How do I Simulate an NTC Thermistor With Multisim?

The RESISTOR_VIRTUAL component includes temperature parameters such as TC1, TC2 and TNOM. Since I cannot set negative values for TC1 and TC2, how else can I make a simulated component in Multisim that behaves like a thermistor?

You can simulate NTCs in Multisim, but you cannot use the RESISTOR_VIRTUAL as a thermistor because it was designed to behave like an RTD. To simulate an NTC Thermistor you will need to :

1. Generate a new component with the component wizard (Tools>>Component Wizard)
2. If you have any concerns on how to use de Component Wizard, follow the suggestions in the Creating a Custom Component in NI Multisim tutorial.
3. Within the Select Simulation Model step, include a resistor model which reflects the thermistor's behavior. For example, you could include the following model for a 1 kΩ thermistor:

.SUBCKT 1KOHM_NTC__THERMISTORS__1__44 1 2 PARAMS: T0=20 R0=1k T1=120 R1=55
R1 1 2 (R0*((R1/R0)^((T0*T1-TEMP*T1)/(TEMP*T0-TEMP*T1))))
.ENDS 

Additional Information

How does an RTD resistor behave?
As temperature increases, its resistance rises according to:

How does an NTC thermistor behave?
As temperature increases, its resistance gets smaller according to the R vs. T equation:

If you want to derive the equation from known value pairs (T0,R0) and (T1,R1) instead of from the abstract values of K1 and b, the equation reads:

The model suggested in step 3 of the solution section uses this equation as part of the simuation model for a thermistor.