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Standard Testing
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Guidelines for Testing Components |
Guidelines for Testing Components
| Test
Situation |
Considerations |
| Test coverage with simple continuity (pattern
only) testers |
Continuity testers check only the pattern of
connections. These testers treat passive components (resistors,
diodes, capacitors) as just connections so common errors can be
missed when passive components are present. For example, if the
resistance is low enough, a resistor will look like a
connection/wire. A short across this resistor will not be
detected during the test. Continuity
testers (Cirris 1000M, 2000, LC) work well for assemblies that
contain only wires but we recommend you use a more advanced
connection resistance tester (1000R+, 1100H+, Touch1, CR, CH+)
when your assemblies contain components. |
| Testing resistors |
With the right tester you can easily verify a
resistor's value. However, when there are other resistors in
parallel with the resistor being tested, the measured value will
be lower as defined by the formula Rmeasured = R1*R2/(R1+R2).
If the tester self-learns the assembly you'll
notice the resistance values automatically account for the
parallel effects. If you are creating a test program, you will
need to adjust the resistance values for the parallel effects.
MDA testers may use point guarding to eliminate the effects of
parallel components. |
| Testing capacitors |
With the right tester you can verify a
capacitor's value. However, the fixturing's capacitance will add
to the value of the capacitor being measured. When the capacitor
values are small you will need to adjust the capacitance
instructions to include the fixturing capacitance.
When a capacitor is in parallel with a resistor,
the measured value may be affected. The Cirris 1000H+, 1100H+,
CH+, and Touch 1 are designed to cancel these effects when the
time constant (RxC) is >1ms. (For example a 100Ω resistor in
parallel with a 10µf capacitor). |
| Testing electrolytic and tantalum capacitor
polarity |
Detecting reverse polarity of electrolytic
and tantalum capacitors usually requires visual inspection since
the capacitance value will appear correct during a brief
electrical test. |
| Testing diodes, LED's |
With the right tester you can check a diode
for presence and polarity. Zener diodes may also be tested for
reverse breakdown voltage. LED's can be checked with voltage
drop for proper color and may also be turned on for visual
inspection. |
| Testing more than just capacitors, diodes,
and resistors |
When a tester self-learns it might not
identify all the components in the assembly. Many testers allow
you to add instructions to test various components. You can
check the resistance of inductors, thermocouples, MOV's (Metal
Oxide Varistors), switches, relays, proximity switches, high
voltage zener diodes, "Transorbs", serial EEPROM's (including
programming), transistors, orientation of IC's and open pins to
IC's, opto-couplers, LED's and more. It can be a challange to
verify certain components using resistance, capacitance, or
voltage-drop measurements. Let us know about your applications
and we'll help you come up with an appropriate testing solution. |
| Verifying component accuracy |
Consider having test equipment that is at
least four times more accurate than the components you are
testing and you will reduce the chance of rejecting components
that are really within specification.
Lower accuracy testers can be used to detect the common error of
a "wrong-value component" being used. Since the jump from one
standard component value to the next is generally 10%, a less
accurate tester is still effective at finding "wrong-value
components." |
| Testing twisted-pairs |
To check twisted-pair cabling, continuity
testing alone is not sufficient. It is possible to have proper
point-to-point continuity and still have split-pairs. A tester
with sensitive capacitance measurement capability can detect
split-pairs. If your application also requires near-end/far-end
crosstalk and attenuation tests you'll need to select a tester
with those capabilities. |
| Catching shorts with dual-threshold tests |
Some testers that claim to test for resistors
and other components still allow serious errors to escape. Check
to see if your tester can catch the following defects. Build
this sample circuit, program your tester for this circuit, and
perform the following tests.
- One wire (pin 1 to pin 2)
- Two 100 ohm resistors (one from pin 3 to
pin 4 and one from pin 5 to pin 6)
- Two diodes pointing toward each other
(both cathodes [striped ends] to pin 8, one anode to pin 7,
the other anode to pin 9)
- Replace the wire (pins 1 and 2) with a
100-ohm resistor. The test should fail (this simulates a
"high resistance" connection).
- Short a 100 ohm resistor (short pins 3
and 4). The test should fail.
- Add a 100-ohm resistor between pins 3 and
5. The test should fail.
- Create a short between the diodes (short
pin 7 to pin 9). The test should fail.
Advanced Cirris testers (Touch1, 1000R+/H+,
1100 R+/H+, easy-wire CR/CH) use a dual-threshold test. One
threshold to detect shorts within networks of components and a
separate, higher threshold to detect shorts between wires. This
approach gives the most effective fault coverage. These testers
self-learn this type of assembly and provide an effective test
for it. |
| Components effect on test speed |
Assemblies with wires only (no components)
are tested very quickly (hundreds of points per second).
Assemblies with lots of passive components, especially if these
components have many common connections, slow down the test rate
dramatically. With slower testing it gets harder to find
intermittent errors. |
| Damage to components with low voltage tests |
Low voltage tests need to be current limited
to prevent damage to sensitive components such as ICs. Although
a test is described as operating at 5 volts or 10 volts, maximum
power is kept low because the measurement current is properly
limited and voltage generally doesn't reach even 1 volt. (For
Cirris testers that measure resistance, this is a very safe 0.1
watt for less than 0.002 seconds. Cirris testers performing
4-wire Kelvin tests are limited to a much larger 1.6 watts for
up to 0.02 seconds which could damage sensitive components.)
|
| Damage to components with high voltage tests |
Hipot testing verifies proper electrical
isolation between circuits. It is safe to perform hipot tests on
assemblies with embedded components as long as no voltage drop
occurs across any component. It is okay for both ends of a
component to be raised to a high voltage with respect to other
points in an assembly. Many testers self-learn the test program
and might not properly learn all components. You can assure no
damage to components during hipot testing by closely checking
the test program to make sure all components are included. |
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