Table of Contents:
- 1. Basic Definitions and Areas of Application
- 2. Design Types and Principles of Operation
- 3. Differences of Inch & Metric Sized Probes
- 4. Materials & Production Processes
- 5. Contaminations, Protection by Nano Coating
- 6. Physical Constraints
- 7. Pointing Accuracy & Wobble
- 8. Service Lifetime
- 9. Electrical Resistance
- 10. Receptacles & Terminations
10. Receptacles and their Terminations
To facilitate the handling of spring probes within a test equipment, normally receptacles are used which take up the individual probes. This arrangement is particularly useful, as the spring contact probe is a wearing part and should be easily replaceable without detaching the wiring.
Nevertheless, the connection between receptacle and spring contact must be of high quality from an electrical point of view: the current must flow from the plunger via the pin housing to the receptacle and finally into the termination wire.
10.1 How is the Spring Contact Probe being fixed in the receptacle?
The following methods are used to hold the spring contact probe tight in its position in the receptacle:
a) The receptacle has several dimples or beads which impose a slight pressure on the housing of the spring contact and thus fix it in its position. Use small pliers to pull out worn probes and replace them with new ones. This procedure is standard in the test area.
b) Dimple plus snap-groove. As already described in a) the receptacle has several beads or dimples. Additionally, it features a circular constriction at the bottom end, exactly where the inserted mating spring contact has its corresponding groove. The resulting retention force is considerably larger than described in a) – as a consequence, also the installation force is much higher. Scope: Cable harness test, connector test.
c) Slightly bent spring contact probe. Principle of operation: Here the receptacle is designed as an open tube without any bead. The spring contact probe is slightly banana-bent in the bottom area . Once inserted into the receptacle it is “clamped” in the cylindrical guide tube. Retention force is comparable to a). Idea behind it: The spring contact probe is a wearing part and will be replaced from time to time. The receptacle, however, should remain in service as long as possible. Beads in a receptacle may fatigue after several pin replacements. Therefore, the required retention force feature is moved into the consumable.
d) Screwed connection. When extremely high retention force between receptacle and spring contact probe is required, screwed designs come into play. The spring contact has a male thread, either at the bottom end or near the collar. The receptacle features a female thread. To prevent the screwed connection from self-loosening (caused by vibrations) the receptacle may provide additional beads.
10.2 Receptacle Terminations
The receptacle is connected with the test equipment via wire or printed board. The following termination styles are available in our standard product range. The ID code is included in the article number:
|C||Crimp Terminal||Receptacle has an open end for crimping a stranded wire.|
|L||Solder Cup||Formed or milled open solder cup. Solder stranded wire from aside.|
|LO||Open Solder Terminal||The open end is slant cut, similar to a soldering lug.|
|W||Wire-Wrap||With Wire-Wrapping-Post 0.64 x 0.64 mm, suitable for wire AWG 26 - 30.|
|RP||Round Post||Round post, 0.63 mm ø, suitable for various connector sockets or THT soldering.|
|CD||Crimped with wire||Receptacle has pre-attached wire .|
|O||Open End||Suitable for plug-connections or for soldering a wire.|
|NT||No Terminal||Receptacle without special terminal type, normally pressed into a p.c.b. via hole.|
|F||Fast-On-Plug||Tab (Fast-On) directly at the receptacle.|
|B||Only for pneumatic probes||Electrical connection via lateral attachable clip, additionally to the axial termination for air hose.|
|G||Spring loaded end||For use in wireless fixtures, connection to a translator p.c.b. pad or trace via spring loaded plunger.|
Additional customer specific terminations on request.
10.3 Receptacle Styles - Pressring or Collar
As already described in chapter 3 of this handbook, there are different basic principles for the installation of receptacles:
- With press ring(s) (pressed-in installation)
- With limit collar (collar seated installation)
If you use a press ring type receptacle, make sure that the mounting hole has a slight chamfer. This is particularly important for very hard base plate materials like FR4 (G10). The press ring must be capable of sliding into the mouth of the hole, then it is slightly constricted (caused by press-in pressure that leads to a minimal longitudinal extension of the receptacle) and in its final position the ring provides permanent clamping. The press rings of the receptacles can only be manufactured in deep-drawing technology where this outward bulge is upset. This technology provides the required flexibility to create a permanent, tight connection. Nevertheless, under certain adverse conditions it may happen that a pressed-in receptacle will slightly slide-down in its hole. As a consequence, the installation height of the spring contact probe is incorrect: the probe head is seated too low. Often this isn’t immediately noticed. The main cause is incorrect handling during probe replacement.
Users must not forget that these products are sensitive, high-precision parts which should be handled with great care. Some series feature styles with several press rings arranged one above the other. One is intended to provide permanent clamping. The other, slightly smaller in size, shall optimally align the receptacle in the drilled hole. This design for receptacles improves the pointing accuracy when compared with models which feature only one press ring. Receptacles with cylindrical shafts are anyway seated perfectly aligned in the mounting hole. To improve retention force, some variants feature an outside knurling directly below the limit collar.
10.4 Press-in installation of Receptacles
The assembly of receptacles should be done with great care. The insertion force should be – whenever possible – perfectly vertically aligned without any lateral movement. We recommend the use of an equipment with vertical spindle like e.g. a bench drill or an upright drilling machine with an inserted press-in tool. Receptacles with press ring generally feature a straight-cut mouth. Here a steel mandrel can be used as press-in tool. Its face should be precisely grinded at right angles to the longitudinal axis with its diameter slightly larger than the receptacle itself.
The receptacles are pre-plugged into the drill holes and slide down to a certain extent. Then they must be pressed-in to their final position. Put the carrier plate on the machine table with precision distance blocks underneath. Use the prepared mandrel to press-in all receptacles. Do the insertion in several steps and release the mandrel between the steps. You can press-in completely until the mouth of the receptacle is flush with the surface of the carrier plate. Or you can leave a certain receptacle extension height. To ensure a consistent press-in depth you can adjust the machine stopper. However you will obtain higher precision when the press-in tool features its own limit stop, e.g. a lock bush. But finally, the best approach is determined by the skills of the person in charge of the assembly. There are press-in tools available on the market which feature an additional centering pin which should be regarded with great care. Successful use of this centering pin stringently presumes that the receptacle to be pressed-in is perfectly aligned with the axis of the press drive shaft. Slightest deviations could damage the receptacle. A flat tool without a centre pin allows for greater tolerances here.
Hint: When receptacles with solder cup are to be installed, it would be wise to align the orientation of the cups before insertion. Properly aligned cups are easier to solder when it comes to multi-pole receptacle arrangements. There’s another point that should be considered for receptacles with limit collars like e.g. S 30.00-xx: This receptacle has a trumpet-shaped mouth, i.e. it is chamfered. If you apply too much force on this “trumpet end” using a flat tool, it can come to a deformation of the mouth. For that purpose a special tool with undercut is available that prevents such deformation and provides excellent results. Therefore, for receptacles of series 30 use only our original insertion tool SEW-30!