Programming instructions

 National Instruments Corporation 1-1 Multisim Component Reference Guide
Chapter 1
Source Components
1.1 Ground
A voltage measurement is always referenced to some point, since a voltage is actually a
“potential difference” between two points in a circuit.
The concept of “ground” is a way of defining a point common to all voltages. It represents 0
volts. All voltage levels around the circuit are positive or negative when compared to ground.
In power systems, the planet Earth itself is used for this reference point (most home power
circuits are ultimately “grounded” to the Earth's surface for lightning protection). This is how
the expression “earthing” or “grounding” a circuit originated.
Most modern power supplies have “floating” positive and negative outputs, and either output
point can be defined as ground. These types of supplies can be used as positive (with respect
to ground) or negative power supplies. In floating power supply circuits, the positive output is
often used as the voltage reference for all parts of the circuit.
Note Multisim supports a multipoint grounding system. Each ground connected is made
directly to the ground plane.
The Ground Component
This component has 0 voltage and so provides a clear reference point for calculating electrical
values. You can use as many ground components as you want. All terminals connected to
ground components represent a common point and are treated as joined together.
Not all circuits require grounding for simulation; however, any circuit that uses an opamp,
transformer, controlled source or oscilloscope must be grounded. Also, any circuit which
contains both analog and digital components should be grounded. If a circuit is ungrounded or
improperly grounded (even if it does not need grounding in reality), it may not be simulated.
If it is simulated, it may produce inconsistent results. The linear transformer must be
grounded on both sides.
ComponentRef.book Page 1 Thursday, December 7, 2006 10:12 AM