DM
Dave M
Mon, Aug 4, 2014 5:05 PM
From: Randy Evans randyevans2688@gmail.com
I am looking at modifying my (defective) HP419A and Fluke 845A Null
meters
using the LTC2054 zero drift op amp. I am planning on using a single
4.2 V
Lithium Ion battery to power them (no AC input required and may not
include, TBD). The LTC2054 has a very low bias current of typically
1pA at
room temp and the bias plots vs. temp show no appreciable increase
until
about 50C. Conceptually, it looks pretty straight forward and, based
on my
Fluke 887A modifications, likely will be very stable.
Since this is a very astute group, does anyone have any comments on
the
feasibility of this modification before I get too involved?
Regards,
Randy Evans
Hi Randy. Good to hear from you again.
I have modified two 883A models and one 887A model DMMs using your details,
with great results. I have a model 845A null meter that is working fine
right now, but who knows how long that will last. I would surely welcome
some research on modifying it with a zero-drift opamp. One concern that I
would have with that mod would be that some mechanism would need to be added
to retain the isolation of the recorder output and guard integrity that's
afforded by the photo-modulator/demodulator circuit. Perhaps some kind of
optically-isolated interface might be in order
Some Spice runs on the original circuit would be interesting to see.
Dave M
> From: Randy Evans <randyevans2688@gmail.com>
>
> I am looking at modifying my (defective) HP419A and Fluke 845A Null
> meters
> using the LTC2054 zero drift op amp. I am planning on using a single
> 4.2 V
> Lithium Ion battery to power them (no AC input required and may not
> include, TBD). The LTC2054 has a very low bias current of typically
> 1pA at
> room temp and the bias plots vs. temp show no appreciable increase
> until
> about 50C. Conceptually, it looks pretty straight forward and, based
> on my
> Fluke 887A modifications, likely will be very stable.
>
> Since this is a very astute group, does anyone have any comments on
> the
> feasibility of this modification before I get too involved?
>
> Regards,
>
> Randy Evans
Hi Randy. Good to hear from you again.
I have modified two 883A models and one 887A model DMMs using your details,
with great results. I have a model 845A null meter that is working fine
right now, but who knows how long that will last. I would surely welcome
some research on modifying it with a zero-drift opamp. One concern that I
would have with that mod would be that some mechanism would need to be added
to retain the isolation of the recorder output and guard integrity that's
afforded by the photo-modulator/demodulator circuit. Perhaps some kind of
optically-isolated interface might be in order
Some Spice runs on the original circuit would be interesting to see.
Dave M
RE
Randy Evans
Mon, Aug 4, 2014 11:27 PM
Dave,
I am investigating some ideas for an isolation circuit for the 845A but the
first priority is to modify the HP-419A first, which doesn't have the
isolated recorder output. I want to use an isolation circuit that draws
very little current and can run on a single lithium battery. Not a trivial
design. The DC offset circuit of the HP-419A will use another lithium-ion
battery with a linear regulator to work over a wide range of battery
voltages is my current thinking.
Randy
On Mon, Aug 4, 2014 at 10:05 AM, Dave M dgminala@mediacombb.net wrote:
I am looking at modifying my (defective) HP419A and Fluke 845A Null
meters
using the LTC2054 zero drift op amp. I am planning on using a single
4.2 V
Lithium Ion battery to power them (no AC input required and may not
include, TBD). The LTC2054 has a very low bias current of typically
1pA at
room temp and the bias plots vs. temp show no appreciable increase
until
about 50C. Conceptually, it looks pretty straight forward and, based
on my
Fluke 887A modifications, likely will be very stable.
Since this is a very astute group, does anyone have any comments on
the
feasibility of this modification before I get too involved?
Regards,
Randy Evans
Hi Randy. Good to hear from you again.
I have modified two 883A models and one 887A model DMMs using your
details, with great results. I have a model 845A null meter that is
working fine right now, but who knows how long that will last. I would
surely welcome some research on modifying it with a zero-drift opamp. One
concern that I would have with that mod would be that some mechanism would
need to be added to retain the isolation of the recorder output and guard
integrity that's afforded by the photo-modulator/demodulator circuit.
Perhaps some kind of optically-isolated interface might be in order
Some Spice runs on the original circuit would be interesting to see.
Dave M
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.
Dave,
I am investigating some ideas for an isolation circuit for the 845A but the
first priority is to modify the HP-419A first, which doesn't have the
isolated recorder output. I want to use an isolation circuit that draws
very little current and can run on a single lithium battery. Not a trivial
design. The DC offset circuit of the HP-419A will use another lithium-ion
battery with a linear regulator to work over a wide range of battery
voltages is my current thinking.
Randy
On Mon, Aug 4, 2014 at 10:05 AM, Dave M <dgminala@mediacombb.net> wrote:
> From: Randy Evans <randyevans2688@gmail.com>
>>
>>
>> I am looking at modifying my (defective) HP419A and Fluke 845A Null
>> meters
>> using the LTC2054 zero drift op amp. I am planning on using a single
>> 4.2 V
>> Lithium Ion battery to power them (no AC input required and may not
>> include, TBD). The LTC2054 has a very low bias current of typically
>> 1pA at
>> room temp and the bias plots vs. temp show no appreciable increase
>> until
>> about 50C. Conceptually, it looks pretty straight forward and, based
>> on my
>> Fluke 887A modifications, likely will be very stable.
>>
>> Since this is a very astute group, does anyone have any comments on
>> the
>> feasibility of this modification before I get too involved?
>>
>> Regards,
>>
>> Randy Evans
>>
>
>
> Hi Randy. Good to hear from you again.
> I have modified two 883A models and one 887A model DMMs using your
> details, with great results. I have a model 845A null meter that is
> working fine right now, but who knows how long that will last. I would
> surely welcome some research on modifying it with a zero-drift opamp. One
> concern that I would have with that mod would be that some mechanism would
> need to be added to retain the isolation of the recorder output and guard
> integrity that's afforded by the photo-modulator/demodulator circuit.
> Perhaps some kind of optically-isolated interface might be in order
>
> Some Spice runs on the original circuit would be interesting to see.
>
> Dave M
>
> _______________________________________________
> 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.
>
RE
Randy Evans
Sat, Aug 9, 2014 2:23 AM
For those interested, I have largely finished the design of the HP-419A
modifications to replace the current active circuits with a more modern
chopper amp; e.g., LTC2054. The LTSpice analysis shows the circuit draws
0.3 mA at full scale meter readings using a single 6V battery. I think I
will use a 6V 225mAH NiCad rechargeable battery (because I have some) that
should last many many hours on one charge. I am still working out the
board layout and unit mods but the circuit is extremely simple and will use
all the existing range and mode switching circuits. The circuit should
also work for the Fluke 845 also. Keep tuned.
Randy
On Mon, Aug 4, 2014 at 10:05 AM, Dave M dgminala@mediacombb.net wrote:
I am looking at modifying my (defective) HP419A and Fluke 845A Null
meters
using the LTC2054 zero drift op amp. I am planning on using a single
4.2 V
Lithium Ion battery to power them (no AC input required and may not
include, TBD). The LTC2054 has a very low bias current of typically
1pA at
room temp and the bias plots vs. temp show no appreciable increase
until
about 50C. Conceptually, it looks pretty straight forward and, based
on my
Fluke 887A modifications, likely will be very stable.
Since this is a very astute group, does anyone have any comments on
the
feasibility of this modification before I get too involved?
Regards,
Randy Evans
Hi Randy. Good to hear from you again.
I have modified two 883A models and one 887A model DMMs using your
details, with great results. I have a model 845A null meter that is
working fine right now, but who knows how long that will last. I would
surely welcome some research on modifying it with a zero-drift opamp. One
concern that I would have with that mod would be that some mechanism would
need to be added to retain the isolation of the recorder output and guard
integrity that's afforded by the photo-modulator/demodulator circuit.
Perhaps some kind of optically-isolated interface might be in order
Some Spice runs on the original circuit would be interesting to see.
Dave M
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.
For those interested, I have largely finished the design of the HP-419A
modifications to replace the current active circuits with a more modern
chopper amp; e.g., LTC2054. The LTSpice analysis shows the circuit draws
0.3 mA at full scale meter readings using a single 6V battery. I think I
will use a 6V 225mAH NiCad rechargeable battery (because I have some) that
should last many many hours on one charge. I am still working out the
board layout and unit mods but the circuit is extremely simple and will use
all the existing range and mode switching circuits. The circuit should
also work for the Fluke 845 also. Keep tuned.
Randy
On Mon, Aug 4, 2014 at 10:05 AM, Dave M <dgminala@mediacombb.net> wrote:
> From: Randy Evans <randyevans2688@gmail.com>
>>
>>
>> I am looking at modifying my (defective) HP419A and Fluke 845A Null
>> meters
>> using the LTC2054 zero drift op amp. I am planning on using a single
>> 4.2 V
>> Lithium Ion battery to power them (no AC input required and may not
>> include, TBD). The LTC2054 has a very low bias current of typically
>> 1pA at
>> room temp and the bias plots vs. temp show no appreciable increase
>> until
>> about 50C. Conceptually, it looks pretty straight forward and, based
>> on my
>> Fluke 887A modifications, likely will be very stable.
>>
>> Since this is a very astute group, does anyone have any comments on
>> the
>> feasibility of this modification before I get too involved?
>>
>> Regards,
>>
>> Randy Evans
>>
>
>
> Hi Randy. Good to hear from you again.
> I have modified two 883A models and one 887A model DMMs using your
> details, with great results. I have a model 845A null meter that is
> working fine right now, but who knows how long that will last. I would
> surely welcome some research on modifying it with a zero-drift opamp. One
> concern that I would have with that mod would be that some mechanism would
> need to be added to retain the isolation of the recorder output and guard
> integrity that's afforded by the photo-modulator/demodulator circuit.
> Perhaps some kind of optically-isolated interface might be in order
>
> Some Spice runs on the original circuit would be interesting to see.
>
> Dave M
>
> _______________________________________________
> 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.
>
TM
Todd Micallef
Sat, Aug 9, 2014 2:48 PM
Randy,
I am looking forward to your test results. Does your 845 have the separate
board for the chopper amp as mentioned in the change/errata sheet dated
7/93? I have not seen any further documents from online sources that
references this change. I have two AR models and it appears support for it
was dropped long before 1993. It would be interesting to see how many of
the original parts were removed and how this new board was mounted inside
the AB chassis.
Todd
On Fri, Aug 8, 2014 at 10:23 PM, Randy Evans randyevans2688@gmail.com
wrote:
For those interested, I have largely finished the design of the HP-419A
modifications to replace the current active circuits with a more modern
chopper amp; e.g., LTC2054. The LTSpice analysis shows the circuit draws
0.3 mA at full scale meter readings using a single 6V battery. I think I
will use a 6V 225mAH NiCad rechargeable battery (because I have some) that
should last many many hours on one charge. I am still working out the
board layout and unit mods but the circuit is extremely simple and will use
all the existing range and mode switching circuits. The circuit should
also work for the Fluke 845 also. Keep tuned.
Randy
On Mon, Aug 4, 2014 at 10:05 AM, Dave M dgminala@mediacombb.net wrote:
I am looking at modifying my (defective) HP419A and Fluke 845A Null
meters
using the LTC2054 zero drift op amp. I am planning on using a single
4.2 V
Lithium Ion battery to power them (no AC input required and may not
include, TBD). The LTC2054 has a very low bias current of typically
1pA at
room temp and the bias plots vs. temp show no appreciable increase
until
about 50C. Conceptually, it looks pretty straight forward and, based
on my
Fluke 887A modifications, likely will be very stable.
Since this is a very astute group, does anyone have any comments on
the
feasibility of this modification before I get too involved?
Regards,
Randy Evans
Hi Randy. Good to hear from you again.
I have modified two 883A models and one 887A model DMMs using your
details, with great results. I have a model 845A null meter that is
working fine right now, but who knows how long that will last. I would
surely welcome some research on modifying it with a zero-drift opamp.
concern that I would have with that mod would be that some mechanism
need to be added to retain the isolation of the recorder output and guard
integrity that's afforded by the photo-modulator/demodulator circuit.
Perhaps some kind of optically-isolated interface might be in order
Some Spice runs on the original circuit would be interesting to see.
Dave M
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.
Randy,
I am looking forward to your test results. Does your 845 have the separate
board for the chopper amp as mentioned in the change/errata sheet dated
7/93? I have not seen any further documents from online sources that
references this change. I have two AR models and it appears support for it
was dropped long before 1993. It would be interesting to see how many of
the original parts were removed and how this new board was mounted inside
the AB chassis.
Todd
On Fri, Aug 8, 2014 at 10:23 PM, Randy Evans <randyevans2688@gmail.com>
wrote:
> For those interested, I have largely finished the design of the HP-419A
> modifications to replace the current active circuits with a more modern
> chopper amp; e.g., LTC2054. The LTSpice analysis shows the circuit draws
> 0.3 mA at full scale meter readings using a single 6V battery. I think I
> will use a 6V 225mAH NiCad rechargeable battery (because I have some) that
> should last many many hours on one charge. I am still working out the
> board layout and unit mods but the circuit is extremely simple and will use
> all the existing range and mode switching circuits. The circuit should
> also work for the Fluke 845 also. Keep tuned.
>
> Randy
>
>
> On Mon, Aug 4, 2014 at 10:05 AM, Dave M <dgminala@mediacombb.net> wrote:
>
> > From: Randy Evans <randyevans2688@gmail.com>
> >>
> >>
> >> I am looking at modifying my (defective) HP419A and Fluke 845A Null
> >> meters
> >> using the LTC2054 zero drift op amp. I am planning on using a single
> >> 4.2 V
> >> Lithium Ion battery to power them (no AC input required and may not
> >> include, TBD). The LTC2054 has a very low bias current of typically
> >> 1pA at
> >> room temp and the bias plots vs. temp show no appreciable increase
> >> until
> >> about 50C. Conceptually, it looks pretty straight forward and, based
> >> on my
> >> Fluke 887A modifications, likely will be very stable.
> >>
> >> Since this is a very astute group, does anyone have any comments on
> >> the
> >> feasibility of this modification before I get too involved?
> >>
> >> Regards,
> >>
> >> Randy Evans
> >>
> >
> >
> > Hi Randy. Good to hear from you again.
> > I have modified two 883A models and one 887A model DMMs using your
> > details, with great results. I have a model 845A null meter that is
> > working fine right now, but who knows how long that will last. I would
> > surely welcome some research on modifying it with a zero-drift opamp.
> One
> > concern that I would have with that mod would be that some mechanism
> would
> > need to be added to retain the isolation of the recorder output and guard
> > integrity that's afforded by the photo-modulator/demodulator circuit.
> > Perhaps some kind of optically-isolated interface might be in order
> >
> > Some Spice runs on the original circuit would be interesting to see.
> >
> > Dave M
> >
> > _______________________________________________
> > 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.
>
RE
Randy Evans
Sat, Aug 9, 2014 6:48 PM
Todd,
My 845 has the optical chopper circuit. It quasi-works but the most
sensitive ranges are very noisy so I will replace the amplifier circuits
with a new chopper stabilized circuit after I finish the 419 modifications.
Randy
On Sat, Aug 9, 2014 at 7:48 AM, Todd Micallef tmicallef@gmail.com wrote:
Randy,
I am looking forward to your test results. Does your 845 have the separate
board for the chopper amp as mentioned in the change/errata sheet dated
7/93? I have not seen any further documents from online sources that
references this change. I have two AR models and it appears support for it
was dropped long before 1993. It would be interesting to see how many of
the original parts were removed and how this new board was mounted inside
the AB chassis.
Todd
On Fri, Aug 8, 2014 at 10:23 PM, Randy Evans randyevans2688@gmail.com
wrote:
For those interested, I have largely finished the design of the HP-419A
modifications to replace the current active circuits with a more modern
chopper amp; e.g., LTC2054. The LTSpice analysis shows the circuit draws
0.3 mA at full scale meter readings using a single 6V battery. I think I
will use a 6V 225mAH NiCad rechargeable battery (because I have some)
should last many many hours on one charge. I am still working out the
board layout and unit mods but the circuit is extremely simple and will
all the existing range and mode switching circuits. The circuit should
also work for the Fluke 845 also. Keep tuned.
Randy
On Mon, Aug 4, 2014 at 10:05 AM, Dave M dgminala@mediacombb.net wrote:
I am looking at modifying my (defective) HP419A and Fluke 845A Null
meters
using the LTC2054 zero drift op amp. I am planning on using a single
4.2 V
Lithium Ion battery to power them (no AC input required and may not
include, TBD). The LTC2054 has a very low bias current of typically
1pA at
room temp and the bias plots vs. temp show no appreciable increase
until
about 50C. Conceptually, it looks pretty straight forward and, based
on my
Fluke 887A modifications, likely will be very stable.
Since this is a very astute group, does anyone have any comments on
the
feasibility of this modification before I get too involved?
Regards,
Randy Evans
Hi Randy. Good to hear from you again.
I have modified two 883A models and one 887A model DMMs using your
details, with great results. I have a model 845A null meter that is
working fine right now, but who knows how long that will last. I would
surely welcome some research on modifying it with a zero-drift opamp.
concern that I would have with that mod would be that some mechanism
need to be added to retain the isolation of the recorder output and
integrity that's afforded by the photo-modulator/demodulator circuit.
Perhaps some kind of optically-isolated interface might be in order
Some Spice runs on the original circuit would be interesting to see.
Dave M
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.
Todd,
My 845 has the optical chopper circuit. It quasi-works but the most
sensitive ranges are very noisy so I will replace the amplifier circuits
with a new chopper stabilized circuit after I finish the 419 modifications.
Randy
On Sat, Aug 9, 2014 at 7:48 AM, Todd Micallef <tmicallef@gmail.com> wrote:
> Randy,
>
> I am looking forward to your test results. Does your 845 have the separate
> board for the chopper amp as mentioned in the change/errata sheet dated
> 7/93? I have not seen any further documents from online sources that
> references this change. I have two AR models and it appears support for it
> was dropped long before 1993. It would be interesting to see how many of
> the original parts were removed and how this new board was mounted inside
> the AB chassis.
>
>
> Todd
>
>
> On Fri, Aug 8, 2014 at 10:23 PM, Randy Evans <randyevans2688@gmail.com>
> wrote:
>
> > For those interested, I have largely finished the design of the HP-419A
> > modifications to replace the current active circuits with a more modern
> > chopper amp; e.g., LTC2054. The LTSpice analysis shows the circuit draws
> > 0.3 mA at full scale meter readings using a single 6V battery. I think I
> > will use a 6V 225mAH NiCad rechargeable battery (because I have some)
> that
> > should last many many hours on one charge. I am still working out the
> > board layout and unit mods but the circuit is extremely simple and will
> use
> > all the existing range and mode switching circuits. The circuit should
> > also work for the Fluke 845 also. Keep tuned.
> >
> > Randy
> >
> >
> > On Mon, Aug 4, 2014 at 10:05 AM, Dave M <dgminala@mediacombb.net> wrote:
> >
> > > From: Randy Evans <randyevans2688@gmail.com>
> > >>
> > >>
> > >> I am looking at modifying my (defective) HP419A and Fluke 845A Null
> > >> meters
> > >> using the LTC2054 zero drift op amp. I am planning on using a single
> > >> 4.2 V
> > >> Lithium Ion battery to power them (no AC input required and may not
> > >> include, TBD). The LTC2054 has a very low bias current of typically
> > >> 1pA at
> > >> room temp and the bias plots vs. temp show no appreciable increase
> > >> until
> > >> about 50C. Conceptually, it looks pretty straight forward and, based
> > >> on my
> > >> Fluke 887A modifications, likely will be very stable.
> > >>
> > >> Since this is a very astute group, does anyone have any comments on
> > >> the
> > >> feasibility of this modification before I get too involved?
> > >>
> > >> Regards,
> > >>
> > >> Randy Evans
> > >>
> > >
> > >
> > > Hi Randy. Good to hear from you again.
> > > I have modified two 883A models and one 887A model DMMs using your
> > > details, with great results. I have a model 845A null meter that is
> > > working fine right now, but who knows how long that will last. I would
> > > surely welcome some research on modifying it with a zero-drift opamp.
> > One
> > > concern that I would have with that mod would be that some mechanism
> > would
> > > need to be added to retain the isolation of the recorder output and
> guard
> > > integrity that's afforded by the photo-modulator/demodulator circuit.
> > > Perhaps some kind of optically-isolated interface might be in order
> > >
> > > Some Spice runs on the original circuit would be interesting to see.
> > >
> > > Dave M
> > >
> > > _______________________________________________
> > > 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.
>
LL
Ludger.Lenzen@gmx.de
Wed, Nov 26, 2014 12:06 PM
RE
Randy Evans
Wed, Nov 26, 2014 5:18 PM
I have finished the design and analysis (LTSpice) and I am preparing the
BOM and doing a PCB layout now (ExpressPCB). I am hoping to finish the
work over the Thanksgiving holidays but I wanted to see Dallas's 845A
modifications before ordering parts and pulling the plug on PCB fab first
but it hasn't shown up on K04BB's site yet (still in the upload section).
Randy
On Wed, Nov 26, 2014 at 4:06 AM, Ludger.Lenzen@gmx.de wrote:
Hi Randy,
did you finish the HP-419A modification with a modern chopper amp?
I have to refurbish my HP-419A so it would make sense to replace the
optical chopper. Any help or made expericance would perfect.
BR
Ludger / PeLuLe
Gesendet: Samstag, 09. August 2014 um 03:23 Uhr
Von: "Randy Evans" randyevans2688@gmail.com
An: "Discussion of precise voltage measurement" volt-nuts@febo.com
Betreff: Re: [volt-nuts] HP-419 and Fluke 845 Modifications
For those interested, I have largely finished the design of the HP-419A
modifications to replace the current active circuits with a more modern
chopper amp; e.g., LTC2054. The LTSpice analysis shows the circuit draws
0.3 mA at full scale meter readings using a single 6V battery. I think I
will use a 6V 225mAH NiCad rechargeable battery (because I have some) that
should last many many hours on one charge. I am still working out the
board layout and unit mods but the circuit is extremely simple and will use
all the existing range and mode switching circuits. The circuit should
also work for the Fluke 845 also. Keep tuned.
Randy
On Mon, Aug 4, 2014 at 10:05 AM, Dave M dgminala@mediacombb.net wrote:
I am looking at modifying my (defective) HP419A and Fluke 845A Null
meters
using the LTC2054 zero drift op amp. I am planning on using a single
4.2 V
Lithium Ion battery to power them (no AC input required and may not
include, TBD). The LTC2054 has a very low bias current of typically
1pA at
room temp and the bias plots vs. temp show no appreciable increase
until
about 50C. Conceptually, it looks pretty straight forward and, based
on my
Fluke 887A modifications, likely will be very stable.
Since this is a very astute group, does anyone have any comments on
the
feasibility of this modification before I get too involved?
Regards,
Randy Evans
Hi Randy. Good to hear from you again.
I have modified two 883A models and one 887A model DMMs using your
details, with great results. I have a model 845A null meter that is
working fine right now, but who knows how long that will last. I would
surely welcome some research on modifying it with a zero-drift opamp. One
concern that I would have with that mod would be that some mechanism
need to be added to retain the isolation of the recorder output and guard
integrity that's afforded by the photo-modulator/demodulator circuit.
Perhaps some kind of optically-isolated interface might be in order
Some Spice runs on the original circuit would be interesting to see.
Dave M
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.
I have finished the design and analysis (LTSpice) and I am preparing the
BOM and doing a PCB layout now (ExpressPCB). I am hoping to finish the
work over the Thanksgiving holidays but I wanted to see Dallas's 845A
modifications before ordering parts and pulling the plug on PCB fab first
but it hasn't shown up on K04BB's site yet (still in the upload section).
Randy
On Wed, Nov 26, 2014 at 4:06 AM, <Ludger.Lenzen@gmx.de> wrote:
> Hi Randy,
>
> did you finish the HP-419A modification with a modern chopper amp?
>
> I have to refurbish my HP-419A so it would make sense to replace the
> optical chopper. Any help or made expericance would perfect.
>
> BR
> Ludger / PeLuLe
>
> *Gesendet:* Samstag, 09. August 2014 um 03:23 Uhr
> *Von:* "Randy Evans" <randyevans2688@gmail.com>
> *An:* "Discussion of precise voltage measurement" <volt-nuts@febo.com>
> *Betreff:* Re: [volt-nuts] HP-419 and Fluke 845 Modifications
> For those interested, I have largely finished the design of the HP-419A
> modifications to replace the current active circuits with a more modern
> chopper amp; e.g., LTC2054. The LTSpice analysis shows the circuit draws
> 0.3 mA at full scale meter readings using a single 6V battery. I think I
> will use a 6V 225mAH NiCad rechargeable battery (because I have some) that
> should last many many hours on one charge. I am still working out the
> board layout and unit mods but the circuit is extremely simple and will use
> all the existing range and mode switching circuits. The circuit should
> also work for the Fluke 845 also. Keep tuned.
>
> Randy
>
>
> On Mon, Aug 4, 2014 at 10:05 AM, Dave M <dgminala@mediacombb.net> wrote:
>
> > From: Randy Evans <randyevans2688@gmail.com>
> >>
> >>
> >> I am looking at modifying my (defective) HP419A and Fluke 845A Null
> >> meters
> >> using the LTC2054 zero drift op amp. I am planning on using a single
> >> 4.2 V
> >> Lithium Ion battery to power them (no AC input required and may not
> >> include, TBD). The LTC2054 has a very low bias current of typically
> >> 1pA at
> >> room temp and the bias plots vs. temp show no appreciable increase
> >> until
> >> about 50C. Conceptually, it looks pretty straight forward and, based
> >> on my
> >> Fluke 887A modifications, likely will be very stable.
> >>
> >> Since this is a very astute group, does anyone have any comments on
> >> the
> >> feasibility of this modification before I get too involved?
> >>
> >> Regards,
> >>
> >> Randy Evans
> >>
> >
> >
> > Hi Randy. Good to hear from you again.
> > I have modified two 883A models and one 887A model DMMs using your
> > details, with great results. I have a model 845A null meter that is
> > working fine right now, but who knows how long that will last. I would
> > surely welcome some research on modifying it with a zero-drift opamp. One
> > concern that I would have with that mod would be that some mechanism
> would
> > need to be added to retain the isolation of the recorder output and guard
> > integrity that's afforded by the photo-modulator/demodulator circuit.
> > Perhaps some kind of optically-isolated interface might be in order
> >
> > Some Spice runs on the original circuit would be interesting to see.
> >
> > Dave M
> >
> > _______________________________________________
> > 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.
>
TM
Todd Micallef
Wed, Nov 26, 2014 5:45 PM
Randy,
I sent you a copy of the file to your email address.
Todd
On Wed, Nov 26, 2014 at 12:18 PM, Randy Evans randyevans2688@gmail.com
wrote:
I have finished the design and analysis (LTSpice) and I am preparing the
BOM and doing a PCB layout now (ExpressPCB). I am hoping to finish the
work over the Thanksgiving holidays but I wanted to see Dallas's 845A
modifications before ordering parts and pulling the plug on PCB fab first
but it hasn't shown up on K04BB's site yet (still in the upload section).
Randy
On Wed, Nov 26, 2014 at 4:06 AM, Ludger.Lenzen@gmx.de wrote:
Hi Randy,
did you finish the HP-419A modification with a modern chopper amp?
I have to refurbish my HP-419A so it would make sense to replace the
optical chopper. Any help or made expericance would perfect.
BR
Ludger / PeLuLe
Gesendet: Samstag, 09. August 2014 um 03:23 Uhr
Von: "Randy Evans" randyevans2688@gmail.com
An: "Discussion of precise voltage measurement" volt-nuts@febo.com
Betreff: Re: [volt-nuts] HP-419 and Fluke 845 Modifications
For those interested, I have largely finished the design of the HP-419A
modifications to replace the current active circuits with a more modern
chopper amp; e.g., LTC2054. The LTSpice analysis shows the circuit draws
0.3 mA at full scale meter readings using a single 6V battery. I think I
will use a 6V 225mAH NiCad rechargeable battery (because I have some)
should last many many hours on one charge. I am still working out the
board layout and unit mods but the circuit is extremely simple and will
all the existing range and mode switching circuits. The circuit should
also work for the Fluke 845 also. Keep tuned.
Randy
On Mon, Aug 4, 2014 at 10:05 AM, Dave M dgminala@mediacombb.net wrote:
I am looking at modifying my (defective) HP419A and Fluke 845A Null
meters
using the LTC2054 zero drift op amp. I am planning on using a single
4.2 V
Lithium Ion battery to power them (no AC input required and may not
include, TBD). The LTC2054 has a very low bias current of typically
1pA at
room temp and the bias plots vs. temp show no appreciable increase
until
about 50C. Conceptually, it looks pretty straight forward and, based
on my
Fluke 887A modifications, likely will be very stable.
Since this is a very astute group, does anyone have any comments on
the
feasibility of this modification before I get too involved?
Regards,
Randy Evans
Hi Randy. Good to hear from you again.
I have modified two 883A models and one 887A model DMMs using your
details, with great results. I have a model 845A null meter that is
working fine right now, but who knows how long that will last. I would
surely welcome some research on modifying it with a zero-drift opamp.
concern that I would have with that mod would be that some mechanism
need to be added to retain the isolation of the recorder output and
integrity that's afforded by the photo-modulator/demodulator circuit.
Perhaps some kind of optically-isolated interface might be in order
Some Spice runs on the original circuit would be interesting to see.
Dave M
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.
Randy,
I sent you a copy of the file to your email address.
Todd
On Wed, Nov 26, 2014 at 12:18 PM, Randy Evans <randyevans2688@gmail.com>
wrote:
> I have finished the design and analysis (LTSpice) and I am preparing the
> BOM and doing a PCB layout now (ExpressPCB). I am hoping to finish the
> work over the Thanksgiving holidays but I wanted to see Dallas's 845A
> modifications before ordering parts and pulling the plug on PCB fab first
> but it hasn't shown up on K04BB's site yet (still in the upload section).
>
> Randy
>
> On Wed, Nov 26, 2014 at 4:06 AM, <Ludger.Lenzen@gmx.de> wrote:
>
> > Hi Randy,
> >
> > did you finish the HP-419A modification with a modern chopper amp?
> >
> > I have to refurbish my HP-419A so it would make sense to replace the
> > optical chopper. Any help or made expericance would perfect.
> >
> > BR
> > Ludger / PeLuLe
> >
> > *Gesendet:* Samstag, 09. August 2014 um 03:23 Uhr
> > *Von:* "Randy Evans" <randyevans2688@gmail.com>
> > *An:* "Discussion of precise voltage measurement" <volt-nuts@febo.com>
> > *Betreff:* Re: [volt-nuts] HP-419 and Fluke 845 Modifications
> > For those interested, I have largely finished the design of the HP-419A
> > modifications to replace the current active circuits with a more modern
> > chopper amp; e.g., LTC2054. The LTSpice analysis shows the circuit draws
> > 0.3 mA at full scale meter readings using a single 6V battery. I think I
> > will use a 6V 225mAH NiCad rechargeable battery (because I have some)
> that
> > should last many many hours on one charge. I am still working out the
> > board layout and unit mods but the circuit is extremely simple and will
> use
> > all the existing range and mode switching circuits. The circuit should
> > also work for the Fluke 845 also. Keep tuned.
> >
> > Randy
> >
> >
> > On Mon, Aug 4, 2014 at 10:05 AM, Dave M <dgminala@mediacombb.net> wrote:
> >
> > > From: Randy Evans <randyevans2688@gmail.com>
> > >>
> > >>
> > >> I am looking at modifying my (defective) HP419A and Fluke 845A Null
> > >> meters
> > >> using the LTC2054 zero drift op amp. I am planning on using a single
> > >> 4.2 V
> > >> Lithium Ion battery to power them (no AC input required and may not
> > >> include, TBD). The LTC2054 has a very low bias current of typically
> > >> 1pA at
> > >> room temp and the bias plots vs. temp show no appreciable increase
> > >> until
> > >> about 50C. Conceptually, it looks pretty straight forward and, based
> > >> on my
> > >> Fluke 887A modifications, likely will be very stable.
> > >>
> > >> Since this is a very astute group, does anyone have any comments on
> > >> the
> > >> feasibility of this modification before I get too involved?
> > >>
> > >> Regards,
> > >>
> > >> Randy Evans
> > >>
> > >
> > >
> > > Hi Randy. Good to hear from you again.
> > > I have modified two 883A models and one 887A model DMMs using your
> > > details, with great results. I have a model 845A null meter that is
> > > working fine right now, but who knows how long that will last. I would
> > > surely welcome some research on modifying it with a zero-drift opamp.
> One
> > > concern that I would have with that mod would be that some mechanism
> > would
> > > need to be added to retain the isolation of the recorder output and
> guard
> > > integrity that's afforded by the photo-modulator/demodulator circuit.
> > > Perhaps some kind of optically-isolated interface might be in order
> > >
> > > Some Spice runs on the original circuit would be interesting to see.
> > >
> > > Dave M
> > >
> > > _______________________________________________
> > > 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.
>
DS
Dallas Smith
Wed, Nov 26, 2014 5:52 PM
Randy,
You can access the files by entering 'ftp://ftp.ko4bb.com/' in windows
explorer ( not IE), then supply the user name password.
username: manuals
password: ko4bb2014
Dallas
On 11/26/2014 12:18 PM, Randy Evans wrote:
I have finished the design and analysis (LTSpice) and I am preparing the
BOM and doing a PCB layout now (ExpressPCB). I am hoping to finish the
work over the Thanksgiving holidays but I wanted to see Dallas's 845A
modifications before ordering parts and pulling the plug on PCB fab first
but it hasn't shown up on K04BB's site yet (still in the upload section).
Randy
On Wed, Nov 26, 2014 at 4:06 AM, Ludger.Lenzen@gmx.de wrote:
Randy,
You can access the files by entering 'ftp://ftp.ko4bb.com/' in windows
explorer ( not IE), then supply the user name password.
username: manuals
password: ko4bb2014
Dallas
On 11/26/2014 12:18 PM, Randy Evans wrote:
> I have finished the design and analysis (LTSpice) and I am preparing the
> BOM and doing a PCB layout now (ExpressPCB). I am hoping to finish the
> work over the Thanksgiving holidays but I wanted to see Dallas's 845A
> modifications before ordering parts and pulling the plug on PCB fab first
> but it hasn't shown up on K04BB's site yet (still in the upload section).
>
> Randy
>
> On Wed, Nov 26, 2014 at 4:06 AM, <Ludger.Lenzen@gmx.de> wrote:
DS
Dallas Smith
Wed, Nov 26, 2014 5:53 PM
The current version has been updated, also is in a word document.
Dallas
On 11/26/2014 12:45 PM, Todd Micallef wrote:
Randy,
I sent you a copy of the file to your email address.
Todd
On Wed, Nov 26, 2014 at 12:18 PM, Randy Evans randyevans2688@gmail.com
wrote:
The current version has been updated, also is in a word document.
Dallas
On 11/26/2014 12:45 PM, Todd Micallef wrote:
> Randy,
>
> I sent you a copy of the file to your email address.
>
> Todd
>
> On Wed, Nov 26, 2014 at 12:18 PM, Randy Evans <randyevans2688@gmail.com>
> wrote:
>
>
