Simulating a variable resistance input with LTSpice?
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From: Jim Thompson on 14 Apr 2010 10:53 On Tue, 13 Apr 2010 20:42:58 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: >> On Tue, 13 Apr 2010 10:58:03 -0700, Joerg <invalid(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-chat/40714d1269571000-sine-variable-resistor-ltspice-d2.png >>> >>> It works but is incredibly slow. Any better ideas? >> >> Thompson's Fundamental Rule #1, Stay away from PhD's, use this >> instead.... >> >> http://www.efunda.com/designstandards/sensors/thermistors/thermistors_theory.cfm >> > >That ain't the normal thermistor curve. There are some switching types >where there's reversal but those are typically used sans controller, as >triggers, before something goes kablouie. > > >> Do you really have one bad enough to need the high order corrections? >> > >The client asked that they'd like to see at least 12 bits so I figure >they have a reason for that. In the late '60's I had customers ask me for 16-bit audio for the sound system of an L1011... asking doesn't make them have a legitimate reason :-) ...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 14 Apr 2010 11:22 Jim Thompson wrote: > On Tue, 13 Apr 2010 20:42:58 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Tue, 13 Apr 2010 10:58:03 -0700, Joerg <invalid(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-chat/40714d1269571000-sine-variable-resistor-ltspice-d2.png >>>> >>>> It works but is incredibly slow. Any better ideas? >>> Thompson's Fundamental Rule #1, Stay away from PhD's, use this >>> instead.... >>> >>> http://www.efunda.com/designstandards/sensors/thermistors/thermistors_theory.cfm >>> >> That ain't the normal thermistor curve. There are some switching types >> where there's reversal but those are typically used sans controller, as >> triggers, before something goes kablouie. >> >> >>> Do you really have one bad enough to need the high order corrections? >>> >> The client asked that they'd like to see at least 12 bits so I figure >> they have a reason for that. > > In the late '60's I had customers ask me for 16-bit audio for the > sound system of an L1011... asking doesn't make them have a legitimate > reason :-) > That was one fine aircraft. The best flight on one was with Air Caledonian from London to Shannon. With a grand total of about 20 passengers in there ... Projects are sorta piling up here, this afternoon a new one in the aerospace field will be discussed. Why is it that you chip guys complain about a dry market inside the US and us hardware guys are living under a chunk of domestic projects? -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 14 Apr 2010 11:56 On Wed, 14 Apr 2010 08:22:45 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Jim Thompson wrote: [snip] >> >> In the late '60's I had customers ask me for 16-bit audio for the >> sound system of an L1011... asking doesn't make them have a legitimate >> reason :-) >> > >That was one fine aircraft. I agree. And it was back in the days where stewardesses were pretty and had pleasant personalities :-) >The best flight on one was with Air >Caledonian from London to Shannon. With a grand total of about 20 >passengers in there ... > >Projects are sorta piling up here, this afternoon a new one in the >aerospace field will be discussed. Why is it that you chip guys complain >about a dry market inside the US and us hardware guys are living under a >chunk of domestic projects? I don't know. I'm finally starting to see inquiries from within the US, but they're coming via my SE Asia connections. Of course, manufacturing is to be done in mainland China :-) ...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 14 Apr 2010 12:30 Jim Thompson wrote: > On Wed, 14 Apr 2010 08:22:45 -0700, Joerg <invalid(a)invalid.invalid> > wrote: [...] >> Projects are sorta piling up here, this afternoon a new one in the >> aerospace field will be discussed. Why is it that you chip guys complain >> about a dry market inside the US and us hardware guys are living under a >> chunk of domestic projects? > > I don't know. I'm finally starting to see inquiries from within the > US, but they're coming via my SE Asia connections. Of course, > manufacturing is to be done in mainland China :-) > For my consumer market designs that's sometimes also the case. But aerospace and similar high-end products like that are made right here in our country. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: qrk on 14 Apr 2010 13:14
On Tue, 13 Apr 2010 10:58:03 -0700, Joerg <invalid(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-chat/40714d1269571000-sine-variable-resistor-ltspice-d2.png > >It works but is incredibly slow. Any better ideas? Here's a couple NTC subcircuits I made up for PSpice. LTspice is compatible with PSpice syntax, so these should work. These respond to the temperature parameter in Spice. Easiest to use the Beta equation approximation, but Steinhart-Hart equation is a bit more accurate. ************************************************** * NTC resistor using the Beta equation: * * R = Ro * EXP(B*(1/T - 1/298.15)) * * Requires resistor value at 25 deg C and Beta * * which can be set in this subcircuit or passed * * thru the X instantiation. e.g. * * X1 1 0 THERMISTORntcB PARAMS: Ro=100k B=4300 * * Schematics component: RntcB * * By: Mark 26 March 2003 * ************************************************** * +------------------- NTC resistor terminals * | * | +-------- Resistance at 25 deg C * | | +- Beta value ..SUBCKT THERMISTORntcB 1 2 PARAMS: Ro=10k B=4300 ETHERM 1 3 VALUE={ I(VSENSE)*Ro*EXP(B*(1/(TEMP+273.15)-1/298.15)) } VSENSE 3 2 DC 0 ..ENDS THERMISTORntcB ********************************************************* * 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 |