik@kua.net

 

[mike]

Joe wrote:

Hello; I am in need of a 0-50 mv source for testing some meters for my
boss.All of the meters have either current or voltage scales but FS
readings are all within the 0-50mv range. I thought of using a
standard power supply along with a voltage divider but the resistor
sizes and tolerances just don't give a good variable output without
alot of readjustments. Thanks

You're almost always better off testing analog meters with current,
cause that's what they measure.
If you need to know the voltage, measure it across the meter with a dvm.
Lots easier than trying to build a calibrated voltage source. All you
need is a sloppy voltage source and an approximate resistor value and
a crummy (or better) dvm. If you need to know the current accurately,
you'll need a calibrated resistor or a dvm that measures current in
series with the resistor.

mike

--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
4in/400Wout ham linear amp.
Honda CB-125S
400cc Dirt Bike 2003 miles $550
Police Scanner, Color LCD overhead projector
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Jim Yanik]

mike <spamme0@juno.com> wrote in news:3F6D1993.5090802@juno.com:

Joe wrote:
Hello; I am in need of a 0-50 mv source for testing some meters for my
boss.All of the meters have either current or voltage scales but FS
readings are all within the 0-50mv range. I thought of using a
standard power supply along with a voltage divider but the resistor
sizes and tolerances just don't give a good variable output without
alot of readjustments. Thanks

You're almost always better off testing analog meters with current,
cause that's what they measure.
If you need to know the voltage, measure it across the meter with a dvm.
Lots easier than trying to build a calibrated voltage source. All you
need is a sloppy voltage source and an approximate resistor value and
a crummy (or better) dvm. If you need to know the current accurately,
you'll need a calibrated resistor or a dvm that measures current in
series with the resistor.

mike

One other accurate voltage source I forgot about would be a Fluke
differential voltmeter,like the 893 or similar ones. They measure voltage
by bucking their internal calibrated voltage supply against the input V,and
nulling a sensitive meter.You could get one cheap on Ebay,or from a used
Test Equipment company.

Hook it up to your device under test(DUT),and adjust the Fluke for a full-
scale reading on the DUT,and read the voltage out off the dials.



--
Jim Yanik,NRA member
jyanik@kua.net