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
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
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
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
- 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
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.