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Precautions for Use of
Resistors |
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Please refer to precautions for use in
the beginning part for particulars common to all product types. |
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Precautions
for Use of Fixed Resistors |
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Fixed resistors in general |
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When an ambient temperature exceeds a rated
ambient temperature, resistors shall be applied on the derating
curve by derating the load power. |
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General resistors are not combustion-resistant
and are likely to emit, flame, gas, smoke, red heat, etc. under
overloads. Flame retardant resistors generally emit smoke and red
heat in a certain power and over but do not emit fire or flame. |
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When resistors are shielded and coated with
resin etc., the storage heat might uncommonly degrade the resistors.
It is also conceivable that the resin composition affect the characteristics
of resistors, so performance and reliability of resistors should
be checked before use. |
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In case of resin coating/potting or molded sealing,
confirm sufficiently the evaluation of reliability and use those
that have small contractile stress at a resin stiffening time because
the protection coat may be peeled off, cracks may occur at the solder
connection, resistance values may be changed and disconnection may
occur by the stress at the resin stiffening time. Especially for
urethane sealing compounds, take care that they are apt to adsorb
humidity and to degrade resistance to humidity/corrosion. Regarding
incombustible coating products, no coating or sealing shall be done. |
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When a voltage higher than rated is applied
in a short time (single pulse, repeated pulses, surge, etc.), it
does not necessarily ensure safety that an effective wattage is
not higher than a rated wattage. Then consult with us with your
specified pulse wave shape. |
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Leaded type film resistors are spirally trimmed
and have inductance ingredients. When using them in high frequency
circuits, check them in advance on the actual machines. |
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Resistors shall be used in a condition causing
no dew condensation. |
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The materials for chip resistors are composed
of alumina. When heat stresses such as heat shock, etc. are repeatedly
applied, the solder at the connected section (solder fillet section)
can cause a crack because of the difference in thermal expansion
coefficient between the resistor and the mounting board. The design
should be made with much care, especially for a large type because
the occurrence of the crack is influenced by the size of a land
(pad), volume of solder, volume of radiation for a mounting board,
etc. |
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For basic particulars for cautions, refer to
EIAJ Technical Report RCR-2121A "Guidance for carenote on fixed
resistors". |
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Care should be taken to the fact that slipping
out of position during mounting may increase to cause solder bridges. |
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As chip networks receive mechanical stress easier
than chip resistors, take care so that no strong mechanical stress
is given during and after the mounting. |
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An incorrect solder volume increases stress
on resistors and may result in cracks or performance defects. Be
careful to avoid too much or too little soldered volume. |
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If impurity material by flux etc. is stuck on
this product or a mounted PCB, the resistor performance may be declined
considerably by water of dew condensation etc. attached to the products.
It is suggested that you confirm environmental and mounting conditions
before use. |
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Metal oxide film resistors |
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The special flame retardant coating for metal
oxide film resistors is less resistant against external shock than
that of for ordinary resistors. So, never give shocks or vibrations
on the resistors. Also never damage them by picking up the coated
films with pliers, tweezers, etc. |
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After cleaning, no external power should be
put on the coated films before they are well dried. |
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When being used in AC circuits, some wirewound
structures give inductance ingredients or parasitic capacity, so
they may cause unusual phenomena such as oscillations etc. Quorum
deviations of other components should be carefully taken into account
for use. |
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When using, it shall be made sure that the overload
conditions at unusual moments lie within the fusing territory. |
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Consult with us in advance when overloaded higher
than the rated voltage under an ordinary situation since such an
overload may store up damages on resistors. |
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Use at the maximum open-circuit voltage or lower
as an arc phenomenon may arise when high voltage is applied again
after fusing by an overcurrent. |
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Consult with us for the maximum open-circuit
voltage because it varies with type and resistance. |
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When coating/potting or molded sealing by resin,
storage heat may affect the fusing characteristics so confirm in
advance by the actual machines taking constants deviations of other
components into consideration. |
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Precautions
for Use of Trimmer Potentiometers |
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Trimmer Potentiometers in General |
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When an ambient temperature exceeds a rated
ambient temperature, resistors shall be applied on the derating
curve by derating the load power. |
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When using the component with partial load,
alleviate the rated power in proportion to the resistance ratio. |
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When soldering, take care that flux and solder
are not attached to other areas than terminations. The function
of the component will be damaged if they are attached to the surfaces
of resistor element or sliders. |
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C4000 series can be washed with organic solvents.
Ask us for the usability of the solvents to be used. |
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Leaded types SF6 and SF8 can not be washed with
organic solvents. |
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Do not force the resistance adjustment knob.
While the C4000 series do not have a revolution stopper, leaded
types SF6 and SF8 have a revolution stopper, so the stopper may
lose its function and then be destroyed if more force than necessary
is applied to both terminal positions. |
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Consult with us beforehand if the use of the
lock paint is required to fix the position for adjustment. When
it is used, see to it that the resin does not enter the inner contact
section etc. |
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If carbon trimmer potentiometers are used in
DC, they should be used with the resistor side as - and with the
slider side as + so that the DC, which is applied to the slider,
can avoid an abnormality in resistance that is caused by a phenomenon
of anodic oxidization at the contact section between the slider
and the resistor. |
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For basic precautions, refer to EIAJ Technical
Report RCR-2191A "Guideline of notabilia for potentiometers
for use in electronic equipment". |
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Application Notes
Brush up your circuit
Basic Knowledge
