making sense volume 1
TRANSCRIPT
8/11/2019 Making Sense Volume 1
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Making SenseVolume 1 – Insight for Engineers
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Table of Contents
Top Three Reed Switch No-No’s
3
Specifications versus Applications
4
Reed Switch Customization
5
Wisdom from the Design Journey
6
A New Solution to an Old Application
8
Making Sense Author Profiles
9
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Top Three Reed Switch No-No’sAuthor: Lawrence McClure
The reed switch: A simple electro‐mechanical device with a contact
area and two to three leads that, when the correct magnetic or
electrical force is applied, facilitates continuity through the switch.
Although simple in nature and application, we engineers sometimes
can get a little creative when it comes to the correct application of this device. Below are three
common “no‐no’s” that can help you get the best performance out of your reed switch.
No‐No #1: Treating a reed switch like a resistor
Whenever the reed switch leads are manipulated in any way, it can affect the magnetic properties of
the switch. For example, you cannot bend or cut the leads and expect to get the same magnetic
properties of the switch as when the leads are straight or at standard length. The switch is designed
with specific properties. It is recommended that any custom modifications, such as bending or cutting,
be done by the manufacturer, who can make sure that the resultant magnetic effect is understood
and that the hermeticity is maintained in the process.
No‐No #2: Dropping the reed switch or smacking it on a table
As obvious as it may sound, dropping the reed switch or even banging it up against a table‐‐as we’re
tempted to do when the switch is not operating as expected‐‐is not a very good idea. Due to the
properties within
the
hermetic
seal,
the
internal
workings
of
the
switch
are
highly
sensitive,
especially
in the smaller switches. If the switch does not work, replace it. Don’t break it.
No‐No #3: Overloading the reed switch
Again, it may seem self ‐evident, yet it occurs from time to time that a switch specified to a certain
load is pushed a little too far over the edge. The electrical specifications on the switch have been
tested and approved so for instance, loading a 250‐mA switch with 3 amps might not provide the
results that you are looking for.
I hope
these
fundamental
facts
about
reed
switch
application
will
prove
to
help
you
in
future
projects
and potentially save a lot of time on R&D and troubleshooting.
For more information about Reed Switch Basics, check out our Application Notes. Or, if you have other
questions about reed switch functionality, just ask. We’re here to help!
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Specifications versus ApplicationsAuthor: Zack McGillIt is challenging to create a general specification sheet for a product that exhibits application‐
dependent performance.
HSI
spec
sheets
are
meant
to
provide
users
with
useful
information
about
the expected performance of standard products. In most cases our reed switches are more capable
than the spec sheet ratings suggest, but safety factors are necessary to guarantee compliance across a
broad range of applications.
Let’s say that you are looking at a small Form‐C switch with rhodium contacts rated at 3W, 120V DC,
and 0.25A. Can you switch this reed at 120V DC and 0.25A and expect 10 million operations? No. The
effective load on this switch would be 30W…more than 10 times the maximum power rating! The
switch can be operated at max voltage, or max current, but not at the same time.
You are searching for a sensor that will operate at 0.5” and release at 1”. The spec sheet provides the
dimensions, electrical ratings, operation direction, and actuator part number, but you would like to
use a different actuator and you aren’t sure yet about the approach direction. The operational
information is specific to the actuator being used in the manner and orientation listed. An actuator
(magnet) can be purchased with a host of different parameters that affect the operational range of
the switch (size, shape, material, Gauss strength, field direction, etc.).
So what do you do if your application doesn’t exactly “fit” the spec sheet for one of our standard
products? Just give us a call or shoot us an e‐mail and we would be glad to provide specific application
assistance. That
switch
can
probably
handle
the
heavy
load
without
failure
if you
operate
it
at
a
reasonable rate and only need it to last for 100k cycles. If you need it to handle that load and still
reach 10 million cycles, we can provide a larger
switch, customize the Rhodium thickness to provide
a higher power rating, or provide you with a
tungsten contact switch. That sensor may work just
fine with your current actuator approaching from
the side instead of end‐on, but the operate and
release distances will differ from the spec sheet
listings. We
can
tune
a standard
product
or
custom
engineer a new sensor for your specific application.
HSI has the technical expertise to answer your
questions and multiple product lines to meet your application needs. Custom reed switches and
proximity sensors are what we do…better than anyone in the industry.
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Reed Switch CustomizationAuthor: Mark MandrellEach switch and sensor that we manufacture has its own particular characteristics, and how you
handle one
may
not
be
the
same
as
the
other.
Knowing
how
to
correctly
manipulate
a switch
is
very
critical to the proper operation of that device for its intended purpose. Many times we have
customers contact us with questions as to why they are experiencing problems when they are not
getting the results that they are expecting, or when damage to the switch occurs..
A reed switch may just look like a piece of glass with leads protruding from it, but really it is a very
intensely engineered special device that works in an amazing way,
and the methods used to customize it for your particular
application are very critical. The stresses induced at the time of
modification can
damage
or
severely
change
the
performance
from its original design function. A simple bend of a lead without
the correct gripping method can be all it takes for that device to
not work as it is intended, and this can lead to great frustration for
our customers.
With 45 years of leading the way in custom design and
applications for this industry, we here at HSI have engineered solutions to these production,
modification and testing processes. And let me tell you, we face new modification challenges every
day! To put it in the words of my great grandmother, “It’s like being a goose and waking up in a new
world every
day.”
This
has
been
my
experience
with
all
the
customer
applications
I’ve
seen
through
the years. It’s crazy (amazing?) to think about how many places and ways that our customers can
dream up of where and how to use our products; our customers put us to the test in a new way every
day!
When it comes to the tooling required to make necessary modifications to a product‐‐whether they
are requested by a customer for a specific application, or whether it is a requirement for the switch to
work precisely in one of our custom proximity sensors‐‐you can’t just go out and purchase it. We have
a fully equipped precision machine shop in‐house, along with machinist that have a combined
experience of
over
60
years,
and
we
design
and
manufacture
all
of
our
own
equipment
to
be
able
to
meet these special needs. From the machines that produce the switches, to the benders, the cutters,
the fixtures to perform the welding functions, the potting of the proximity sensors and the testing, we
do it all.
Please let us utilize our knowledge and ability to meet the unique needs that your project demands.
Our experience and expertise can save a lot of unnecessary frustration, damaged product, and the
most important project commodity of all that can never be regained, TIME!
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Wisdom from the Design JourneyAuthor: Eddie Shearer
In my
years
of
work
with
product
design
at
HSI
Sensing
I have
been
involved
with
many
projects
that
went very smoothly and also several that did not. Is there a key characteristic that largely determines
on which side of that fence a new project will land? I believe that there is.
In the broadest possible terms the phase at which we enter the project has the biggest impact on the
effectiveness of the solution we can provide. Ideally we want to be part of the design discussion from
the very beginning. We want to help with establishing the electrical circuit and also with the physical
constraints. Choices about component layout and material type greatly affect the outcome for
magnetically‐based switching and/or sensing solutions.
I do understand that many of the projects that reach my desk are retrofit applications. Someone (who
usually does not work at the company anymore) used a different solution originally, and now, for
whatever reason, need us to keep the same geometry but use a reed switch. Most of the time we can
still provide a solution in these difficult situations, but that is an article for another day.
Today I am talking about the design projects that are basically starting from a blank page. The
customer knows what they want the end result to do, but still they don’t call us right away. I can only
surmise that they oversimplify the reed switch. A reed switch is just a piece of glass with some
magnetically sensitive blades right? How hard can that be? They will go shopping online to find the
smallest switch
available
without
checking
the electrical ratings for that switch. They
end up allowing room for a small switch
but need the load capabilities of one five
or ten times the size.
I have seen occasions where customers
allowed space for a switch and a magnet
but didn’t understand the relationship
between the
two,
so
they
designed
the
magnet to deliver magnetism to the switch
in an inefficient way. By the time they are
able to test and realize it doesn’t work as
they planned, other things have been put
into place that prevent moving the magnet
and/or switch to make it work correctly.
There have been times when the designer did a great job picking the correct switch and providing a
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A New Solution to an Old ApplicationAuthor: David Posey
The world is full of mechanisms, machines and devices with moving
parts. Many of these "old" pieces of equipment or technology have
mechanical switches converting mechanical motions into electrical
signals. Often those mechanical switches get dirty, the contacts have
aged, or there are new requirements for environmental safety or
switch longevity or performance. There is always a fear that it will be
very difficult to replicate the exact performance of the old mechanical arrangement with a new
sensing method ‐‐ "difficult" can mean too expensive, too time intensive, or that the expertise doesn't
exist to make a fail‐safe transition.
Time and time again HSI Sensing is consulted to convert a specific mechanical motion into an electrical
signal. Most of the time we are assisting, guiding, or providing the full service for our customers to
convert the mechanical motion into an electrical signal. The pushback that sometimes occurs comes
from the perception that reed switch technology is not as capable as the old mechanical switches. This
often is true; however, we always ask “what signal are you actually switching?” The previously
employed mechanical switches are often rated 3, 5, or 10 amps switching capability. But in the new
application ‐‐ now typically signalling a computerized control system ‐‐ the rating is often below 0.1
amp. Hermetically sealed switches are very capable in these signal applications.
Mechanical switches are also activated by levers that sometimes move very small amounts. With the
correct type of magnet, polarity, switch type (engineered for close differential), and shielding, the
same motion can be achieved with reed switches fabricated into a proximity sensor. Now the sensor is
working in a "non‐contact" method. In other words, mechanical switches need a lever to move or a
button to be pushed, requiring physical contact that is also a method for wear. The reed switch‐based
proximity sensor has no need of physical contact.
Typical mechanical switches can be built with one or two sets of contacts. Reed switch‐based
proximity sensors can have one, two, three, or more sets of contacts in one proximity sensor housing.
If redundancy
is
needed
for
multiple
independent
signals,
this
type
of
assembly
should
be
considered.
Some may say reed switch technology is ancient ‐‐ it was invented in 1930s and 1940s. That is correct.
But the use of reed switches in various applications is far and wide. They are cost efficient in
manufacturing, simple to apply, require no power consumption to operate, and are hermetically
sealed for long life. Difficulty or simplicity is based on the knowledge of the application and how to
apply the technology. HSI Sensing has many years of experience in solving conversion of mechanical
motion to electrical signal. Contact us to see how we can help your conversion.
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Making Sense Author Profiles
David Posey, Chief Technology OfficerDavid didn’t invent the reed switch. But he spent 30 years perfecting it. He's
engineered solutions for pacemakers, jumbo jets, and for products like
submarines and the space station that push the boundaries of where we go
and what we do next. No one else in the world has seen all he’s seen, and
no one else loves putting that experience to work for you more than he
does.
Eddie Shearer, Product Development EngineerA mechanical engineer and 13‐year veteran at HSI Sensing, Eddie
understands that no two customer's challenges are alike, and he views the
task of custom engineering as a creative process.
"We start with a problem," he says. "At the end of the process we're holding
a device that solves that problem. It's the most rewarding thing I do."
Lawrence McClure, Product Design EngineerLawrence thrives on the intensity it takes to solve a customer's problem
without backing down, and he enjoys the process of using his mind and his
hands in tandem to engineer solutions to real‐world design challenges.
"The most rewarding thing to me is finishing a project," he says. "It's seeing
an idea come to life that started with just a sketch."
Zack McGill, Product Quality EngineerLike most engineers, Zack is a creative problem solver, and he loves putting
that skill to work for our customers. He believes when you push a product to
new limits and find new ways, everybody wins.
"You'd be surprised what a reed switch is capable of if given the chance," he
says. "We might even make it dance."
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Mark Mandrell, Senior Designer/Technical AdvisorMark was privileged to begin his 22‐year journey with HSI by learning
directly from its founder, Bill Posey, and experiencing first‐hand many
experiments and ground‐breaking products.
"It would be nice if you could open up a book and find that kind of
knowledge," he says. "I take great pride in being able to pass that
knowledge on in order to meet our customers’ needs."