# LTspice help

Discussion in 'The Projects Forum' started by sunil_r_sp, Feb 18, 2007.

1. ### sunil_r_sp Thread Starter Member

Feb 18, 2007
13
0
me workin on my project in LTspice.....is there any method to find the resistance between 2 nodes directly in LTspice....

2. ### Papabravo Expert

Feb 24, 2006
10,163
1,796
It may not be easy or straightforward but you can write an expression for the voltage difference between two nodes divided by the sum of the currents in each branch. Why you would want to do this is quite beyond me and seems excessively error prone.

3. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
That's basically the right idea, but there's an easier way.
In an AC simulation, all components are linearized at the DC operating point. You can apply a 1 amp AC current source between the two nodes at any frequency (or use a frequency sweep), and then measure the voltage across the current source. If you have no other active AC sources in your simulation, then Z=V/I, and I=1, so Z=V (numerically).
To measure the voltage between two nodes, place the probe on one node, then, while holding down the left mouse button, drag the probe to the other node and release the button.
It may seem ridiculous to apply an amp across 2 nodes, but it works because the simulator linearizes all components at the operating point. You could apply a microamp or a thousand amps and get the same answer.