I tried that some time ago but, not surprisingly, the model didn't behave quite the same as the real thing in the lab. I concluded )to myself, only!) that chip self-heating and thermal coupling between the two devices was the stumbling block. Then after I sent the question to you yesterday, I did a bit of idle googling and came across this bbs.38hot.net/thread-105042-1-1.html (Not sure if the url pasted correctly...here are the salient bits
"Hello fellow forum users, I just finished with a telephone conversation with Bob Dobkin, and he was short on time, so I was not able to get all of the answers to every question I [and we] had, but here are the ones I was able to get: .... .... 5) They *could* make a model for LTspice, but the temperature effects are very difficult to simulate, and the market need is not large enough to support the development effort [my words]. He said the best way is to build the circuit and test it out in real life. ,,," Anyway, good job. I don't have a 732A, but am looking to get more than I paid for out of a 332B which happens to have had its RefAmp replaced with an LTFLU (before I got it). I am looking at your circuit now as food for a bit of improvement, perhaps... Roman -----Original Message----- From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of David C. Partridge Sent: Tuesday, 23 January 2018 10:03 PM To: 'Discussion of precise voltage measurement' Subject: Re: [volt-nuts] Redrafted schematic of Fluke 732A reference circuit It's nothing fancy just a glom of a 2n3904 and a 6.2V Zener wrapped up in .subckt/.ends and makes no claim to a an accurate model (I somehow doubt that either Fluke or LT would be willing to share that). ** LTFLU ** * * NI Multisim to SPICE Netlist Export * Generated by: amonra * Sat, Jan 20, 2018 15:16:41 * .SUBCKT LTFLU C B EK A *## Multisim Component LFLUD1 ##* xLFLUD1 A EK BZX84B6V2LT1/ON__ZENER__1 *## Multisim Component LFLUQ1 ##* qLFLUQ1 C B EK 2N3904__BJT_NPN__1 .SUBCKT BZX84B6V2LT1/ON__ZENER__1 2 1 ************************************** * Model Generated by MODPEX * *Copyright(c) Symmetry Design Systems* * All Rights Reserved * * UNPUBLISHED LICENSED SOFTWARE * * Contains Proprietary Information * * Which is The Property of * * SYMMETRY OR ITS LICENSORS * *Commercial Use or Resale Restricted * * by Symmetry License Agreement * ************************************** * Model generated on Dec 11, 03 * MODEL FORMAT: PSpice * anode cathode *node: 2 1 * Forward Section D1 2 1 MD1 .MODEL MD1 D IS=5.21532e-16 N=1 XTI=1 RS=0.5 + CJO=9.5e-11 TT=1e-08 * Leakage Current R 1 2 MDR 2e+07 .MODEL MDR RES TC1=0 TC2=0 * Breakdown IZG 4 2 0.12 R4 4 2 300 D3 2 4 MD3 .MODEL MD3 D IS=2.5e-12 N=0.37046 XTI=0 EG=0.1 D2 5 4 MD2 .MODEL MD2 D IS=2.5e-12 N=1.16158 XTI=0 EG=0.1 EV1 1 5 6 0 1 IBV 0 6 0.001 RBV 6 0 MDRBV 5792.79 .MODEL MDRBV RES TC1=0.000353198 *-- PSpice DIODE MODEL DEFAULT PARAMETER * VALUES ARE ASSUMED *IS=1E-14 RS=0 N=1 TT=0 CJO=0 *VJ=1 M=0.5 EG=1.11 XTI=3 FC=0.5 *KF=0 AF=1 BV=inf IBV=1e-3 TNOM=27 .ENDS bzx84b6v2lt1 .MODEL 2N3904__BJT_NPN__1 NPN(Is=6.734f Xti=3 Eg=1.11 Vaf=74.03 Bf=416.4 Ne=1.259 + Ise=6.734f Ikf=66.78m Xtb=1.5 Br=.7371 Nc=2 Isc=0 Ikr=0 Rc=1 + Cjc=3.638p Mjc=.3085 Vjc=.75 Fc=.5 Cje=4.493p Mje=.2593 Vje=.75 + Tr=239.5n Tf=301.2p Itf=.4 Vtf=4 Xtf=2 Rb=10) .ENDS LTFLU -----Original Message----- From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of romeo987 Sent: 23 January 2018 10:31 To: Discussion of precise voltage measurement Subject: Re: [volt-nuts] Redrafted schematic of Fluke 732A reference circuit David, Thank you for that - much easier to follow. I infer from this that you have a Spice model for the LTFLU. Can you elaborate, please? Roman > On 22 Jan 2018, at 2:15 pm, David C. Partridge > <david.partri...@perdrix.co.uk> wrote: > > OK folks here's another location for anyone who can't get it from eevblog.com: > > <http://www.perdrix.co.uk/manuals/Fluke%20732A%20Reference%20Circuit.p > df> > > Dave > > -----Original Message----- > From: volt-nuts > [mailto:volt-nuts-bounces+david.partridge=perdrix.co...@febo.com] On > Behalf Of m k > Sent: 21 January 2018 22:29 > To: Bob Albert; Discussion of precise voltage measurement > Subject: Re: [volt-nuts] Redrafted schematic of Fluke 732A reference > circuit > >> you possibly need to be logged into eevblog at the same time as you follow >> the link? > _______________________________________________ > 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. _______________________________________________ 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.