Fluke 800A bench multimeter: normal behaviour or defect?

[[email protected]]

G'day,

I've recently acquired an old bench multimeter, a Fluke 800A.

On the most sensitive AC-range (200mV AC) it seems to 'overflow'
(displaying 1999mV) when leads are attached. Is this normal behaviour
for this equipment? When shorting the leads, it displays correctly. On
the 2V AC range, it displays about 0.3VAC...

Is this because of RF interference in the air (but why don't my other
multimeters have it so badly?) or is it in need of repair?

If it's repair that's needed, any idea where to start looking? Or, does
anyone have a schematic or service manual available for this Fluke
800A?

Sincerely,

Peter,
The Netherlands.

 

[Sam Goldwasser]

G'day,

I've recently acquired an old bench multimeter, a Fluke 800A.

On the most sensitive AC-range (200mV AC) it seems to 'overflow'
(displaying 1999mV) when leads are attached. Is this normal behaviour
for this equipment? When shorting the leads, it displays correctly. On
the 2V AC range, it displays about 0.3VAC...

Is this because of RF interference in the air (but why don't my other
multimeters have it so badly?) or is it in need of repair?

If you mean just hanging not connected to anything, it's probably
normal. If it zeros when they are shorted, then it's likely working.

Measure something to confirm.

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[Jerry G.]

With the leads hanging in the air, being unterminated, it is normal
that the instrument will pick up some voltage, or AC radiation from the
surrounding environment, such as from the wiring in the walls, and etc.
The 200 mv scale is very sensitive.

The proper way to test this is if the leads are shorted, and the meter
zeros, indicates that the meter is able to be referenced.

The second part of the basic test is to have a known proper calibrated
AC voltage source that is in the 200 mv range, to see if the meter is
accurate.

Jerry G.
======

 

[[email protected]]

Thanks, Sam and Jerry.

Will give it a try with a (more or less accurate ) mv AC-source.
All the other ranges work fine, as far as I can tell, only the mV AC
range overflowed. Strange that none of my other multimeters show this
behaviour (or at least much less; about 30-40mV on the 200mV range).

All that's left to do is find some good testleads for this Fluke, and
it'll be ready for everyday use.

Grtz,

Peter PE1VCC

 

[Steven Swift]

The 8000A was designed before anyone cared about RFI to instruments. It
has a very sensitive front end and an A/D conversion scheme that is
susceptible to rfi.

The cool thing about the 8000A is that is uses calibrated current sources
to measure ohms. It has 200mV and 2V basic ranges and the currents are
adjusted to give the right full scale range. For example, the 2k range
puts out 1ma. Fluke later featured this range and called it diode test on
the newer instruments. You can push in both the current buttons and the
ohms buttons to measure your current.

Makes a nice little current source for matching diodes, etc.