In both PCB and wire harness tests, a common application is to verify the presence of a component or the presence or length of a connector element. Here, it is important to find an effective and economical solution that is perfectly adapted to the available space on the one hand and to the requirements for measuring accuracy on the other.
1. Presence test with standard switch probes
The simplest method to realize a presence test with a spring contact probe is the use of a standard switch probe. The switch integrated in the probe opens or closes an electric circuit after a defined travel. If a component is present, it presses the plunger in during contacting (e.g. by closing the test fixture), the switch is activated and the presence is detected. If the component is not present, the plunger of the probe is not pressed in, the switch is not activated and the fault can be detected.
A large number of switch probes are available for this approach. 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, often very robust versions are used. Depending on the application switch probes are required as NC (Normally Closed) or NO (Normally Open) contacts, FEINMETALL offers both in a large variety.
> to the product finder (Tip: Select the characteristic "with switch")
2. Switch probes with two switch points (off-on-off)
A much more precise position determination can be realized by newly developed special switch probes with an off-on-off function. Whereas conventional switch probes only have one switching point after a specific travel, these special switch probes integrate two switching points at a distance of, for example, 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 presence tests, it also provides the ability to verify the correct position of the test object with just one switch probe.
Typical application examples are the length detection of connector pins, the detection of a correct hole depth 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 identified. The special switch probes F48x have a very compact design and can be used in centers down to 3.5 mm. This enables position tests even with limited space.
In addition, a pneumatic micro switch probe with Off-On-Off function is also available. > F899
3. Exact length measurement with position sensor system
More and more frequently, in addition to the simple presence test with a yes/no statement or limitation to a specified tolerance range, an exact, quantitative determination of pin lengths or drill hole depths is also required. In particular, the high quality assurance requirements in the automotive sector increasingly demand exact and documentable measured values and protocols.
FEINMETALL has developed a perfect solution for these applications. The modular designed position sensor system can be used like a contact probe in centers down to 75mil, but includes a screwed-on sensor element with an integrated potentiometer. The implemented voltage divider principle allows the exact and reproducible measurement of the plunger travel when an operating voltage is applied. The measured data can usually be directly integrated and evaluated in the existing tester environment.
An advantage here is that the alignment of the zero points or reference values is simply done with the software. To convert the measured voltages or resistances into millimeters, the system must be calibrated after installation. In addition to the positioning measurement, the test object can also be electrically contacted with the position sensor system. Accordingly, the position sensor has a total of four electrical connections, three for the voltage divider function and a galvanically isolated path as electrical contact to the probe tip.
For all different presence and position test requirements there is an optimal solution. FEINMETALL has taken a leading role for these applications and offers the largest portfolio of switch probes, whether plug-in or screwable, also with the ability to change the probes without soldering.