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 <[email protected]> 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 <[email protected]> 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 <[email protected]> >>> 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 -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/volt-nuts >> and follow the instructions there. >> > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
