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Number 2208
Application Note Solutions for Production Testing
Series of Connectors
Introduction become shorted tomorrow in an environment with high heat and
vibration, such as under the hood of a car.
As electronics have become increasingly pervasive, the
Isolation is typically tested by applying a voltage across
importance of electrical connectors has also increased dramatic-
two pins in a connector and measuring the resulting current that
ally. Quality connectors are vital to ensuring overall product
flows between them. The corresponding resistance from the test
reliability in applications ranging from motor vehicles to trans-
is compared to a predetermined threshold value. If the resistance
atlantic telecom systems. This application note addresses many
level is too low, the connector is rejected. Common threshold
of the issues involved in implementing a connector characteriza-
levels range from 1M to 1T. The isolation resistance is
tion system.
shown as Riso in Figure 1.
The degree and type of electrical testing that connectors
When testing very high ohmic devices, the measured
undergo typically depends on how crucial they are to the overall
resistance may change significantly in response to a change in
performance of the systems in which they're installed. Stringent
the applied voltage, an effect known as the voltage coefficient of
electrical tests are often specified when high reliability is
resistance. This effect makes it preferable to test high value
required. Obviously, connectors used in international telecommu-
resistors with the constant voltage, measure current method. The
nications systems are more crucial than the serial port connector
actual test voltage chosen depends on the capabilities of the
on the back of a desktop personal computer.
instrumentation and the degree of current measurement sensitivi-
The two most commonly measured parameters in connec- ty available. For a given resistance value, a higher voltage will
tor testing are isolation and continuity. Isolation measurements result in a higher current signal, which can be measured with
are usually performed between each of the connector pins or higher resolution. Figure 2 illustrates the constant voltage
between the pins and the outer shell of the connector. Also, method for measuring high resistances.
during connector manufacturing and testing (both mechanical
and environmental testing), the continuity may become
compromised. Testing the continuity of each pin ensures that RIsolation
once the connector is installed, the electrical signals will be
transmitted properly. HI
Voltage
Ammeter
Test Description Source
LO
Connector Shell
Rpin1 Rpin2 Rpin3 RpinX
Riso Riso Riso Figure 2. Constant Voltage Method for Measuring High Resistance.
Riso Riso Riso Riso
Pin Continuity
As long-term performance of connectors becomes increasingly
important, the continuity performance from the input to the out-
Figure 1. Electrical equivalent of a connector showing pin continuity and put of the connector will also become more important. Typically,
isolation resistance. continuity is tested by sourcing a constant current through the
pin and measuring the corresponding voltage drop. Connector
Isolation (Insulation) Resistance pins are often made from metal alloys, so the measurement result
Essentially, the isolation measurement verifies that none of the is a very low resistance value. Pin continuity is shown as Rpin in
connector pins are shorted to each other. Given today's ever- Figure 1.
shrinking circuit geometry and the higher frequencies of elec- Using high currents to test continuity has two advantages.
tronics, isolation is an important consideration for reliability and First, using a sufficiently high test current ensures the resulting
minimizing crosstalk. A connector with no shorts today may voltage signal will be above the noise floor of the test system.
The ratio of the test current to the noise current will determine 2400 can output 210V, while the 2410 is capable of 1100V. Both
the signal-to-noise ratio and accuracy of the continuity test. supplies are limited to 22W. These output ranges mean that only
Second, higher test currents can also serve as a stress test for one measurement instrument is required for both isolation and
the connector. Often, the connector will be tested at a current continuity measurements, which greatly reduces programming,
level higher than the rated current level in order to verify cabling, and potential error sources.
performance margin.
Connectors typically contain many pins, so many measure-
If stress testing is unnecessary, a digital multimeter ment channels are required to test each pin. The most cost-
(DMM) with low voltage noise can be used to measure the pin effective way of adding measurement channels is to include
resistance directly. Figure 3 illustrates how a current source and switching in the test system. When switching is added, the user
voltmeter are used to measure resistance. Most instruments
can connect the SourceMeter instrument to specific points on the
designed to measure low resistances have a built-in current
connector for testing while simultaneously isolating other points.
source and voltmeter and can be configured to measure
Also, if a PC is added to the system to control the instrument and
resistance with one instrument bus command or button on the
switching, the entire connector test assembly can be automated,
front panel.
eliminating the need for constant operator oversight. Figure 4
illustrates a simple connector test configuration based on a
SourceMeter instrument.
HI
Current A SourceMeter-based connector test system is both cost
Source RContinuity Voltmeter
effective and easy to implement in terms of cabling, program-
LO ming, and complexity. Systems like this can typically resolve
signals as low as 10