Page 299 - Mechatronics with Experiments

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ELECTRONIC COMPONENTS FOR MECHATRONIC SYSTEMS 285
AC supply line
AC outlet (grounded)
DC
Black power supply
White Hot
Green Neutral

+/– COM
Chassis
ground
Signal
ground
Sensor
(signal source)

–
+
Amplifier
A
(ground loop, if A - B connected,
B due to difference between two ground potentials)
Chasis Signal
ground ground
Earth ground
(i.e. of the building)
FIGURE 5.25: Grounding in an electrical circuit: earth ground, chassis ground, signal ground.

different kinds of grounds (Figure 5.25):
1. earth ground,
2. chassis ground,
3. signal (COMMON) ground.
Consider a single phase AC line in a residential building. The power plug to the supply line
has three leads: the hot wire (usually black color) which carries the AC power, the neutral
wire (usually white color) which is the reference, and the ground wire (usually green color)
which is physically connected to the earth via a large copper conductor. For instance, the
earth ground would be common to all outlets in a residential home, that is to say that all of
the ground wires from different outlets in the home would terminate at the same point for
the earth ground connection. Since earth is assumed to have infinite capacitance, as various
circuits dump current to it, its voltage potential does not change.
In general, chassis ground (grounding the metallic enclosure) is connected to the earth
ground as a safety measure. That way, if there is any voltage potential that may develop on
the chassis due to unintended electrical leakage, it would be “dumped” quickly to the earth,
hence not allowing a dangerous voltage level buildup on the chassis. Connecting the chassis
ground to the earth ground is an important safety measure in electrical devices (Figure 5.25,
see how the DC power supply connector connects the chasis ground to the earth ground
through the AC outlet). A device’s chassis is grounded only if it is connected to the earth
ground. For instance, in home appliance applications, sometimes there is only a two-prong