RE
Randy Evans
Mon, Aug 4, 2014 3:33 PM
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
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
RE
Randy Evans
Mon, Dec 1, 2014 1:17 AM
I finished the H-419A/Fluke 845A design modifications but I am still trying
to decide on the preferred power supply design. The basic meter circuit
uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V batteries. The
basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
batteries should be able to go several thousand hours on a set of
batteries. For the meter circuit, it is always battery powered and
doesn't have to be plugged into the mains.
I also added a TI AMC1100 isolation amplifier for recording output but it
needs a 3.3 VDC isolated supply and a 5VDC output supply. The current
design uses separate isolation power supplies using LT8300 ICs that work
off the mains transformer so there would be no worry about failing
batteries. Therefore, to use the recorder, the unit would have to be
plugged in. I am trying to decide if it would be simpler to use batteries
for the isolation circuit as well. If I use batteries, do I use
rechargeables or non-rechargeable batteries such as the CR123s? The
circuit would need one set for the input isolated circuit side and another
set for the recorder output side and the batteries would not last as long
as the meter circuit since the isolation circuits draw about 12 milliamps.
They would still work about one hundred hours most likely and would not
draw any current unless the isolation circuit is turned on (with a separate
toggle switch). My preference is to stay with the LT8300 power supplies
but I thought I would query the group.
Any thoughts on what would be your preferences?
Thanks,
Randy Evans
On Mon, Aug 4, 2014 at 8:33 AM, Randy Evans randyevans2688@gmail.com
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
I finished the H-419A/Fluke 845A design modifications but I am still trying
to decide on the preferred power supply design. The basic meter circuit
uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V batteries. The
basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
batteries should be able to go several thousand hours on a set of
batteries. For the meter circuit, it is always battery powered and
doesn't have to be plugged into the mains.
I also added a TI AMC1100 isolation amplifier for recording output but it
needs a 3.3 VDC isolated supply and a 5VDC output supply. The current
design uses separate isolation power supplies using LT8300 ICs that work
off the mains transformer so there would be no worry about failing
batteries. Therefore, to use the recorder, the unit would have to be
plugged in. I am trying to decide if it would be simpler to use batteries
for the isolation circuit as well. If I use batteries, do I use
rechargeables or non-rechargeable batteries such as the CR123s? The
circuit would need one set for the input isolated circuit side and another
set for the recorder output side and the batteries would not last as long
as the meter circuit since the isolation circuits draw about 12 milliamps.
They would still work about one hundred hours most likely and would not
draw any current unless the isolation circuit is turned on (with a separate
toggle switch). My preference is to stay with the LT8300 power supplies
but I thought I would query the group.
Any thoughts on what would be your preferences?
Thanks,
Randy Evans
On Mon, Aug 4, 2014 at 8:33 AM, Randy Evans <randyevans2688@gmail.com>
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
>
DM
Dave M
Mon, Dec 1, 2014 2:37 AM
Randy,
Thanks for continuing with this modification.
Speaking of the Fluke 845A;
At first glance, you could probably leave the existing power supply inverter
circuit intact, as well as the isolation transformer for the recorder
output, with the recorder output transformer being driven (at the center
tap) by the output of the last DC amp stage of the null amp circuit. That
would maintain the isolation of the meter and recorder output, and eliminate
the need for an extra amp for them. It would also maintain the guard
integrity, keeping the instrument's operational characteristics as close to
original as possible.
By leaving the existing inverter circuit in place, you can easily derive any
voltages (+ and -) that your mod needs from it, without the need for
additional isolated power supplies
Dave M
Randy Evans wrote:
I finished the H-419A/Fluke 845A design modifications but I am still
trying to decide on the preferred power supply design. The basic
meter circuit uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V
batteries. The
basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
batteries should be able to go several thousand hours on a set of
batteries. For the meter circuit, it is always battery powered and
doesn't have to be plugged into the mains.
I also added a TI AMC1100 isolation amplifier for recording output
but it needs a 3.3 VDC isolated supply and a 5VDC output supply. The
current design uses separate isolation power supplies using LT8300
ICs that work off the mains transformer so there would be no worry
about failing batteries. Therefore, to use the recorder, the unit
would have to be plugged in. I am trying to decide if it would be
simpler to use batteries for the isolation circuit as well. If I use
batteries, do I use rechargeables or non-rechargeable batteries such
as the CR123s? The
circuit would need one set for the input isolated circuit side and
another set for the recorder output side and the batteries would not
last as long
as the meter circuit since the isolation circuits draw about 12
milliamps. They would still work about one hundred hours most likely
and would not
draw any current unless the isolation circuit is turned on (with a
separate toggle switch). My preference is to stay with the LT8300
power supplies
but I thought I would query the group.
Any thoughts on what would be your preferences?
Thanks,
Randy Evans
On Mon, Aug 4, 2014 at 8:33 AM, Randy Evans randyevans2688@gmail.com
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
Randy,
Thanks for continuing with this modification.
Speaking of the Fluke 845A;
At first glance, you could probably leave the existing power supply inverter
circuit intact, as well as the isolation transformer for the recorder
output, with the recorder output transformer being driven (at the center
tap) by the output of the last DC amp stage of the null amp circuit. That
would maintain the isolation of the meter and recorder output, and eliminate
the need for an extra amp for them. It would also maintain the guard
integrity, keeping the instrument's operational characteristics as close to
original as possible.
By leaving the existing inverter circuit in place, you can easily derive any
voltages (+ and -) that your mod needs from it, without the need for
additional isolated power supplies
Dave M
Randy Evans wrote:
> I finished the H-419A/Fluke 845A design modifications but I am still
> trying to decide on the preferred power supply design. The basic
> meter circuit uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V
> batteries. The
> basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
> batteries should be able to go several thousand hours on a set of
> batteries. For the meter circuit, it is always battery powered and
> doesn't have to be plugged into the mains.
>
> I also added a TI AMC1100 isolation amplifier for recording output
> but it needs a 3.3 VDC isolated supply and a 5VDC output supply. The
> current design uses separate isolation power supplies using LT8300
> ICs that work off the mains transformer so there would be no worry
> about failing batteries. Therefore, to use the recorder, the unit
> would have to be plugged in. I am trying to decide if it would be
> simpler to use batteries for the isolation circuit as well. If I use
> batteries, do I use rechargeables or non-rechargeable batteries such
> as the CR123s? The
> circuit would need one set for the input isolated circuit side and
> another set for the recorder output side and the batteries would not
> last as long
> as the meter circuit since the isolation circuits draw about 12
> milliamps. They would still work about one hundred hours most likely
> and would not
> draw any current unless the isolation circuit is turned on (with a
> separate toggle switch). My preference is to stay with the LT8300
> power supplies
> but I thought I would query the group.
>
> Any thoughts on what would be your preferences?
>
> Thanks,
>
> Randy Evans
>
> On Mon, Aug 4, 2014 at 8:33 AM, Randy Evans <randyevans2688@gmail.com>
> 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
RE
Randy Evans
Mon, Dec 1, 2014 7:40 PM
Dave,
The HP-419A is driving the need for an isolated recording output (it
doesn't have one in the basic unit) and I wanted to provide one. The
circuit is being designed to work with either the HP-419A or the Fluke
845A. The isolation circuit does not have to be used if not wanted since
it is a completely separate circuit and not needed for the meter to work.
I still need to work on the final HP-845A modifications and i will look at
your suggestions.
Randy
On Sun, Nov 30, 2014 at 6:37 PM, Dave M dgminala@mediacombb.net wrote:
Randy,
Thanks for continuing with this modification.
Speaking of the Fluke 845A;
At first glance, you could probably leave the existing power supply
inverter circuit intact, as well as the isolation transformer for the
recorder output, with the recorder output transformer being driven (at the
center tap) by the output of the last DC amp stage of the null amp
circuit. That would maintain the isolation of the meter and recorder
output, and eliminate the need for an extra amp for them. It would also
maintain the guard integrity, keeping the instrument's operational
characteristics as close to original as possible.
By leaving the existing inverter circuit in place, you can easily derive
any voltages (+ and -) that your mod needs from it, without the need for
additional isolated power supplies
Dave M
Randy Evans wrote:
I finished the H-419A/Fluke 845A design modifications but I am still
trying to decide on the preferred power supply design. The basic
meter circuit uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V
batteries. The
basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
batteries should be able to go several thousand hours on a set of
batteries. For the meter circuit, it is always battery powered and
doesn't have to be plugged into the mains.
I also added a TI AMC1100 isolation amplifier for recording output
but it needs a 3.3 VDC isolated supply and a 5VDC output supply. The
current design uses separate isolation power supplies using LT8300
ICs that work off the mains transformer so there would be no worry
about failing batteries. Therefore, to use the recorder, the unit
would have to be plugged in. I am trying to decide if it would be
simpler to use batteries for the isolation circuit as well. If I use
batteries, do I use rechargeables or non-rechargeable batteries such
as the CR123s? The
circuit would need one set for the input isolated circuit side and
another set for the recorder output side and the batteries would not
last as long
as the meter circuit since the isolation circuits draw about 12
milliamps. They would still work about one hundred hours most likely
and would not
draw any current unless the isolation circuit is turned on (with a
separate toggle switch). My preference is to stay with the LT8300
power supplies
but I thought I would query the group.
Any thoughts on what would be your preferences?
Thanks,
Randy Evans
On Mon, Aug 4, 2014 at 8:33 AM, Randy Evans randyevans2688@gmail.com
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
Dave,
The HP-419A is driving the need for an isolated recording output (it
doesn't have one in the basic unit) and I wanted to provide one. The
circuit is being designed to work with either the HP-419A or the Fluke
845A. The isolation circuit does not have to be used if not wanted since
it is a completely separate circuit and not needed for the meter to work.
I still need to work on the final HP-845A modifications and i will look at
your suggestions.
Randy
On Sun, Nov 30, 2014 at 6:37 PM, Dave M <dgminala@mediacombb.net> wrote:
> Randy,
> Thanks for continuing with this modification.
>
> Speaking of the Fluke 845A;
> At first glance, you could probably leave the existing power supply
> inverter circuit intact, as well as the isolation transformer for the
> recorder output, with the recorder output transformer being driven (at the
> center tap) by the output of the last DC amp stage of the null amp
> circuit. That would maintain the isolation of the meter and recorder
> output, and eliminate the need for an extra amp for them. It would also
> maintain the guard integrity, keeping the instrument's operational
> characteristics as close to original as possible.
> By leaving the existing inverter circuit in place, you can easily derive
> any voltages (+ and -) that your mod needs from it, without the need for
> additional isolated power supplies
>
> Dave M
>
>
>
> Randy Evans wrote:
>
>> I finished the H-419A/Fluke 845A design modifications but I am still
>> trying to decide on the preferred power supply design. The basic
>> meter circuit uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V
>> batteries. The
>> basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
>> batteries should be able to go several thousand hours on a set of
>> batteries. For the meter circuit, it is always battery powered and
>> doesn't have to be plugged into the mains.
>>
>> I also added a TI AMC1100 isolation amplifier for recording output
>> but it needs a 3.3 VDC isolated supply and a 5VDC output supply. The
>> current design uses separate isolation power supplies using LT8300
>> ICs that work off the mains transformer so there would be no worry
>> about failing batteries. Therefore, to use the recorder, the unit
>> would have to be plugged in. I am trying to decide if it would be
>> simpler to use batteries for the isolation circuit as well. If I use
>> batteries, do I use rechargeables or non-rechargeable batteries such
>> as the CR123s? The
>> circuit would need one set for the input isolated circuit side and
>> another set for the recorder output side and the batteries would not
>> last as long
>> as the meter circuit since the isolation circuits draw about 12
>> milliamps. They would still work about one hundred hours most likely
>> and would not
>> draw any current unless the isolation circuit is turned on (with a
>> separate toggle switch). My preference is to stay with the LT8300
>> power supplies
>> but I thought I would query the group.
>>
>> Any thoughts on what would be your preferences?
>>
>> Thanks,
>>
>> Randy Evans
>>
>> On Mon, Aug 4, 2014 at 8:33 AM, Randy Evans <randyevans2688@gmail.com>
>> 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
>>>
>>
>
> _______________________________________________
> 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.
>
PL
Pete Lancashire
Mon, Dec 1, 2014 7:49 PM
I have used 845As and other instruments recorder output voltage to
digitize what I'm measuring. I'm surprised the 419A doesn't. I just
never looked before. So not like HP, I'm glad your considering adding
one.
On Mon, Dec 1, 2014 at 11:40 AM, Randy Evans randyevans2688@gmail.com wrote:
Dave,
The HP-419A is driving the need for an isolated recording output (it
doesn't have one in the basic unit) and I wanted to provide one. The
circuit is being designed to work with either the HP-419A or the Fluke
845A. The isolation circuit does not have to be used if not wanted since
it is a completely separate circuit and not needed for the meter to work.
I still need to work on the final HP-845A modifications and i will look at
your suggestions.
Randy
On Sun, Nov 30, 2014 at 6:37 PM, Dave M dgminala@mediacombb.net wrote:
Randy,
Thanks for continuing with this modification.
Speaking of the Fluke 845A;
At first glance, you could probably leave the existing power supply
inverter circuit intact, as well as the isolation transformer for the
recorder output, with the recorder output transformer being driven (at the
center tap) by the output of the last DC amp stage of the null amp
circuit. That would maintain the isolation of the meter and recorder
output, and eliminate the need for an extra amp for them. It would also
maintain the guard integrity, keeping the instrument's operational
characteristics as close to original as possible.
By leaving the existing inverter circuit in place, you can easily derive
any voltages (+ and -) that your mod needs from it, without the need for
additional isolated power supplies
Dave M
Randy Evans wrote:
I finished the H-419A/Fluke 845A design modifications but I am still
trying to decide on the preferred power supply design. The basic
meter circuit uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V
batteries. The
basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
batteries should be able to go several thousand hours on a set of
batteries. For the meter circuit, it is always battery powered and
doesn't have to be plugged into the mains.
I also added a TI AMC1100 isolation amplifier for recording output
but it needs a 3.3 VDC isolated supply and a 5VDC output supply. The
current design uses separate isolation power supplies using LT8300
ICs that work off the mains transformer so there would be no worry
about failing batteries. Therefore, to use the recorder, the unit
would have to be plugged in. I am trying to decide if it would be
simpler to use batteries for the isolation circuit as well. If I use
batteries, do I use rechargeables or non-rechargeable batteries such
as the CR123s? The
circuit would need one set for the input isolated circuit side and
another set for the recorder output side and the batteries would not
last as long
as the meter circuit since the isolation circuits draw about 12
milliamps. They would still work about one hundred hours most likely
and would not
draw any current unless the isolation circuit is turned on (with a
separate toggle switch). My preference is to stay with the LT8300
power supplies
but I thought I would query the group.
Any thoughts on what would be your preferences?
Thanks,
Randy Evans
On Mon, Aug 4, 2014 at 8:33 AM, Randy Evans randyevans2688@gmail.com
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
I have used 845As and other instruments recorder output voltage to
digitize what I'm measuring. I'm surprised the 419A doesn't. I just
never looked before. So not like HP, I'm glad your considering adding
one.
On Mon, Dec 1, 2014 at 11:40 AM, Randy Evans <randyevans2688@gmail.com> wrote:
> Dave,
>
> The HP-419A is driving the need for an isolated recording output (it
> doesn't have one in the basic unit) and I wanted to provide one. The
> circuit is being designed to work with either the HP-419A or the Fluke
> 845A. The isolation circuit does not have to be used if not wanted since
> it is a completely separate circuit and not needed for the meter to work.
> I still need to work on the final HP-845A modifications and i will look at
> your suggestions.
>
> Randy
>
> On Sun, Nov 30, 2014 at 6:37 PM, Dave M <dgminala@mediacombb.net> wrote:
>
>> Randy,
>> Thanks for continuing with this modification.
>>
>> Speaking of the Fluke 845A;
>> At first glance, you could probably leave the existing power supply
>> inverter circuit intact, as well as the isolation transformer for the
>> recorder output, with the recorder output transformer being driven (at the
>> center tap) by the output of the last DC amp stage of the null amp
>> circuit. That would maintain the isolation of the meter and recorder
>> output, and eliminate the need for an extra amp for them. It would also
>> maintain the guard integrity, keeping the instrument's operational
>> characteristics as close to original as possible.
>> By leaving the existing inverter circuit in place, you can easily derive
>> any voltages (+ and -) that your mod needs from it, without the need for
>> additional isolated power supplies
>>
>> Dave M
>>
>>
>>
>> Randy Evans wrote:
>>
>>> I finished the H-419A/Fluke 845A design modifications but I am still
>>> trying to decide on the preferred power supply design. The basic
>>> meter circuit uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V
>>> batteries. The
>>> basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
>>> batteries should be able to go several thousand hours on a set of
>>> batteries. For the meter circuit, it is always battery powered and
>>> doesn't have to be plugged into the mains.
>>>
>>> I also added a TI AMC1100 isolation amplifier for recording output
>>> but it needs a 3.3 VDC isolated supply and a 5VDC output supply. The
>>> current design uses separate isolation power supplies using LT8300
>>> ICs that work off the mains transformer so there would be no worry
>>> about failing batteries. Therefore, to use the recorder, the unit
>>> would have to be plugged in. I am trying to decide if it would be
>>> simpler to use batteries for the isolation circuit as well. If I use
>>> batteries, do I use rechargeables or non-rechargeable batteries such
>>> as the CR123s? The
>>> circuit would need one set for the input isolated circuit side and
>>> another set for the recorder output side and the batteries would not
>>> last as long
>>> as the meter circuit since the isolation circuits draw about 12
>>> milliamps. They would still work about one hundred hours most likely
>>> and would not
>>> draw any current unless the isolation circuit is turned on (with a
>>> separate toggle switch). My preference is to stay with the LT8300
>>> power supplies
>>> but I thought I would query the group.
>>>
>>> Any thoughts on what would be your preferences?
>>>
>>> Thanks,
>>>
>>> Randy Evans
>>>
>>> On Mon, Aug 4, 2014 at 8:33 AM, Randy Evans <randyevans2688@gmail.com>
>>> 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
>>>>
>>>
>>
>> _______________________________________________
>> 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.
DM
Dave M
Mon, Dec 1, 2014 8:40 PM
I'll second that motion, Pete. Although I don't have a 419A anymore, the
mod should be a welcome feature. Although the 419A has a recorder output,
it isn't isolated, nor is the instrument guarded. At least, this mod will
isolate the recorder output circuit, which will be an improvement.
Dave M
Pete Lancashire wrote:
I have used 845As and other instruments recorder output voltage to
digitize what I'm measuring. I'm surprised the 419A doesn't. I just
never looked before. So not like HP, I'm glad your considering adding
one.
On Mon, Dec 1, 2014 at 11:40 AM, Randy Evans
randyevans2688@gmail.com wrote:
Dave,
The HP-419A is driving the need for an isolated recording output (it
doesn't have one in the basic unit) and I wanted to provide one.
The circuit is being designed to work with either the HP-419A or the
Fluke 845A. The isolation circuit does not have to be used if not
wanted since
it is a completely separate circuit and not needed for the meter to
work.
I still need to work on the final HP-845A modifications and i will
look at your suggestions.
Randy
On Sun, Nov 30, 2014 at 6:37 PM, Dave M dgminala@mediacombb.net
wrote:
Randy,
Thanks for continuing with this modification.
Speaking of the Fluke 845A;
At first glance, you could probably leave the existing power supply
inverter circuit intact, as well as the isolation transformer for
the recorder output, with the recorder output transformer being
driven (at the center tap) by the output of the last DC amp stage
of the null amp circuit. That would maintain the isolation of the
meter and recorder output, and eliminate the need for an extra amp
for them. It would also maintain the guard integrity, keeping the
instrument's operational characteristics as close to original as
possible.
By leaving the existing inverter circuit in place, you can easily
derive any voltages (+ and -) that your mod needs from it, without
the need for additional isolated power supplies
Dave M
Randy Evans wrote:
I finished the H-419A/Fluke 845A design modifications but I am
still trying to decide on the preferred power supply design. The
basic meter circuit uses the LTC2054 and LTC6255 with two CR123
Li-Ion 3 V batteries. The
basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
batteries should be able to go several thousand hours on a set of
batteries. For the meter circuit, it is always battery powered
and doesn't have to be plugged into the mains.
I also added a TI AMC1100 isolation amplifier for recording output
but it needs a 3.3 VDC isolated supply and a 5VDC output supply.
The current design uses separate isolation power supplies using
LT8300 ICs that work off the mains transformer so there would be
no worry about failing batteries. Therefore, to use the recorder,
the unit would have to be plugged in. I am trying to decide if it
would be simpler to use batteries for the isolation circuit as
well. If I use batteries, do I use rechargeables or
non-rechargeable batteries such as the CR123s? The
circuit would need one set for the input isolated circuit side and
another set for the recorder output side and the batteries would
not last as long
as the meter circuit since the isolation circuits draw about 12
milliamps. They would still work about one hundred hours most
likely and would not
draw any current unless the isolation circuit is turned on (with a
separate toggle switch). My preference is to stay with the LT8300
power supplies
but I thought I would query the group.
Any thoughts on what would be your preferences?
Thanks,
Randy Evans
On Mon, Aug 4, 2014 at 8:33 AM, Randy Evans
randyevans2688@gmail.com 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
I'll second that motion, Pete. Although I don't have a 419A anymore, the
mod should be a welcome feature. Although the 419A has a recorder output,
it isn't isolated, nor is the instrument guarded. At least, this mod will
isolate the recorder output circuit, which will be an improvement.
Dave M
Pete Lancashire wrote:
> I have used 845As and other instruments recorder output voltage to
> digitize what I'm measuring. I'm surprised the 419A doesn't. I just
> never looked before. So not like HP, I'm glad your considering adding
> one.
>
> On Mon, Dec 1, 2014 at 11:40 AM, Randy Evans
> <randyevans2688@gmail.com> wrote:
>> Dave,
>>
>> The HP-419A is driving the need for an isolated recording output (it
>> doesn't have one in the basic unit) and I wanted to provide one.
>> The circuit is being designed to work with either the HP-419A or the
>> Fluke 845A. The isolation circuit does not have to be used if not
>> wanted since
>> it is a completely separate circuit and not needed for the meter to
>> work.
>> I still need to work on the final HP-845A modifications and i will
>> look at your suggestions.
>>
>> Randy
>>
>> On Sun, Nov 30, 2014 at 6:37 PM, Dave M <dgminala@mediacombb.net>
>> wrote:
>>
>>> Randy,
>>> Thanks for continuing with this modification.
>>>
>>> Speaking of the Fluke 845A;
>>> At first glance, you could probably leave the existing power supply
>>> inverter circuit intact, as well as the isolation transformer for
>>> the recorder output, with the recorder output transformer being
>>> driven (at the center tap) by the output of the last DC amp stage
>>> of the null amp circuit. That would maintain the isolation of the
>>> meter and recorder output, and eliminate the need for an extra amp
>>> for them. It would also maintain the guard integrity, keeping the
>>> instrument's operational characteristics as close to original as
>>> possible.
>>> By leaving the existing inverter circuit in place, you can easily
>>> derive any voltages (+ and -) that your mod needs from it, without
>>> the need for additional isolated power supplies
>>>
>>> Dave M
>>>
>>>
>>>
>>> Randy Evans wrote:
>>>
>>>> I finished the H-419A/Fluke 845A design modifications but I am
>>>> still trying to decide on the preferred power supply design. The
>>>> basic meter circuit uses the LTC2054 and LTC6255 with two CR123
>>>> Li-Ion 3 V batteries. The
>>>> basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
>>>> batteries should be able to go several thousand hours on a set of
>>>> batteries. For the meter circuit, it is always battery powered
>>>> and doesn't have to be plugged into the mains.
>>>>
>>>> I also added a TI AMC1100 isolation amplifier for recording output
>>>> but it needs a 3.3 VDC isolated supply and a 5VDC output supply.
>>>> The current design uses separate isolation power supplies using
>>>> LT8300 ICs that work off the mains transformer so there would be
>>>> no worry about failing batteries. Therefore, to use the recorder,
>>>> the unit would have to be plugged in. I am trying to decide if it
>>>> would be simpler to use batteries for the isolation circuit as
>>>> well. If I use batteries, do I use rechargeables or
>>>> non-rechargeable batteries such as the CR123s? The
>>>> circuit would need one set for the input isolated circuit side and
>>>> another set for the recorder output side and the batteries would
>>>> not last as long
>>>> as the meter circuit since the isolation circuits draw about 12
>>>> milliamps. They would still work about one hundred hours most
>>>> likely and would not
>>>> draw any current unless the isolation circuit is turned on (with a
>>>> separate toggle switch). My preference is to stay with the LT8300
>>>> power supplies
>>>> but I thought I would query the group.
>>>>
>>>> Any thoughts on what would be your preferences?
>>>>
>>>> Thanks,
>>>>
>>>> Randy Evans
>>>>
>>>> On Mon, Aug 4, 2014 at 8:33 AM, Randy Evans
>>>> <randyevans2688@gmail.com> 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
DS
Dallas Smith
Tue, Dec 2, 2014 6:45 PM
Randy,
I'm glad to see that you completed your design, This could be the
ultimate permanent solution for these meters. My LED mod is still
working very well, but I think the zero of your design will solve
the offset drift problem. My led mod has a drift about ±100nv's over a
day or so, not perfect but better than the original specs. I changed the
value of C116 to 22uf tantalum, the response was a little to slow for
overloads. Your design may eliminate the need for the zero control
entirely.
Do the light pipes contribute to the high isolation resistance that the
Fluke 845 has? Will your modifications improve this spec? I may consider
your mod as a improved version, after your testing.
Since the mod, I was able to complete the self calibration of my Fluke
720 from beginning to end without the need to re-adjust the null meters
zero. This was the driving source for my mod,
Dallas
I finished the H-419A/Fluke 845A design modifications but I am still
trying to decide on the preferred power supply design. The basic
meter circuit uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V
batteries. The
basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
batteries should be able to go several thousand hours on a set of
batteries. For the meter circuit, it is always battery powered and
doesn't have to be plugged into the mains.
I also added a TI AMC1100 isolation amplifier for recording output
but it needs a 3.3 VDC isolated supply and a 5VDC output supply. The
current design uses separate isolation power supplies using LT8300
ICs that work off the mains transformer so there would be no worry
about failing batteries. Therefore, to use the recorder, the unit
would have to be plugged in. I am trying to decide if it would be
simpler to use batteries for the isolation circuit as well. If I use
batteries, do I use rechargeables or non-rechargeable batteries such
as the CR123s? The
circuit would need one set for the input isolated circuit side and
another set for the recorder output side and the batteries would not
last as long
as the meter circuit since the isolation circuits draw about 12
milliamps. They would still work about one hundred hours most likely
and would not
draw any current unless the isolation circuit is turned on (with a
separate toggle switch). My preference is to stay with the LT8300
power supplies
but I thought I would query the group.
Any thoughts on what would be your preferences?
Thanks,
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'm glad to see that you completed your design, This could be the
ultimate permanent solution for these meters. My LED mod is still
working very well, but I think the zero of your design will solve
the offset drift problem. My led mod has a drift about ±100nv's over a
day or so, not perfect but better than the original specs. I changed the
value of C116 to 22uf tantalum, the response was a little to slow for
overloads. Your design may eliminate the need for the zero control
entirely.
Do the light pipes contribute to the high isolation resistance that the
Fluke 845 has? Will your modifications improve this spec? I may consider
your mod as a improved version, after your testing.
Since the mod, I was able to complete the self calibration of my Fluke
720 from beginning to end without the need to re-adjust the null meters
zero. This was the driving source for my mod,
Dallas
> Randy Evans wrote:
>>> I finished the H-419A/Fluke 845A design modifications but I am still
>>> trying to decide on the preferred power supply design. The basic
>>> meter circuit uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V
>>> batteries. The
>>> basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
>>> batteries should be able to go several thousand hours on a set of
>>> batteries. For the meter circuit, it is always battery powered and
>>> doesn't have to be plugged into the mains.
>>>
>>> I also added a TI AMC1100 isolation amplifier for recording output
>>> but it needs a 3.3 VDC isolated supply and a 5VDC output supply. The
>>> current design uses separate isolation power supplies using LT8300
>>> ICs that work off the mains transformer so there would be no worry
>>> about failing batteries. Therefore, to use the recorder, the unit
>>> would have to be plugged in. I am trying to decide if it would be
>>> simpler to use batteries for the isolation circuit as well. If I use
>>> batteries, do I use rechargeables or non-rechargeable batteries such
>>> as the CR123s? The
>>> circuit would need one set for the input isolated circuit side and
>>> another set for the recorder output side and the batteries would not
>>> last as long
>>> as the meter circuit since the isolation circuits draw about 12
>>> milliamps. They would still work about one hundred hours most likely
>>> and would not
>>> draw any current unless the isolation circuit is turned on (with a
>>> separate toggle switch). My preference is to stay with the LT8300
>>> power supplies
>>> but I thought I would query the group.
>>>
>>> Any thoughts on what would be your preferences?
>>>
>>> Thanks,
>>>
>>>
>>> ______________________________________________
>>> 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
Wed, Dec 3, 2014 3:40 AM
The Fluke 845A is a very easy modification (in theory) since all that is
needed is a zero drift amp with a follow-up amp (need more gain to close
the loop with at least 40 dB margin). The LTC2054 and LTC6255 with two
voltage regulators to drop the +/-15V to +/- 2.5V for the op amps should be
all that is needed. Might want two 1.25V regulators for the zero offset to
minimize drift similar to what Dalla Smith did in his mod. I wanted to use
the LTC2054 since it has 1 pA bias current around room temp. Probably need
a PCB since IC sockets are a no-no to minimize thermals. The PCB would be
very simple but expensive since the cost at ExpressPCB is $66 for three
(with tax and shipping) the last time I ordered. I could probably fit at
least 6 circuits total on the three PCBs if anyone else is interested in
buying some of the PCBs for their mods.
Randy
On Tue, Dec 2, 2014 at 10:45 AM, Dallas Smith dosmith@outlook.com wrote:
Randy,
I'm glad to see that you completed your design, This could be the ultimate
permanent solution for these meters. My LED mod is still working very well,
but I think the zero of your design will solve the offset drift
problem. My led mod has a drift about ±100nv's over a day or so, not
perfect but better than the original specs. I changed the value of C116 to
22uf tantalum, the response was a little to slow for overloads. Your design
may eliminate the need for the zero control entirely.
Do the light pipes contribute to the high isolation resistance that the
Fluke 845 has? Will your modifications improve this spec? I may consider
your mod as a improved version, after your testing.
Since the mod, I was able to complete the self calibration of my Fluke 720
from beginning to end without the need to re-adjust the null meters zero.
This was the driving source for my mod,
Dallas
Randy Evans wrote:
I finished the H-419A/Fluke 845A design modifications but I am still
trying to decide on the preferred power supply design. The basic
meter circuit uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V
batteries. The
basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
batteries should be able to go several thousand hours on a set of
batteries. For the meter circuit, it is always battery powered and
doesn't have to be plugged into the mains.
I also added a TI AMC1100 isolation amplifier for recording output
but it needs a 3.3 VDC isolated supply and a 5VDC output supply. The
current design uses separate isolation power supplies using LT8300
ICs that work off the mains transformer so there would be no worry
about failing batteries. Therefore, to use the recorder, the unit
would have to be plugged in. I am trying to decide if it would be
simpler to use batteries for the isolation circuit as well. If I use
batteries, do I use rechargeables or non-rechargeable batteries such
as the CR123s? The
circuit would need one set for the input isolated circuit side and
another set for the recorder output side and the batteries would not
last as long
as the meter circuit since the isolation circuits draw about 12
milliamps. They would still work about one hundred hours most likely
and would not
draw any current unless the isolation circuit is turned on (with a
separate toggle switch). My preference is to stay with the LT8300
power supplies
but I thought I would query the group.
Any thoughts on what would be your preferences?
Thanks,
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.
The Fluke 845A is a very easy modification (in theory) since all that is
needed is a zero drift amp with a follow-up amp (need more gain to close
the loop with at least 40 dB margin). The LTC2054 and LTC6255 with two
voltage regulators to drop the +/-15V to +/- 2.5V for the op amps should be
all that is needed. Might want two 1.25V regulators for the zero offset to
minimize drift similar to what Dalla Smith did in his mod. I wanted to use
the LTC2054 since it has 1 pA bias current around room temp. Probably need
a PCB since IC sockets are a no-no to minimize thermals. The PCB would be
very simple but expensive since the cost at ExpressPCB is $66 for three
(with tax and shipping) the last time I ordered. I could probably fit at
least 6 circuits total on the three PCBs if anyone else is interested in
buying some of the PCBs for their mods.
Randy
On Tue, Dec 2, 2014 at 10:45 AM, Dallas Smith <dosmith@outlook.com> wrote:
> Randy,
>
> I'm glad to see that you completed your design, This could be the ultimate
> permanent solution for these meters. My LED mod is still working very well,
> but I think the zero of your design will solve the offset drift
> problem. My led mod has a drift about ±100nv's over a day or so, not
> perfect but better than the original specs. I changed the value of C116 to
> 22uf tantalum, the response was a little to slow for overloads. Your design
> may eliminate the need for the zero control entirely.
>
> Do the light pipes contribute to the high isolation resistance that the
> Fluke 845 has? Will your modifications improve this spec? I may consider
> your mod as a improved version, after your testing.
>
> Since the mod, I was able to complete the self calibration of my Fluke 720
> from beginning to end without the need to re-adjust the null meters zero.
> This was the driving source for my mod,
>
> Dallas
>
>
> Randy Evans wrote:
>>
>>> I finished the H-419A/Fluke 845A design modifications but I am still
>>>> trying to decide on the preferred power supply design. The basic
>>>> meter circuit uses the LTC2054 and LTC6255 with two CR123 Li-Ion 3 V
>>>> batteries. The
>>>> basic meter circuit draws less than 0.2 mA and with 1500 mAH CR123A
>>>> batteries should be able to go several thousand hours on a set of
>>>> batteries. For the meter circuit, it is always battery powered and
>>>> doesn't have to be plugged into the mains.
>>>>
>>>> I also added a TI AMC1100 isolation amplifier for recording output
>>>> but it needs a 3.3 VDC isolated supply and a 5VDC output supply. The
>>>> current design uses separate isolation power supplies using LT8300
>>>> ICs that work off the mains transformer so there would be no worry
>>>> about failing batteries. Therefore, to use the recorder, the unit
>>>> would have to be plugged in. I am trying to decide if it would be
>>>> simpler to use batteries for the isolation circuit as well. If I use
>>>> batteries, do I use rechargeables or non-rechargeable batteries such
>>>> as the CR123s? The
>>>> circuit would need one set for the input isolated circuit side and
>>>> another set for the recorder output side and the batteries would not
>>>> last as long
>>>> as the meter circuit since the isolation circuits draw about 12
>>>> milliamps. They would still work about one hundred hours most likely
>>>> and would not
>>>> draw any current unless the isolation circuit is turned on (with a
>>>> separate toggle switch). My preference is to stay with the LT8300
>>>> power supplies
>>>> but I thought I would query the group.
>>>>
>>>> Any thoughts on what would be your preferences?
>>>>
>>>> Thanks,
>>>>
>>>>
>>>> ______________________________________________
>>>> 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.
>
