How to Use an HP 400D R.M.S. VTVM?
joshh...@fastmail.fm
one before, and I don’t have the manual for it.
The meter has a pair of jacks on the left front, with one labeled
INPUT and the one below it labeled G. There’s also a similar pair of
jacks on the right front, with the top one labeled OUTPUT and the
bottom one G again.
I’ve used multimeters and AC voltmeters many times before to measure
the voltage of my house wiring. I always stick the red lead in the
hot slot of a wall outlet and the black lead in the neutral slot to
get the reading. With this VTVM, however, if I stick the red INPUT
lead in the hot slot and the black G lead in the neutral slot, the
lead draws sparks from the outlet.
I figured there must be a short in the VTVM. But here’s the kicker:
If I stick just the red INPUT test lead in the hot slot of a wall
outlet, and leave the black lead disconnected, the meter reads 118
volts on the 300V scale. This appears to be a very accurate
reading.
So what’s the deal here with this meter? Is it designed to be
grounded with the G connector, and to use the INPUT to measure a
voltage by itself?
JP
wrote:
Stop doing that and go here, then to Bama to dl the manual
http://oak.cats.ohiou.edu/~postr/bapix/HP400D.htm
Phil Allison
"JP"
> Stop doing that and go here, then to Bama to dl the manual
> http://oak.cats.ohiou.edu/~postr/bapix/HP400D.htm
** No manual there.
Just a story about one being restored and checked out.
... Phil
Phil Allison
<joshh...@fastmail.fm
I picked up an HP 400D R.M.S. VTVM at an estate sale. I’ve never used
one before, and I don’t have the manual for it.
The meter has a pair of jacks on the left front, with one labeled
INPUT and the one below it labeled G. There’s also a similar pair of
jacks on the right front, with the top one labeled OUTPUT and the
bottom one G again.
I’ve used multimeters and AC voltmeters many times before to measure
the voltage of my house wiring. I always stick the red lead in the
hot slot of a wall outlet and the black lead in the neutral slot to
get the reading. With this VTVM, however, if I stick the red INPUT
lead in the hot slot and the black G lead in the neutral slot, the
lead draws sparks from the outlet.
** This meter is not meant for nor safe around AC mains wiring.
So what’s the deal here with this meter? Is it designed to be
grounded with the G connector, and to use the INPUT to measure a
voltage by itself?
** That HP VTVM is a special bench test instrument - not a general purpose
AC voltmeter.
The latter have plastic cases, run on batteries and can be connected to a
voltage source any way round you like.
..... Phil
Mike Coatham
The meter may be faulty - download the manual (inc. circuit diagram) from
here :
http://bama.edebris.com/manuals/hp/400d/
If you don't know how to check & repair the meter then find someone who
can. If it was working properly, you'd be able to measure AC voltages from
.1 millivolts to 300 volts.
Phil Allison
"Mike Coatham"
>> I picked up an HP 400D R.M.S. VTVM at an estate sale. I’ve never used
>> one before, and I don’t have the manual for it.
>>
>> The meter has a pair of jacks on the left front, with one labeled
>> INPUT and the one below it labeled G. There’s also a similar pair of
>> jacks on the right front, with the top one labeled OUTPUT and the
>> bottom one G again.
>>
>> I’ve used multimeters and AC voltmeters many times before to measure
>> the voltage of my house wiring. I always stick the red lead in the
>> hot slot of a wall outlet and the black lead in the neutral slot to
>> get the reading. With this VTVM, however, if I stick the red INPUT
>> lead in the hot slot and the black G lead in the neutral slot, the
>> lead draws sparks from the outlet.
>>
>> I figured there must be a short in the VTVM. But here’s the kicker:
>> If I stick just the red INPUT test lead in the hot slot of a wall
>> outlet, and leave the black lead disconnected, the meter reads 118
>> volts on the 300V scale. This appears to be a very accurate
>> reading.
>>
>> So what’s the deal here with this meter? Is it designed to be
>> grounded with the G connector, and to use the INPUT to measure a
>> voltage by itself?
>
> The meter may be faulty - download the manual (inc. circuit diagram) from
> here :
>
> http://bama.edebris.com/manuals/hp/400d/
** The manual makes it very clear this unit has the input ground connected
to the chassis and AC plug.
So there is no fault.
There is a warning on page 15 of the PFD about de-earthing the unit making
it hazardous to the user.
..... Phil
sucke...@gmx.us
always be ground and neutral should always be neutral. Plus, ground
and neutral should be isolated in the unit itself. There should either
be zero or 220 volts between ANY two hot side of plug, since half the
outlets are connected to one hot wire and half the other.
Phil Allison
<sucke...@gmx.us
>
> You need to check your house wiring, for one thing. Ground should
> always be ground and neutral should always be neutral.
** So what voltage is OK to see on the neutral ?
> Plus, ground
> and neutral should be isolated in the unit itself.
** Nothing suggests otherwise - does it ?
> There should either
> be zero or 220 volts between ANY two hot side of plug, since half the
> outlets are connected to one hot wire and half the other.
** You suggesting the OP use his HP400D to check that ?
With its input and CASE connected to AC supply ground ??
Insane.
...... Phil
BretLudwig
However Phil does not need to be cuntish about it.
As to his question:
>>"** So what voltage is OK to see on the neutral ?"<<
the answer is: it varies, but "several volts is not uncommon nor
acceptable, referenced to earth ground" is a common and accurate one.
Neutral or "earthy" in Britspeak is tied to ground or "earth" at ONE and
ONLY ONE place.
Using 220V balanced power in the US, or three phase power where
available, solves many problems and is the preferred power source if the
receiving equipment is properly designed or modified. Bi-phase power IS a
lot easier to use than quadrature (two phase, now obsolete in the US) or
three phase however. The latter require a lot of diodes and caps... They
do perform better though, though it's a moot point as in the US three
phase power is unobtanium in houses (unless you buy a rotary converter or
a gen set, q.f. the choo choo chiller so chic in alt-power circles).
--
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