The specifications and parameters seen in connector datasheets provide the important data needed to select the connector.
Basics of connector specifications
As might be expected there is an amount of terminology and specifications associated with connectors. The different connector types as well as the basic formats and the different types of specification.
- Plugs and sockets One of the basic concepts of connectors is that there are two different formats for connectors. One is the male, or plug, and the other is the mating half that is the socket, receptacle or female section. The male section has pins, and these are often exposed and therefore plugs are never used to supply power. This would mean that when not connected the accessible pins would be live and there would be a significant risk of them becoming shorted. Instead the female connector can supply power. The contacts in the female connector are more protected and therefore it is safer to have power on them while there is no mating connection.
- Number of pins When choosing any connector type it is necessary to determine how many pins will be required. This may not only determine the actual connector part, but also the series of connector to be used. When choosing a particular connector it is standard practice to ensure there are a few spare pins for any future unforeseen requirements.
- Number of insertions All connectors have a finite life. It is obvious that they will wear each time they are connected and disconnected. Often the life of a connector is specified in terms of the number of mating cycles, i.e. a connection and disconnection. Some connectors that are intended to enable a piece of equipment to be assembled and then are intended only to be disconnected for service and repair may only have a small number of mating cycles. Others for more general use will have a much larger number. This specification may obviously affect the type of connector chosen for a particular applications.
- Mechanical considerations There are a number of mechanical considerations when choosing connectors. Physical size and shape is an important factor, but there may also be environmental requirements. Will it operate over a given temperature range, or withstand moisture. These and other mechanical aspects need to be considered when choosing the type of connector.
- RF and screened connectors Sometimes there are special electrical requirements. One particular case is where the connector requires screening to be contiguous through the connector, or for more exacting requirements where the connector forms part of an RF feeder. In these cases the connector may need to be coaxial in nature, where the two conductors are manufactured so that one surrounds the other. For RF connectors the requirements may be more exacting because the characteristic impedance of the feeder needs to be maintained through the connector.
- Current capability An important element for any type of connector is its current capability. Some connectors are only designed to carry small currents, whereas others are able to carry much larger levels. Normally it is only necessary to consider higher current levels, as most connectors can take a few milliamps without a problem. However when looking at low current elves it is necessary to ensure that a good quality connector is used. Some low cost varieties may form oxide layers that need a certain level of current to flow to enable a good low resistance contact to be made. If currents of a few milliamps or microamps are to be carried, they may not perform well. Often gold plated contacts may be required for the more exacting applications.
It is often found that the current carrying capacity of a pin is not quite adequate. One solution that is often used is to use two contacts instead of one. The drawback is that the current may not be shared equally between the two contacts and one may exceed its rating. When adopting this approach it is best to leave a large overall margin to ensure that all pins will operate well within their capability.
- Voltage capability there is a maximum operating voltage for connectors. Above a certain voltage it is not safe to operate a connector. While virtually all connectors will be suitable for low voltages, when they rise to what may be termed hazardous voltages, care needs to be taken as insulation may fail, or there may be flash over. Accordingly it is always worth ensuring that the maximum voltage is not exceeded. Specifications may be provided for AC and DC.
- Insertion force When connectors mate, there is a certain level of friction between the contacts. This enables good contact to be made, and the contacts to be cleaned. For many small connectors, this is not a problem. But for many larger connector types with a large number of pins, the force per contact is multiplied by the number of pins used, and this can result in a large amount of force being required to connect and disconnect the connectors. This can be a problem in some instances, and may need to be considered. For some specialist applications where very large numbers of pins are required, what are termed "Zero Insertion Force" (ZIF) connectors may be used. When mating, the female connector does not allow the male pins to contact the female mating pins, thereby considerably reducing the force. A lever on the side of the female connector brings them into contact once the two halves have mated. This reduces the insertion force to a very small value.
The choice of connector can play an important part in the deign of any equipment. Even when using connectors for home applications it is often useful to have a good understanding of their capabilities and an idea of the key specifications for different types of connector.