App. Note 9 - Robotics
(Reduction of Electronic Smog Effects in Robotics by using Stabilants)
"Electronic smog" is a term coined to cover electromagnetic interference
from any source, whose potentials could affect the operation of robotic
equipment. Obviously it is a term that could apply to almost any field
where complex electronic equipment is being used, from biomedical electronics
to avionics. Advancements in IC design have made it possible to reduce
the power level of signal lines in electronic equipment, with worthwhile
savings in power as well as in the size of electronics packages, but this,
in turn, has made equipment more susceptible to outside electromagnetic
interference.
What are the normal procedures for combating electronic smog?
There are two main steps involved:
- Reduction of electromagnetic radiation from equipment
- Reduction of the susceptibility of equipment to electromagnetic interference
These translate into such things as better shielding of equipment both
from the containment point of view of the former, and from the exclusion
point of view of the latter. Often it is difficult for a factory to control
external sources of electromagnetic radiation (such as Radio & TV transmitters),
and they must concentrate on reducing the damaging potential of electronic
smog.
Robotics is especially susceptible to electronic smog, and in Japan,
several deaths have been attributed to the malfunction of robotic equipment
caused by outside electromagnetic interference.
While electronic smog may be combated through the use of better shielding
design, this is of little use to equipment that is already installed.
In existing equipment the procedure is usually one of making sure that
existing shielding is properly installed, all signal and power leads are
protected by shielding, and that connector integrity is good. What is not
always appreciated is that thin film rectification effects, can convert
a poor connection into a radio receiver, and thus produce anomalous signals
in the circuit using that connection. This is especially insidious in factories
where the atmospheric environment may contain chemicals which will cause
connector corrosion, or general breakdown.
Many of the corrosion products encountered in connectors are semi-conductors.
Although most robotic equipment is designed with environmentally secure
connectors, once it has been in use for several years the integrity should
be suspect.
What else can be done?
If all the electromechanical connections in the equipment itself, and
all its connections to outside equipment are treated with a material which
minimizes or eliminates thin film or point-contact rectification effects,
the susceptibility of the equipment to electronic smog will be reduced.
It is also important that the shielding enclosures form a continuous shield.
In this respect some equipment's shielding may be rendered ineffective
by the painting of the shielding cases in the areas where the covers are
screwed together. Sometimes spring "finger-stock" is used to ensure that
a cover is sealed electronically all around its edges. Obviously, any paint
on the finger stock or its associated contact surface will render the protection
ineffective.
The same can be true of corrosion or tarnish on the surface of these
shielding devices. Thus it may be necessary to treat the finger stock with
a contact enhancer.
Stabilant 22 has proved to be effective at reducing the RF susceptibility
of many different types of connectors.
What is Stabilant 22?
Stabilant 22 is an initially non-conductive block polymer that
under the effect of an electrical field and/or when used in a very
narrow gap between metal contacts, becomes conductive. The electrical
field gradient at which this occurs is set so that the material will remain
non-conductive between adjacent contacts in a multiple pin environment.
Thus, when applied to electromechanical contacts, Stabilant 22 provides
the connection reliability of a soldered joint without bonding the contact
surfaces together.
While Stabilant 22 exhibits surfactant action it is not sold as a contact
cleaner. Equally, it exhibits quite good lubricating properties but is
not sold as a contact lubricant. Its métier is in its active properties
when used in a connection and its other properties are a bonus.
Where it can be used?
Stabilant 22 can be used wherever electrical contacts are used,
whether this is in connectors, or in switches. For example, one common
use is to improve the connection reliability of socketed IC's in computers.
In combating the effects of electronic smog, every non-power-interrupt
connection in a system should be treated.
Why should we use Stabilant over less expensive alternatives?
Granted that the material itself is expensive. However it is unique
in having a very long useful life once in place. Unlike other so-called
contact treatments Stabilant 22 will not cross-link (becoming varnish-like)
under the action of sulfur-based curing agents in elastomers, cutting oil
residues, or the sulfur-bearing free-machining metal alloys used in some
contacts. Thus, in combating electronic smog through the use of Stabilant
22, other connector-related problems will be prevented increasing the
mean-time-between failure of the equipment. In most types of service work,
the cost of the time involved in removing and replacing a board will be
much greater than the cost of the Stabilant used to treat the board. Here
what is important is that not only will proper board treatment cure existing
contact problems, it will prevent others from occurring thus eliminating
the necessity of repeating the treatment at a later date! In other words,
why do a job more than once?
In addition, Stabilants are one of the few viable alternatives to the
repeated use cleaning solvents in electronic maintenance and manufacture,
and thus are not subject to the increasingly stringent and restrictive
legislation applicable to solvents.
In what forms is Stabilant available?
Stabilant 22 is packaged in 15mL, 5OmL, lOOmL, 25OmL, 5OOmL
and 1 Liter containers. Stabilant 22 is available in several forms.
When it is a concentrate it is called Stabilant 22, when it is used
as an isopropyl alcohol-diluted form, it is called Stabilant 22A.
Conversely, when diluted with ethanol, it is called Stabilant 22E.
Because of the 4:1 dilution, a given size container of Stabilant
22A (for example) will cost about one-fifth the amount of a container
of Stabilant 22, for it has only one-fifth the amount of the concentrate
in it. Another packaging is available for industrial-bulk users. Stabilant
22S packages the concentrate such that it occupies one-fifth the volume
of an otherwise empty container. This allows the end-user to add his own
diluant and saves the added cost of shipping isopropyl alcohol, as well
as allowing the end-user to use an alternate diluant such as one of many
other solvents.
What is the difference in use of the Stabilants?
The concentrate, Stabilant 22 is most useful where the connections
are out in the open such as the card-type connections. Where the connections
are not too easy to get at or where the user wishes to apply the material
to something such as a socketed IC (without removing the IC from its socket)
it is easier to use the alcohol diluted form, (e.g. Stabilant 22A).
The alcohol diluant serves only to carry the concentrate into the connector.
Is it available in a spray can?
Not at present. During the initial stages of our market research we
did provide cans of the material, but the users found that in most cases
it did not ease the application of the material, wasted many times the
amount that actually got on the contact areas, and generally left a film
of excess material that had to be cleaned up for appearances sake.
There was another consideration - this was that the fact that chlorofluorocarbon
propellants might have been used. Although they are no longer used in spray
cans, a HCFC is now substituted. However, although they are less harmful
to the ozone layer, they are still a problem. Sometimes spray cans may
use a highly inflammable mixture of Butane and Propane being substituted.
Remember, very little Stabilant 22 is necessary to treat a contact, so
why waste it?
Is Stabilant just another contact cleaner?
No, it is important to remember that Stabilant 22 is an electrically
active material which enhances conductivity within a contact without
causing leakage between adjacent contacts. Thus large quantities of the
material do not have to be "hosed" off as is the case with cleaners.
Just how much should be used?
Normally, a final film thickness of from 0.5 to 1 mils of the concentrate
is all that is necessary. In other words you want just enough to fill up
the interstices between the contact's faces. Where you're using Stabilant
22A, you'll have to use enough so that once the alcohol evaporates
the desired 0.25/0.05 to 1 mil film of Stabilant 22 remains.
What is the 15ml service kit?
This was made up at the request of several manufacturers who wanted
a standard kit that they could issue to their service personnel. It consists
of a 15mL container of Stabilant 22A and some Q-tips- as applicators,
all in a small capped tube. The applicators are reusable.
Why would anyone want to buy a half-liter of the concentrate?
Some manufacturers make large volume purchases, diluting the material
as required for specific applicators used on their production lines.
Many end users have found that the material cuts their service costs
so much that it is more economical to purchase Stabilant 22 in the
larger size container, with its attendant savings, rather that run any
risk of being without the material. The number of uses tend to increase
as customers discover the diversity of the problems that can be solved
by the material. One user routinely applies it to the flashlight switches
and batteries it issues to its security guards and has reported that the
number of requests for both batteries and replacement flashlights has dropped
appreciably.
How can I be sure that the material works?
We could cite the fact that Stabilant 22 is used by many hospitals
on their bio-medical electronics to improve reliability of the equipment
where lives are at in the balance, we could cite the use of Stabilant 22
by many broadcasting networks to achieve the last measure of reliability
in critical network switching applications, we could cite its use in navigational
aids, or we could cite the years of use in the audio field where even consumers
found the material easy to use and its results impressive; but we still
feel that the best way to find out just how well it works is to try it
out!
That's why we have samples available. Almost every service shop or manufacturer
has equipment available where the switches or connectors have become erratic
over the years. Use Stabilant 22A on them for a quick turnaround
test, or use the material in field service and satisfy yourself.
Is the material hazardous?
Stabilant 22 has caused no skin reactions in tests. Because
of its moderate detergent action it could remove skin oils and lead to
chafing, therefore skin spills should be washed off and a lanolin-type
lotion applied. In the undiluted form, Stabilant 22 is non-flammable,
however if its temperature is raised above 200' C the decomposition products
will burn. If small amounts are accidentally orally ingested it will cause
bowel looseness. while ingestion of amounts in excess of 200 mL of the
concentrate could lead to systemic collapse! Stabilant 22 has an
LD50 of about 5 grams per kilogram body weight.
Can it be used by untrained personnel?
The consumer version of Stabilant 22 which was sold as TWEEK(TM)
had been used for fourteen years without problems.
What is the best way to apply it to a contact?
The 15mL and 50 mL containers have a "dropper" type cap that allows
Stabilant
22A (or 22E) to be applied directly to such components as socketed
IC's, switches, connectors, etc.
Some end users prefer to buy larger quantities and use industrial syrettes
to apply the material onto connections. Camel's hair or sable brushes can
be used to brush it on card-edge connectors. Cards can also have their
edge connectors dipped into the dilute material.
In treating "finger-stock" electronic seals, the concentrate, Stabilant
22 may be wiped on just as if the technician were using a protective
oil.
Does the action of Stabilant 22/22A/22E deteriorate with age?
Stabilants have been in some field trial applications for over
fifteen years now without showing any sign of reduced effectiveness. The
material has a high molecular weight and a very low vapor pressure, thus
it is not prone to evaporation.
Once again let us emphasize the point that unlike some other contact
treatments containing oils, Stabilant 22 will not cross-link when
exposed to certain materials such as high-sulfur brass, or when used on
connectors having elastomer or the most plastic components with accelerant
and curing agents, or when used on contacts where cross-link promoting
agents are present in the environment. The phenomena of "varnishing" does
not occur with Stabilant 22.
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