# help with circuit sim

Discussion in 'General Electronics Chat' started by kingArgon, Mar 14, 2012.

1. ### kingArgon Thread Starter Member

Mar 20, 2011
33
1
Maybe this is something for the LTSpice forum but it has been happening in every circuit sim i use. I am trying to simulate the circuit in one of the tutorials. Specifically http://www.allaboutcircuits.com/vol_1/chpt_5/2.html.
the resistances are 3k,5k, 10k and the voltage is 9volts. in the sim the voltage drop across the 3k resistor is 7.5v and across the 5k its 2.4999 volts. which would mean i gained a volt. can someone help me?

2. ### MrChips Moderator

Oct 2, 2009
18,330
5,793
You are obviously measuring your voltages incorrectly.

The current is 0.5mA

The voltage across 3k is 1.5V
The voltage across 10k is 5.0V
The voltage across 5k is 2.5V

What you are measuring is the voltage at the junctions 2 and 3 with respect to junction 4.

You are confusing the terms "voltage at" and "voltage across".
Voltages are always measured with respect to something. It is always a voltage difference or a "voltage drop" or "voltage across".

3. ### Ron H AAC Fanatic!

Apr 14, 2005
7,012
681
To measure the voltage from one node to another, put the probe on one of the nodes, then left click and hold while you drag the probe (it will turn black) to the other node, then release. The voltage on the first node will be relative to the voltage on the second node.

4. ### kingArgon Thread Starter Member

Mar 20, 2011
33
1
thankyoou Mr.Chips and Ron for the quick response.

Ron that was the issue, i was just measuring wrong. its working now! )