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The
following solenoid design considerations will need to be
evaluated when you discuss your application with us.
The
initial information you will need for selecting a solenoid
is a reasonable approximation of your required stroke (or
rotation), force (or torque), and duty cycle. Cliftronics
engineers will help you fine tune these requirements as
the design develops and prototypes are tested.
1. STANDARD OPERATING CONDITIONS
For
uniformity of data, the standard operating condition for
solenoids in our catalog is defined as a 20°C ambient
temperature with the solenoid mounted on the standard heat
sink which is listed for each solenoid size in our catalog.
2.
STROKE OR ROTATION
The
stroke (linear solenoids) or rotation (rotary solenoids)
is the total armature travel or rotary shaft motion expected
when electrical power is applied to the solenoid. For greatest
efficiency and smallest size, you should design for the
shortest stroke or rotation possible.
The unit value of linear stroke is inches and the unit value
of rotary stroke is degrees of rotation.
3.
FORCE OR TORQUE
The
force (linear solenoids) or torque (rotary solenoids) is
the load that the solenoid is capable of pulling, pushing,
holding or rotating, at the start of a specified motion,
when energized under a specific set of operating conditions
(input voltage, ambient temperature and duty cycle).
The
unit value of force is pounds (lbs.) and the unit value
of torque is inch-pounds (in.lbs.). Note: One pound of force
applied on a one-inch radius arm is one in.lb. of torque.
4.
FORCE OR TORQUE VS. TEMPERATURE
For
a specific solenoid stroke or rotation, the solenoid force
or torque will decrease as the solenoid coil temperature
increases. Conversely, the solenoid force or torque will
increase as the coil temperature is lowered. This is a result
of proportional changes in the coil wire resistance with
changes in wire temperature (see 16: COIL TEMPERATURE AND
PERFORMANCE / RESISTANCE FACTOR). The higher the wire temperature,
the higher the coil resistance will be. Since essentially
all power input to the coil is converted to heat, a more
efficient heat sink, greater airflow and a cooler environment
will cause the solenoid to produce more force or torque.
The
force and torque values shown in our catalog are the results
of actual tests conducted with the solenoid coil temperature
at room ambient. In actual service, the solenoid forces
and torques will vary from the catalog values depending
on actual coil temperatures. In your preliminary solenoid
selection, we recommend allowing a 50% safety margin in
your force or torque calculations to compensate for this
coil heating.
5.
COIL TEMPERATURE RATINGS
The
standard coils listed in our catalog are designed to achieve
a stabilized coil temperature of 125°C when operated
at the rated power and duty cycle, under Standard Operating
Conditions. We design our coils in this manner to allow
moderate temperature increases in your application environment
without exceeding the 175°C rating of the standard coil
insulation components. In higher temperature applications,
custom coil windings can be designed which utilize higher
temperature wire and insulation systems.
To insure
that the coil selected for your application does not overheat,
our engineers will calculate the expected maximum stabilized
coil temperature for your application if you provide us
with the power input, duty cycle, ambient temperature and
heat sink information. These calculations will also help
you confirm that you are not under powering the solenoid
in your application.
6.
MAXIMUM STABILIZED COIL TEMPERATURE
This
is the temperature at which a solenoid coil will stabilize
when energized with the maximum power input and subjected
to the maximum ambient temperature of the application. Cliftronics
standard coils are designed to withstand a 175°C maximum
stabilized coil temperature (abbreviated MSCT).
7.
HEAT SINK
The
standard heat sink is designed to be approximately twenty
times the surface area of the solenoid. It stabilizes the
solenoid temperature by dissipating the coil-generated heat
at the same rate as power is being applied to the solenoid
coil. While your application heat sink (mounting bracket
or flange) may be a different shape than the standard recommended
heat sink, the overall surface area should be approximately
the same. Use of smaller than recommended heat sinks will
cause the stabilized coil temperature to increase unless
compensation is made by reducing the power input, reducing
the "ON" time for each cycle, increasing the "OFF"
time between cycles, increasing the air flow around the
solenoid, or by reducing the ambient temperature.
8.
COIL HEAT DISSIPATION
Cliftronics
standard coil/housing construction allows effective transfer
of heat from the coil winding through the iron housing to
the heat sink. To reduce stabilized coil temperatures, or
to allow increased power input to the coil, thermal transfer
between the coil and housing can be further improved by
utilizing epoxy potted or impregnated coils. Coil potting
also serves to improve environmental properties such as
shock and vibration resistance.
9.
DUTY CYCLE
The
timing of a solenoid cycle or duty cycle is normally defined
by the application. It is the percentage of coil "ON"
time to the total actuation cycle time as shown in the following
equation:
10. CONTINUOUS DUTY
Cliftronics
standard solenoids are designed to achieve a stabilized
coil temperature of 125°C when operated continuously
at the listed continuous duty rated power input under standard
operating conditions. Our standard unit coils are designed
in this manner to allow moderate temperature increases in
your application environment without exceeding the 175°C
rating of the standard coil insulation components.
11.
INTERMITTENT DUTY
Higher
forces than available at continuous duty operation can be
achieved by applying higher power levels to the solenoid.
However, increasing the power input will result in higher
coil temperatures, which will exceed the coil temperature
rating unless the power is applied intermittently. The maximum
"ON" time must be controlled and must be short
compared to the "OFF" time between power applications,
allowing the solenoid coil sufficient time to cool between
actuation's.
Cliftronics
standard solenoids are designed to achieve a stabilized
coil temperature of 125°C when cycled at the intermittent
rated power input, observing both the maximum "ON"
time listed in each data table and the standard operating
conditions (20°C ambient temperature and standard heat
sink). The percent duty cycle must be maintained ("ON"
time vs total cycle time) to insure that the maximum design
coil temperature is not exceeded.
COIL
WINDING DESIGN
12.
OHM'S LAW
Voltage,
current, and coil resistance relationships are defined by
Ohm's Law as follows:
Voltage
(E) = Current (I) x Resistance (R)
Other
helpful relationships are shown in this chart:
VOLTAGE
= E (Electromotive Force); Volts
CURRENT
= I; Amperes
POWER
= W; Watts
RESISTANCE
= R; Ohms
13. VOLTAGE / RESISTANCE
Coils
may be wound and resistance adjusted for any DC voltage.
Those most commonly specified voltages are 6, 12, 24, 48,
and 100 VDC. Standard coil windings, available for all standard
Cliftronics solenoid configurations are listed in our catalog.
14.
COIL CURRENT
For
any catalog item, once you determine the power required
to generate the necessary force, the coil current may be
calculated as follows:
15.
COIL RESISTANCE
After
you determine the required coil current for your application,
the approximate coil resistance value may be calculated
as follows:
Cliftronics
standard coil resistance values for each solenoid size are
listed in our catalog. The coil winding with the coil resistance
closest to your calculated value should be the best initial
choice for your prototype testing. Our engineers will help
you compensate for temperature, duty cycle and other application
variables to insure selection of the most appropriate coil
winding for your solenoid.
16.
COIL TEMPERATURE AND PERFORMANCE / RESISTANCE FACTOR
It
is known that the resistance of copper wire will change
by .393 percent for each degree the wire temperature varies
from 20°C. This proportional change in resistance is
called the resistance factor and can be utilized to predict
how a solenoid will perform at high or low temperatures.
(resistance factors are listed on page 47 in our catalog)
If we call t2 any other temperature, the proportion is defined
as:
For
example, a solenoid with a 100 ohm coil at 20°C is designed
to stabilize at 125°C with a 24 VDC continuous duty
input. The resistance factor for the coil at 125°C may
be calculated as follows:
Rf
= 1 + .00393 (125°C - 20°C) = 1.4126
The Resistance of the coil can be calculated:
R20°C
x Rf = Rt2
100
ohms (@ 20°C) x 1.4126 = 141.26 ohms
Using Ohm's Law, E = IR, the current for this coil at 125°C
will decrease in the same proportion that the resistance
increases. The current for this coil at 20°C is:
Therefore, the current for this coil at 125°C will be:
Force
or torque may be predicted for this solenoid at 125°C
by applying a current of .17 amps to the unit at 20°C.
The actual coil stabilized temperature may be determined
by measuring the proportional change in resistance with
temperature. After applying the 24 VDC application voltage
to the example solenoid for a sufficient period of time
to allow the coil temperature to stabilize (approximately
1 hour), the coil current or resistance could be measured.
In this case, the actual current would be .17 amps and the
resistance would be about 141 ohms.
Setting up the proportion:
Rearranging
the Resistance Factor formula to solve for temperature t2:
Once
a stabilized coil temperature has been determined for a
specific application, we can predict the performance of
that unit for any set of application variables such as voltage,
current and temperature.
17.
SPECIAL COILS
Cliftronics
standard coils are wound to stabilize at 125°C when
operated at the rated power input and duty cycle under standard
operating conditions. Since many applications require different
power input and/or operate under different ambient temperature
conditions, our engineers will design special coil windings
to meet your special needs. Please discuss your special
requirements with us.
18.
TWO COIL WORK/HOLD
Two
coil units offer ideal solutions for applications where
solenoids must be energized for long periods and where physical
size and weight of the continuous duty solenoids are a problem.
The two coil designs combine the smaller size advantage
of the intermittent solenoid with the lower power consumption
of the continuous duty design. The work or pull-in coil
operates at the high power levels of the intermittent duty
solenoid and moves the load through the complete stroke.
At the end of the stroke, the second or hold coil is added
to the circuit. The two coils together, in series, hold
the load continuously at a power level which, in most cases,
is substantially below that of the conventional single coil
continuous duty solenoid. The "adding" of the
second coil can be accomplished by an external mechanical
switch or with a timed electronic driver circuit.
19.
DRIVER CIRCUITS
Electronic
driver circuits are available for various voltages and all
solenoid sizes. Designs are available for switching pulse
and hold, two coil solenoids and for Pulse Width Modulation
of power to single coil solenoids. Circuits will be custom
designed to meet your application and timing requirements.
Please call our engineers to discuss your Driver Circuit
application.
20.
RETURN SPRING
In
many linear and rotary solenoid designs, it is possible
to incorporate armature or shaft return springs, often eliminating
the need for external springs in your device. Please discuss
your spring requirements with our engineers so we can help
you evaluate your return motion load requirements and to
allow us to recommend a spring design to best suit your
application.
21.
RETURN SPRINGS FOR ROTARY SOLENOIDS
Cliftronics
standard rotary solenoids include clock type return springs
installed externally on the solenoid shaft. Standard spring
torque settings for each size rotary solenoid are listed
in our catalog. These springs are adjustable, normally to
± 30% of the nominal value. Other springs are also
available to provide higher or lower nominal torque values.
The standard spring torque tolerance is ± 20% from
nominal value.
22.
RETURN SPRINGS FOR HINGED CLAPPER SOLENOIDS
Standard
hinged clapper solenoids are supplied with a non-adjustable
internal return spring designed to counter-balance armature
weight and the armature hinge spring. Additional springs
and optional spring adjustment features are also available.
Consult our engineers to discuss your return spring requirements.
23.
RETURN SPRINGS FOR CLAPPER AND HOLDING SOLENOIDS
These
standard solenoids are not supplied with return springs.
Because of the small space typically available in these
low profile units, we recommend that external springs be
used whenever possible. In some cases, however, it may be
possible to design low profile springs for internal installation.
Our engineers are ready to help you with your return spring
requirements.
24.
RESPONSE TIME
The
response time, or "pull in time", of a solenoid
is the time, usually in milliseconds (ms), from the point
at which power is applied to the coil, until the plunger,
armature or shaft has reached the end of it's design stroke
or rotation.
Two
main events contribute to overall response time. One, (1)
is the time it takes for the current to overcome coil inductance
and develop the magnetic flux field required to generate
the required force. The other event, (2) is the time it
takes for the plunger or shaft to actually travel the stroke
distance. Flux field build-up normally takes more than half
of the total response time. This graph illustrates these
events.
Generally speaking, solenoid response times vary between
5 ms to 250 ms. Faster times are possible for small size
units with small armature mass and short strokes. Longer
times will be required for long stroke, larger size units.
To achieve
faster response times, the solenoids must be over-powered.
A solenoid size must be selected which will produce a force
at the start of the required stroke, which is several times
larger than would be required under normal speed operations.
Also, the stroke should be as short as possible to keep
the plunger or shaft travel time at a minimum. Special high-speed
designs are available. Please call our engineers for specific
information.
25.
DROP OUT TIME
Drop
Out Time, or "release time", is the time, normally
in milliseconds (ms), from the point where the power is
removed from the solenoid coil to the time the plunger or
shaft returns to it's normally de-energized position.
Two
main events contribute to the overall drop out time of a
solenoid. One is the time it takes the magnetic flux field
to collapse when the power is removed. The other event is
the time it takes for the plunger or shaft to actually travel
to its de-energized position as driven by gravity or spring
return.
Drop
out time can be increased by arc suppression diodes in the
solenoid circuit, by residual magnetism in the iron circuit
and by having closely matched or ground pole faces. Conversely,
drop out time can be reduced by removing diodes from solenoid
circuits and by inserting non-magnetic shims between the
pole faces to insure their separation.
26.
ANTI-RESIDUAL MAGNETISM STOPS
To
achieve the maximum holding, output forces and torques,
Cliftronics standard solenoids do not include any anti-residual
magnetism shims or stops. Such devices are often used to
provide a quicker drop out time. These shims, fabricated
from .002 to .010 thick stainless steel, brass or plastic,
keep the pole faces from meeting and effectively increase
the working air gap. While these shims usually do not change
the solenoid stroke, the greater air gap results in lower
working and holding forces. Our engineers will work with
you to determine if your application requires drop out shims
and what effect their use will have on the overall solenoid
performance.
27.
MOUNTING
Cliftronics
standard solenoids are provided with threaded mounting studs,
which are rugged and easily adaptable to most applications.
Standard lengths and tolerances are primarily determined
by the manufacturer of the threaded studs. However, custom
lengths can be provided to meet your application requirements.
Custom
mounting features may be necessary in some installations.
Our engineers will be happy to work with you to develop
the most functional and cost-effective mounting features
such as flanges or brackets for your application.
28.
DESIGN SERVICE LIFE
Standard
solenoid construction is normally designed and rated for
1,000,000 operating cycles. We are continually receiving
laboratory and field reports of cycle life exceeding the
standard design life. Actual cycle life will depend heavily
on the application use and environment. Periodic cleaning
and lubrication will help to extend solenoid life. Operating
conditions such as excessive side loads or inertial loads
on the armature or shaft may shorten solenoid life. Since
many factors, other than the solenoid construction itself,
have an effect on solenoid life, the rated solenoid life
expectancy is valid only for the laboratory conditions under
which the life tests were conducted. Our engineers will
be happy to discuss solenoid life cycle enhancing features
and options, such as special bearings, lubricants and heat
treatment that could enhance solenoid life expectancy.
29.
PROTOTYPE
Standard
solenoids can be assembled for prototype testing purposes
and for generating design ideas. We maintain a stock of
many common standard solenoids for prototype evaluation.
These units can normally be delivered very quickly. If the
prototype solenoids must be fabricated and assembled, delivery
may take a little longer. Testing the right unit the first
time may save you valuable time in the development time
cycle of your product. Our sales staff and engineers are
ready to work with you to get the best prototype solenoid
into your hands in the shortest possible time.
30.
STANDARD VS CUSTOM SOLENOIDS
Standard
solenoids will often meet the requirements of your application.
Standard solenoids can usually be produced with reduced
delivery times since we maintain an inventory of many of
the standard detail components.
Cliftronics
custom-engineered products are cost effective for production
volumes. Often, modifications to our standard solenoid components
will meet your application requirements. Delivery would
depend primarily on availability of any special components
or tooling. Cliftronics Sales and Applications Engineers
will guide you in making your selection of both standard
and custom features to best meet your form, fit and function
requirements.
We are
committed to our goals of:
- Continuous
Improvement
- Problem
Prevention
- Total
Customer Satisfaction
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