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6
2000
20k
200k
2000k
200
500
V~
OFF
SUNTEK
ST 1500
V---
500
200
2000
m
20
1.5v
mA 9v
200
mA ---
12 vac
2.3 ohms
50
25
500
250
500
100
50
Rx2000
Rx200
Rx20
Rx1
500ma
250ma
100ma
50ma
250
V/R
100
Com
Dcma
DCV
ACV
OHMS
DC AMPs
5
10
25
100
50
500
1000
2500
5000
500
250
100
250
100
50
20
10
5
50
100
20
10
5
50
20
10
5
25
12 vac
12 vac
V~
OFF
V---
mV---
A~
A---
V
300ma
10A
COM
FLUKE 21
12 vac
A
1.14 amps
Once you select the correct scale and type of value to be measured, it is
important to realize what the meter actually does when you take a measur-
ment. There is no magic involved but realizing what is actually taking place can
make the difference between accurately and safely diagnosing a reading and
obtaining misleading information.
Continuity / Resistance
These two terms are often confused because they are similar in nature. In
both cases the actual mechanics of the measurement are done by the meter
sending a voltage out over one lead and measuring the amount that is picked
up on the other lead. The meter selects the scale by dropping the voltage
through resistors (shunts) that are selected with the scales. Lower voltage will
be required to push through smaller resistance and still show a value in the
range of the display. (This is why you should never measure resistance or
continuity with the power on. It is very easy to exceed the circuit capabil-
ity, especially in 120/240 applications).
Continuity is a measurement of connection. Any voltage returning within a
certain range sounds a tone. Unfotunately, the operating range can be from
zero up to a hundred ohms or more and can give you misleading information.
This measurement is seldom usable for anything but detecting the presence of
connection.
Resistance is a measurement of the opposition to electron flow in a circuit.
The value is expressed in ohms and gives you the best representation of how
good a connection is between two points. When measuring to determine a
good connection always use the resistance scale to insure you can also diag-
nose the condition of the connection rather than just the presence of connec-
tion.
Voltage
When measuring voltage the meter is performing a comparison between
the potential on the two leads. In other words, it measures the distance of the
voltage on the red vs. the black lead. Understanding this is very important
as a zero reading does not necessarily mean there is no voltage pres-
ent. There can be 600 volts present in the circuit, but if it is felt on both leads
at the same time the display will show zero. Another condition that should be
watched for is when one of the points measured is not part of the circuit. An
open (loose wire, burned contacts, bad coil) circuit will not have any value to
the meter. There is a large difference between zero volts and no connection.
Once again, just because the meter reads zero, don't assume there is no
voltage present. It is always advisable to double check for the presence of
voltage before attempting to service any unit. By checking the ground (this is
one of the few times when using ground as a measuring point is advisable).
Current
The only time current is present is in a complete circuit. Therefore,
you cannot measure current outside the circuit like you can with voltage or
resistance. Unless you have an inductive coil (clamp on meter) it is neces-
sary for the current in the circuit to run through the meter to measure it.
The only way this can happen is to open the circuit and put the meter in
series with the current flow. Unfortunately, most meters can only handle
half an Amp (500ma) in this manner. Although some can handle up to 10
amps and/or have accessories that allow higher readings. Meters without
this capacity can be damaged by exceeding the capability of the current
monitoring circuit.
Meter Reading
Technical Services
