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Guardian Technologies 5209 User Manual

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section 2
MeasuRing electRicitY

Component testing may require a specific resis-

tance value or a test for INFINITY or CONTINUITY.

Infinity is an OPEN condition between two electrical

points, which would read as no resistance on a VOM.

Continuity is a CLOSED condition between two elec-

trical points, which would be indicated as very low

resistance or “ZERO” on a VOM.

ELECTRICAL UNITS

AMPERE:
The rate of electron flow in a circuit is represented

by the AMPERE. The ampere is the number of elec-

trons flowing past a given point at a given time. One

AMPERE is equal to just slightly more than six thou-

sand million billion electrons per second (6.25 x 10

18

).

With alternating current (AC), the electrons flow first

in one direction, then reverse and move in the oppo-

site direction. They will repeat this cycle at regular

intervals. A wave diagram, called a “sine wave” shows

that current goes from zero to maximum positive

value, then reverses and goes from zero to maximum

negative value. Two reversals of current flow is called

a cycle. The number of cycles per second is called

frequency and is usually stated in “Hertz”.

VOLT:
The VOLT is the unit used to measure electrical

PRESSURE, or the difference in electrical potential

that causes electrons to flow. Very few electrons will

flow when voltage is weak. More electrons will flow as

voltage becomes stronger. VOLTAGE may be consid-

ered to be a state of unbalance and current flow as

an attempt to regain balance. One volt is the amount

of EMF that will cause a current of 1 ampere to flow

through 1 ohm of resistance.

-

+

aMpeRe - Unit measuring rate of

current flow (number of electrons
past a given point)

oHM - Unit measuring resistance

or opposition to flow

volt - Unit measuring force or

difference in potential
causing current flow

Conductor of a
Circuit

Figure 2-5. – Electrical Units

OHM:
The OHM is the unit of RESISTANCE. In every circuit

there is a natural resistance or opposition to the flow

of electrons. When an EMF is applied to a complete

circuit, the electrons are forced to flow in a single

direction rather than their free or orbiting pattern. The

resistance of a conductor depends on (a) its physical

makeup, (b) its cross-sectional area, (c) its length,

and (d) its temperature. As the conductor's tempera-

ture increases, its resistance increases in direct pro-

portion. One (1) ohm of resistance will permit one (1)

ampere of current to flow when one (1) volt of electro-

motive force (EMF) is applied.

OHM'S LAW

A definite and exact relationship exists between

VOLTS, OHMS and AMPERES. The value of one can

be calculated when the value of the other two are

known. Ohm's Law states that in any circuit the current

will increase when voltage increases but resistance

remains the same, and current will decrease when

resistance Increases and voltage remains the same.

VOLTS

(E)

AMPS

(I)

OHMS

(R)

Figure 2-6. – Ohm's Law

If AMPERES is unknown while VOLTS and OHMS are

known, use the following formula:

AMPERES = VOLTS

OHMS

If VOLTS is unknown while AMPERES and OHMS are

known, use the following formula:

VOLTS = AMPERES x OHMS

If OHMS is unknown but VOLTS and AMPERES are

known, use the following:

OHMS = VOLTS

AMPERES

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