Just about anyone who ever takes a test measurement realizes that accurate data are dependent on the test tool’s design and capacity. Fewer people, however, understand the design quality and manufacture of the leads and connectors between the unit under test (UUT) and the test tool, are of equal importance.
It’s a plain fact that quality connectors are the one answer you need when a reliable and safe test signal is demanded. No matter how impressive the test tool, from a simple DMM to a high-end calibrator, the quality of the test leads is of equal importance to the tester. Whether in the lab, plant or in the field, using high-quality leads, plugs, and connectors can make a big difference.
The difficulty is one test lead or connector looks pretty much like another. And there isn’t too much difference in price between similar brands of good equipment. So, what’s the big deal about test leads and connectors, anyway?
At first glance, most people see test leads and connectors as merely a way to transmit data from the UUT to the test instrument. While that is partially correct, the variables are as big as the universe. Real-world applications involve a lot of questions such as what temperature, distance, current range, space available, contact requirements and so on. The list is endless considering how and when test measurements need to be taken and what data need to be acquired.
Test leads fall into two major categories: a.) Modular, where the leads are separate from the probes, and b.) Monolithic, typified by probes that are permanently attached to their probes. Modular leads offer the maximum in flexibility because standard probes can be removed and replaced by alligator clips, backprobe pins, grabbers and more. If you need to attach an alligator clip to a Monolithic probe, for instance, the clip needs to fit on the end of the probe which can end up being a long and tenuous junction that may affect your test readings.
The three parts of the test lead: the probe, the wire, and the DMM plug all are available in a host of combinations that run in the thousands of individual configurations. But each part deserves its own scrutiny. Some electrical probes are heavy duty and durable. Others, such as those for measurements on circuit boards require a trimmer probe configuration.
Probe tips also vary, depending on requirements. Electrical measurements call for heavy-duty stainless steel, whereas some have several removable tips to suit the board test application. There is even a probe with an extendable insulated tip allowing measurements between circuit boards without the fear of shorting them out in the test process.
- Safety . First and foremost are safety considerations for the user. With any electrical source, test leads must be designed to meet specifications of IEC1010. That means probes designed to satisfy the stringent voltage and category requirements of IEC1010 as they relate to CAT I, CAT II, CAT III or CAT IV.
Additional important requirements of the standard relate to transient tests, dielectric withstand voltage requirements or verifying by test that the product has sufficient insulation, current requirements, clearance spacing requirements, exposed metal probe tip requirements, impact requirements, markings and more. Good test probes are part of the personal protection equipment needs identified within NFPA 70E standards along with important personal protective wear, such as gloves and goggles, for effective overall protection of the user.
- Ruggedness and Durability . The simple act of using the test leads on a daily basis puts the probes, clips and internal wires of the test leads to trial. Under examination, quality test leads and connectors perform well in spite of being yanked and pulled, pushed and prodded. In short, good equipment is designed to take the abuse of daily use.
For example, leads should have well-designed strain reliefs at both ends of the wire. Hardened metal tips on the probes are necessary for repeated quality connections that transmit accurate data the first time, every time.
Specially manufactured multi-strand, tinned-beryllium copper wire instead of cheaper stock offers flexibility and long-term durability, excellent conductance and precision on which you can rely. Some manufacturers try to skimp on conductors but you pay the price at the expense of accuracy and flexibility. If you have ever had an intermittent “open” in a test lead, the implications are self-explanatory.
There are more considerations of ruggedness and durability, such as internal soldering qualities of probes and connectors as well as the temperature range of materials. For instance, at low temperatures some test leads make better coat hangers than test leads. Low temperature test leads definitely need to be made from silicone which is pliable at a range of temperatures.
- Design. The ergonomic design of probes and clips is of high importance, as well. Comfortable, easy-grip textures facilitate secure control in the hand and aggressive alligator teeth clips can make a big difference in maintaining positive contact. Connections should be easy and matched pieces should slide together without strain or pain.
Connectors, grabbers, plugs and clips come in more configurations than Noah had animals, but a few pointers will indicate if they are made to last -- or just made to sell.
he contacts on good connectors will be nickel or gold-plated machined-brass fittings, not just cast brass. Gold, however, provides the best combination of accuracy and resistance to oxidation that you can get, providing a long-lasting, secure, reliable connection.
- High performance applications . From sleek, light probes with spring-loaded tips for electronics test to rugged probes with stainless steel sharp points for industrial use, today’s probes are designed with the application in mind.
Some new applications fit the bill. They allow pin-point testing on surface mount boards (SMD) requiring very fine and sharp probe tips to accurately contact small board points. Also micro SMD clips are designed to fit the mini clamps, board mounts, BNC connectors, HDTV-ready applications with 75 Ohm capacity.
Micro SMD clips are now needed to grab the close-pitched legs of SMD chips. BNC breakouts (little patch cords with tiny wires) add to the ease of signal testing from board-mounted RF connectors. In addition, adapters are made to connect micro SMD clips to scope probes. Finally, IC clips enhance your ability to probe IC I/O when it’s installed on the board.
- DMM plugs . Many plugs are available to suit every application safely. They may be right-angle for DMMs, straight for bench applications on bench instruments and sheathed for safety that meet IEC1010 requirements. There are also unsheathed plugs available for older DMMs such as Amprobe and Simpson DMMs.
Whether you see it in a catalog or dream up a test lead or connector to meet your specific needs, there are many ways to find answers to your test problem. You can quickly find complete product specifications and discover new product announcements when you visit a manufacturer’s Website such as www.pomonaelectronics.com. It is as simple as selecting a category of accessory and finding a range of test solutions. Integral search engines can direct you to the product you are seeking.
Because technical questions about products or applications can arise almost anywhere, a few sources offer toll-free technical support. A qualified technical resource can be readily contacted via e-mail or phone. There you can also request selector guides, request a catalog, or get specific product information you seek.