Re: [volt-nuts] Fluke differential meters
Hi Robert
Your comments reminded me that some years ago I bought a Fluke differential
voltmeter and a hernia inducing struggle through other equipment to reach
it down from a shelf just confirmed it's an 893A.
I must admit I was more interested in the case when I bought it, sacrilege
I know but at least it looked too nice to take apart so did remain intact,
and I'm much more inclined now to leave it that way:-)
Component markings suggest this one dates from around 1984 and it uses the
same style blue plastic switch wafers in the Kelvin-Varley divider that
later became notorious for failing on the Redifon 551 HF receiver.
There are, or were, some references on line to repairing the switches in
the 551 and I have seen the wafers offered for sale from time to time, I seem
to recall they were also used in one version of the RS components
"make-a-switch" kit.
As far as I can tell from the manual though and unless I'm missing
something, which isn't entirely unkown:-), the voltage reference consists of a
pair of zener diodes rather than a Weston cell.
Either way, I've just discovered one of the switches is jammed, the wafers
look ok and I don't recall it being jammed when I bought it so not sure why
yet, but there goes what I already had planned for today:-)
Regards
Nigel
GM8PZR
In a message dated 07/08/2013 07:37:44 GMT Daylight Time,
robert8rpi@yahoo.co.uk writes:
Hi Joe,
The 893 is worth having as a working instrument. The older ones are
collectibles (possibly) or a source of parts. The Voltage reference is a Weston
cell which will be well past it's expected life. In particular these meters
have a Kelvin Varley voltage divider. This can be used without the meter
section working, possibly recased. The plastic switch dials/drums do tend to
crack or warp due to srinkage of the plastic though. If theK-V dividers
switches are worn out, they are still a good source for precision matched
resistors. Perhaps not spot on value but all the resistors in a decade will be
very close in value. These can be used for voltage dividers and Hamon
resistor units (google Hamon resistor and see
http://conradhoffman.com/HamonResistor.html ). They may not look much but are high performance. There are
other precision resitors in these units Take care when removing them, don't
apply any force or stress to the resistor body as this can affect
their performance.
Robert G8RPI.
From: Joseph Gray jgray@zianet.com
To: Discussion of precise voltage measurement volt-nuts@febo.com
Sent: Wednesday, 7 August 2013, 6:00
Subject: [volt-nuts] Fluke differential meters
The local surplus guy has at least three different differential meters that
have been collecting dust for decades. I have borrowed two of them (so
far).
The first one is a Fluke 893A and is solid state. Although it appears to
work, it fails the very first of the performance tests. Now that I have a
full manual, I'm going to look at this a bit closer.
The second one is a Fluke 803B (I think. There is no label on it). It has
tubes. I am slowly bringing it up on a variac before messing with it. I
plan to open it up later and take a good look.
I'm not sure what the third model is, but it looks like it may be an even
older Fluke. It is on a high shelf and I haven't gone over there to lift it
down yet. I'll probably do that later this week.
At the moment, I'm just playing around with this gear and learning a few
things. In the long run, are these things worth having?
Joe Gray
W5JG
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Hi Nigel,
I just re-read my post and I wan't very clear. I was trying to say that the 803B has a Weston cell reference. Jammed switches are often caused by the readout drums shrinking and seizing on the shaft :-( . Watch out for the switch wafers, at least on the higher accuracy units they were impregnated with silicone oil to reduce leakage. Standard waferes may not be up to specification.
Regards,
robert G8RPI.
From: "GandalfG8@aol.com" GandalfG8@aol.com
To: volt-nuts@febo.com
Sent: Wednesday, 7 August 2013, 11:10
Subject: Re: [volt-nuts] Fluke differential meters
Hi Robert
Your comments reminded me that some years ago I bought a Fluke differential
voltmeter and a hernia inducing struggle through other equipment to reach
it down from a shelf just confirmed it's an 893A.
I must admit I was more interested in the case when I bought it, sacrilege
I know but at least it looked too nice to take apart so did remain intact,
and I'm much more inclined now to leave it that way:-)
Component markings suggest this one dates from around 1984 and it uses the
same style blue plastic switch wafers in the Kelvin-Varley divider that
later became notorious for failing on the Redifon 551 HF receiver.
There are, or were, some references on line to repairing the switches in
the 551 and I have seen the wafers offered for sale from time to time, I seem
to recall they were also used in one version of the RS components
"make-a-switch" kit.
As far as I can tell from the manual though and unless I'm missing
something, which isn't entirely unkown:-), the voltage reference consists of a
pair of zener diodes rather than a Weston cell.
Either way, I've just discovered one of the switches is jammed, the wafers
look ok and I don't recall it being jammed when I bought it so not sure why
yet, but there goes what I already had planned for today:-)
Regards
Nigel
GM8PZR
In a message dated 07/08/2013 07:37:44 GMT Daylight Time,
robert8rpi@yahoo.co.uk writes:
Hi Joe,
The 893 is worth having as a working instrument. The older ones are
collectibles (possibly) or a source of parts. The Voltage reference is a Weston
cell which will be well past it's expected life. In particular these meters
have a Kelvin Varley voltage divider. This can be used without the meter
section working, possibly recased. The plastic switch dials/drums do tend to
crack or warp due to srinkage of the plastic though. If theK-V dividers
switches are worn out, they are still a good source for precision matched
resistors. Perhaps not spot on value but all the resistors in a decade will be
very close in value. These can be used for voltage dividers and Hamon
resistor units (google Hamon resistor and see
http://conradhoffman.com/HamonResistor.html). They may not look much but are high performance. There are
other precision resitors in these units Take care when removing them, don't
apply any force or stress to the resistor body as this can affect
their performance.
Robert G8RPI.
From: Joseph Gray jgray@zianet.com
To: Discussion of precise voltage measurement volt-nuts@febo.com
Sent: Wednesday, 7 August 2013, 6:00
Subject: [volt-nuts] Fluke differential meters
The local surplus guy has at least three different differential meters that
have been collecting dust for decades. I have borrowed two of them (so
far).
The first one is a Fluke 893A and is solid state. Although it appears to
work, it fails the very first of the performance tests. Now that I have a
full manual, I'm going to look at this a bit closer.
The second one is a Fluke 803B (I think. There is no label on it). It has
tubes. I am slowly bringing it up on a variac before messing with it. I
plan to open it up later and take a good look.
I'm not sure what the third model is, but it looks like it may be an even
older Fluke. It is on a high shelf and I haven't gone over there to lift it
down yet. I'll probably do that later this week.
At the moment, I'm just playing around with this gear and learning a few
things. In the long run, are these things worth having?
Joe Gray
W5JG
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.