In this case, with the full-scale output 50 mV at F = 500, the SENS = 50mV/(10V*500) = 10e-6.įigure 6: Simulation result for Strain Gauge Bridge circuitįigure 1: Top-level schematic for the frequency comparator circuit Within the normal operating range, the bridge output is 10V*(F*SENS).
R can be determined by the gauge’s current drain (I) at the bias voltage (V), that is, R = V/I. SENS sets the sensitivity of the gauge and F is the applied force.įor example, as strain gauge is part of a pressure sensor, the full-scale output is 50 mV with a bias voltage of 10 V and the full scale corresponds to a pressure of 500 psi. SUBCKT POT (TOP, BOTTOM, TAP) PARAMS: R=1K RANGE=1000 SET=.5 The potentiometer can then be implemented by the following subcircuit. So far we have assumed that the pot is linear, but for a logarithmic pot we need an extra parameter, that is, the dynamic range of the pot. Note: The pot R1 is swept to show the adjustment range of the regulator.įigure 1: Linear potentiometer test circuitįigure 2: Simulation result for Linear potentiometer circuitįor this analysis, a DC sweep of the parameter PSET is used and PSET is swept from 0 to 1 in increments of 0.2. The following example circuit shows that how a pot may be used with an adjustable regulator. In schematics there is a symbol for a potentiometer located in breakout.olb. Here a 10k pot is used in 6 runs, having the settings 0.
In other words, there is no loss of information by running several transient analyses and varying the pot’s setting with a. This is appropriate for almost all applications, since the time required for the movement of the pot is much longer than the electrical time constants of the circuit. So far, the setting of the pot has been static. 001 (instead of 0) are used to prevent the resistors from having 0 ohms at the extremes. SUBCKT POT 1 T 2 PARAMS: VALUE=1K SET=0.5 That is, where the center tap is set.Ī convenient way to describe this is to define SET to be 0 when the tap is all the way at the bottom and 1 when it is all the way at the top.Ī potentiometer can be implemented by the following subcircuit: The specification for the potentiometer consists of:Ģ. The model suggested in step 3 of the solution section uses this equation as part of the simuation model for a thermistor.In this application note, we will model potentiometers and variable resistors using OrCAD Capture and simulate the example circuits, which include models of potientiometer and variable resistors, using PSpice.Įlectrically, a potentiometer consists of two resistors connected in series. 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: R1 1 2 (R0*((R1/R0)^((T0*T1-TEMP*T1)/(TEMP*T0-TEMP*T1))))Īdditional Information How does an RTD resistor behave?Īs temperature increases, its resistance rises according to:Īs temperature increases, its resistance gets smaller according to the R vs. For example, you could include the following model for a 1 kΩ thermistor: Within the Select Simulation Model step, include a resistor model which reflects the thermistor's behavior.
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.Generate a new component with the component wizard ( Tools>Component Wizard).To simulate an NTC Thermistor you will need to :
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.