Simulating a variable resistance input with LTSpice?
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From: Joerg on 16 Apr 2010 15:42 Helmut Sennewald wrote: > "Joerg" <invalid(a)invalid.invalid> schrieb im Newsbeitrag > news:82rd6nFsp9U1(a)mid.individual.net... >> Jim Thompson wrote: >>> On Fri, 16 Apr 2010 06:03:50 -0700, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> neddie wrote: >>>>> On Apr 13, 7:58 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>>>> Hello Folks, >>>>>> >>>>>> Got stuck when trying to simulate an NTC. This temperature-variant >>>>>> resistor will be the only variable input so ".STEP" and stuff do not >>>>>> cut >>>>>> it because that only overlays multiple curve in an AC or DC >>>>>> simulation. >>>>>> I want just one curve: Output of my circuit versus varying NTC >>>>>> resistor >>>>>> value. >>>>>> >>>>>> Tried to make a voltage dependent resistor this way: >>>>>> >>>>>> http://www.electro-tech-online.com/attachments/general-electronics-ch... >>>>>> >>>>>> It works but is incredibly slow. Any better ideas? >>>>>> >>>>>> -- >>>>>> Regards, Joerg >>>>>> >>>>>> http://www.analogconsultants.com/ >>>>>> >>>>>> "gmail" domain blocked because of excessive spam. >>>>>> Use another domain or send PM. >>>>> .step temp 0 100 10 >>>>> , with simulation command set to DC op point >>>>> or am I missing something here. >>>>> Rob >>>> The it drew a staggered set of curves but I needed only one graph. >>> What exactly are you trying to do, Joerg? Get a DC output versus >>> temperature? Or what? You're showing less and less clarity as you go >>> :-) >>> >> Yes, a DC output versus temperature as _one_ contiguous graph. Not as a >> set of graphs like what the .step function usually does. >> >> But as I said, it's now all done and done, using a few sheets of paper and >> ye olde pencil :-) >> >> -- >> Regards, Joerg >> >> http://www.analogconsultants.com/ >> >> "gmail" domain blocked because of excessive spam. >> Use another domain or send PM. > > > Hello Joerg, > > If you use > > .step TEMP 0 100 1 > > together with only > > .OP > > You will get only one graph. > > There is one drawback with the global TEMP. > If you have opamp models around, they may suffer because of this varying > TEMP. > Opamp models are mostly made for only the standard temperature in SPICE > (27�C). > If this is the case with your circuit, I can make you another example where > the > NTC-resistor is controlled by a free variable, e.g. TMP. > Yes, there are opamps in there. But as I mentioned before I am already done with this circuit, did it in part with the old method (dead tree plus pencil, and lots of eraser crumbs by the end ...). But I still want to check out the file set you sent. Not sure if I can this weekend because I may have to work. Another switcher design. It almost feels like eating the same meal every day :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 17 Apr 2010 11:58 On Wed, 14 Apr 2010 10:14:33 -0700, qrk <SpamTrap(a)spam.net> wrote: [snip] > >********************************************************* >* NTC resistor using the Steinhart-Hart equation: * >* 1/T = A + B*ln(R) + C*ln(R)**3 (ugly solution for R) * >* Requires equation coefficients which can be * >* set in this subcircuit or passed thru the * >* X instantiation. e.g. * >* X1 1 0 THERMISTORntcS PARAMS: A=8.215E-4 B=2.111E-4 C=6.716E-8 * >* See Thermistor_Calculator.mcd for coefficient gen * >* Schematics component: RntcS * >* By: Mark 26 March 2003 * >********************************************************* >* +-------------------NTC resistor terminals >* | +------+------+- equation coeffs >coefficients >.SUBCKT THERMISTORntcS 1 2 PARAMS: A=8E-4 B=2E-4 C=7E-8 > .PARAM D={ ((1/(TEMP+273.15))-A)/(2*C) } > .PARAM E={ (B/(3*C))**3 } > .PARAM F={ SQRT(D**2+E) } > .PARAM G={ EXP(PWRS(D-F,1/3)+PWRS(D+F,1/3)) } > ETHERM 1 3 VALUE={ I(VSENSE)*G } > VSENSE 3 2 DC 0 >.ENDS THERMISTORntcS > > > >Regards, >Mark Hi Mark, Saturday morning, time to muse over adding your thermistor equation to my symbol and model libraries, and studying the Steinhart-Hart equations for "R", I wondered why you needed to use "PWRS"? They way I read those equations, "x" is always greater than "y/2", so simply PWR, or even **(1/3) should suffice. Or am I overlooking a trap (like, can B/3C be negative ?:-) Thanks! ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: qrk on 17 Apr 2010 13:31 On Sat, 17 Apr 2010 08:58:58 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Wed, 14 Apr 2010 10:14:33 -0700, qrk <SpamTrap(a)spam.net> wrote: > >[snip] >> >>********************************************************* >>* NTC resistor using the Steinhart-Hart equation: * >>* 1/T = A + B*ln(R) + C*ln(R)**3 (ugly solution for R) * >>* Requires equation coefficients which can be * >>* set in this subcircuit or passed thru the * >>* X instantiation. e.g. * >>* X1 1 0 THERMISTORntcS PARAMS: A=8.215E-4 B=2.111E-4 C=6.716E-8 * >>* See Thermistor_Calculator.mcd for coefficient gen * >>* Schematics component: RntcS * >>* By: Mark 26 March 2003 * >>********************************************************* >>* +-------------------NTC resistor terminals >>* | +------+------+- equation coeffs >>coefficients >>.SUBCKT THERMISTORntcS 1 2 PARAMS: A=8E-4 B=2E-4 C=7E-8 >> .PARAM D={ ((1/(TEMP+273.15))-A)/(2*C) } >> .PARAM E={ (B/(3*C))**3 } >> .PARAM F={ SQRT(D**2+E) } >> .PARAM G={ EXP(PWRS(D-F,1/3)+PWRS(D+F,1/3)) } >> ETHERM 1 3 VALUE={ I(VSENSE)*G } >> VSENSE 3 2 DC 0 >>.ENDS THERMISTORntcS >> >> >> >>Regards, >>Mark > >Hi Mark, > >Saturday morning, time to muse over adding your thermistor equation to >my symbol and model libraries, and studying the Steinhart-Hart >equations for "R", I wondered why you needed to use "PWRS"? > >They way I read those equations, "x" is always greater than "y/2", so >simply PWR, or even **(1/3) should suffice. > >Or am I overlooking a trap (like, can B/3C be negative ?:-) > >Thanks! > > ...Jim Thompson Not sure why I used PWRS. This was done 7 years ago and my stack overfloweth. I would guess that it's force of habit or there could be a negative value involved. I sort of remember fighting with the PWR function and realizing that it didn't honor the negative sign some years ago. Mark
From: Jim Thompson on 17 Apr 2010 13:42 On Sat, 17 Apr 2010 08:58:58 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Wed, 14 Apr 2010 10:14:33 -0700, qrk <SpamTrap(a)spam.net> wrote: > >[snip] >> >>********************************************************* >>* NTC resistor using the Steinhart-Hart equation: * >>* 1/T = A + B*ln(R) + C*ln(R)**3 (ugly solution for R) * >>* Requires equation coefficients which can be * >>* set in this subcircuit or passed thru the * >>* X instantiation. e.g. * >>* X1 1 0 THERMISTORntcS PARAMS: A=8.215E-4 B=2.111E-4 C=6.716E-8 * >>* See Thermistor_Calculator.mcd for coefficient gen * >>* Schematics component: RntcS * >>* By: Mark 26 March 2003 * >>********************************************************* >>* +-------------------NTC resistor terminals >>* | +------+------+- equation coeffs >>coefficients >>.SUBCKT THERMISTORntcS 1 2 PARAMS: A=8E-4 B=2E-4 C=7E-8 >> .PARAM D={ ((1/(TEMP+273.15))-A)/(2*C) } >> .PARAM E={ (B/(3*C))**3 } >> .PARAM F={ SQRT(D**2+E) } >> .PARAM G={ EXP(PWRS(D-F,1/3)+PWRS(D+F,1/3)) } >> ETHERM 1 3 VALUE={ I(VSENSE)*G } >> VSENSE 3 2 DC 0 >>.ENDS THERMISTORntcS >> >> >> >>Regards, >>Mark > >Hi Mark, > >Saturday morning, time to muse over adding your thermistor equation to >my symbol and model libraries, and studying the Steinhart-Hart >equations for "R", I wondered why you needed to use "PWRS"? > >They way I read those equations, "x" is always greater than "y/2", so >simply PWR, or even **(1/3) should suffice. > >Or am I overlooking a trap (like, can B/3C be negative ?:-) > >Thanks! > > ...Jim Thompson And it looks like "standard" data is resistance versus temperature tables, rather than specifying A, B & C. Is that typical, or am I not looking in the right places? It _would_ be easy enough to specify the subcircuit with parameter pairs, R1/T1, R2/T2, R3/T3, then have the behavioral model compute A, B & C. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: Joerg on 17 Apr 2010 15:38
Jim Thompson wrote: > On Sat, 17 Apr 2010 08:58:58 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >> On Wed, 14 Apr 2010 10:14:33 -0700, qrk <SpamTrap(a)spam.net> wrote: >> >> [snip] >>> ********************************************************* >>> * NTC resistor using the Steinhart-Hart equation: * >>> * 1/T = A + B*ln(R) + C*ln(R)**3 (ugly solution for R) * >>> * Requires equation coefficients which can be * >>> * set in this subcircuit or passed thru the * >>> * X instantiation. e.g. * >>> * X1 1 0 THERMISTORntcS PARAMS: A=8.215E-4 B=2.111E-4 C=6.716E-8 * >>> * See Thermistor_Calculator.mcd for coefficient gen * >>> * Schematics component: RntcS * >>> * By: Mark 26 March 2003 * >>> ********************************************************* >>> * +-------------------NTC resistor terminals >>> * | +------+------+- equation coeffs >>> coefficients >>> .SUBCKT THERMISTORntcS 1 2 PARAMS: A=8E-4 B=2E-4 C=7E-8 >>> .PARAM D={ ((1/(TEMP+273.15))-A)/(2*C) } >>> .PARAM E={ (B/(3*C))**3 } >>> .PARAM F={ SQRT(D**2+E) } >>> .PARAM G={ EXP(PWRS(D-F,1/3)+PWRS(D+F,1/3)) } >>> ETHERM 1 3 VALUE={ I(VSENSE)*G } >>> VSENSE 3 2 DC 0 >>> .ENDS THERMISTORntcS >>> >>> >>> >>> Regards, >>> Mark >> Hi Mark, >> >> Saturday morning, time to muse over adding your thermistor equation to >> my symbol and model libraries, and studying the Steinhart-Hart >> equations for "R", I wondered why you needed to use "PWRS"? >> >> They way I read those equations, "x" is always greater than "y/2", so >> simply PWR, or even **(1/3) should suffice. >> >> Or am I overlooking a trap (like, can B/3C be negative ?:-) >> >> Thanks! >> >> ...Jim Thompson > > And it looks like "standard" data is resistance versus temperature > tables, rather than specifying A, B & C. Is that typical, or am I not > looking in the right places? > That is the standard for NTC. Probably because the big market for them is industrial control and the usual PLC can't do much more than simple ladder logic. Also, those things have large tolerances so there ain't no real precision. However, if you run a tight PID control with them the table surely doesn't cut it. > It _would_ be easy enough to specify the subcircuit with parameter > pairs, R1/T1, R2/T2, R3/T3, then have the behavioral model compute A, > B & C. > Most of the times when I try this the PC starts to bog down. And heat the office which is nice these days but not in August :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |