Re: [volt-nuts] HP-419 and Fluke 845 Modifications
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 dgmin...@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 randyevans2...@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.
Re: [volt-nuts] HP-419 and Fluke 845 Modifications
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 randyevans2...@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 dgmin...@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 randyevans2...@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. ___ 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: [volt-nuts] HP-419 and Fluke 845 Modifications
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 randyevans2...@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 dgmin...@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 randyevans2...@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.
