Testing for the presence of a component or for the presence or length of a connector element is a common task in both PCB and wire harness testing. The important thing here is to find an effective and economical solution that is optimally matched to the space conditions on the one hand and the requirements for measurement accuracy on the other.
The simplest method of implementing a presence test with a spring-loaded contact probe is to use a simple switch probe. The switch integrated in the contact probe opens or closes a circuit after a defined travel. If a component is present, it presses the switch probe in when contact is made (e.g. by closing the test fixture), the switch is actuated and the presence is detected. If the component is not present, the switch probe plunger is not compressed, the switch is not actuated, and the fault is detected.
A variety of switch probes are available for this method. Depending on the available space, these can be very thin and compact probes, but for some applications, for example in wire harness and connector testing, very robust variants are also used in some cases. Depending on the application, switch probes are required as NC (Normally Closed) or NO (Normally Open) contacts, FEINMETALL offers both in a large variety.
Newly developed special switch probes with an off-on-off function allow much more precise position detection. While conventional switch probes have only one switch point after a specific stroke, these special switch probes have two switch points integrated at intervals of e.g. one millimeter. When the plunger is compressed, the switching circuit is closed after a defined travel and opened again after a further millimeter travel. This so-called off-on-off characteristic not only allows the presence to be checked, but also the correct position of the DUT to be determined by just one switch probe.
A typical application example is e.g. the length detection of connector pins, the detection of a correct hole depth in DUTs or the length detection of the plastic fastening during the clip test. Here the correct length or the fault case (too short or too long) can be detected. The special F48x switch probes have a very compact design and can be used in pitches down to 3.5 mm. This allows them to be used for position detection even in tight spaces.
In addition, a pneumatic micro switch probe with off-on-off switching function is also available (F899).
In addition to the simple presence test with a yes/no statement or a limitation to a specified tolerance range, an exact, quantitative determination of pin lengths or drill hole depths is increasingly required. In particular, the high quality assurance requirements in the automotive sector demand more and more exact and, above all, documentable measured values and protocols.
For these applications FEINMETALL has developed a perfect solution. The modular position sensor system can be used like a contact probe in a pitch down to 75mil, but contains a screwed-on sensor element with an integrated potentiometer. The voltage divider principle implemented with this allows exact and reproducible measurement of the plunger travel when an operating voltage is applied. The measurement data can usually be directly integrated into the existing tester environment and evaluated there.
An advantage is that the zero points or reference values can be easily set in the software before the measurement. To convert the measured voltages or resistances into millimeters, the system must be calibrated after installation. In addition to travel measurement, the test item can also be electrically contacted with the position sensor system. Thus, the position sensor has a total of four electrical connections, three for the voltage divider function and one galvanically isolated path as electrical contact to the probe tip.
For presence and position determination, there is an optimal solution for every need. FEINMETALL has taken a leading role for these applications and offers the largest portfolio of switch probes, whether pluggable or screwable, also with the possibility to change the probes without soldering.
You can find out more about automotive contacting in our catalog " Contact Probes for Wire Harness and Connector Testing".
Catalog pdf-download
All Specifications about switch probes can be found in our
