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 connections only so that 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 wires only, 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 to be correct during a brief electrical test.
Testing diodes, LEDs With the right tester you can check a diode for presence and polarity. Zener diodes may also be tested for reverse breakdown voltage. LEDs 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, LEDs 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)
  1. Replace the wire (pins 1 and 2) with a 100-ohm resistor. The test should fail (this simulates a "high resistance" connection).
  2. Short a 100 ohm resistor (short pins 3 and 4). The test should fail.
  3. Add a 100 ohm resistor between pins 3 and 5. The test should fail.
  4. 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 ensure no damage to components during hipot testing by closely checking the test program to make sure all components are included.