Technical Terminology & Cautions for Use
OPERATING CHARACTERISTIC
■ Definition of operating characteristic
The main terminological illustrations and
meanings which are used with snap-
action switches are as follows.
Varying
display
method
Classification Terminology Symbol
Unit
N
Starting current
The force required to cause contact snap-action. It
is expressed terms of force applied to the the
actuator.
Operating
Force
OF
RF
Max.
Min.
RF
OF
The force to be applied to the the actuator at the
moment contact snaps back from operated
position to total travel position.
PT
TF
Force
Release
Force
TT
N
N
FP
OT
MD
Totaltravel
Force
Force applied to an actuator required to move from
an operating position to a total travel position
OP
RP
TF
PT
TTP
mm,
degree
Distance or agree of the actuator movement from
free position to operating position.
Pretravel
Max.
Min.
Max.
The distance or degree which the actuator is
permitted to travel after actuation without any
damage to the switching mechanism.
mm,
degree
Overtravel
OT
Movement
Movement
Differential
mm,
degree
The distance or degree from operating position to
release position of the actuator.
MD
TT
mm,
degree
The migration length or the move angle from the
free position to total travel position of actuator
Totaltravel
Center of mounting holes
Free
Position
mm,
degree
Position of the actuator when no force is applied
to.
FP
OP
Operating
Position
mm,
degree
The position of the actuator when the traveling
contacts snaps with the fixed contact.
Position
The position of the actuator when the traveling
contact snaps back from operating position to its
original position.
Release
Position
mm,
degree
RP
Total travel
Position
mm,
degree
The stopping position of the actuator after total
travel.
TTP
TECHNICAL NOTES ON MECHANICAL CHARACTERISTICS
■ Actuation Force and Stroke
■ Changes in Operating Characteristics
Adequate stroke setting is the key to high reliability. It is also
important that adequate contact force be ’maintained to ensure
high reliability. For a normally closed (NC) circuit, the driving
mechanism should be set so that the actuator is normally in the
free position. For a normally open (NO) circuit, the actuator
should be pressed to 70% to 100% of the specified stroke to
absorb possible errors.
Exercise design care so that malfunctions will not occur if the
operating characteristics vary by as much as 20% from, rated
values.
<Example>
In the OF max. 0.98N specification for FS snap-action switches,
the allowable max. is 0.98 N × (100%+20%) = 1.18 N
In the RF min. 0.15 N min. specification
If the stroke is set too close to the operating point (OP), this may
cause unstable contact, and in the worst case may cause
actuator damage due to inertia of the drive mechanism. It is
advisable that the stroke be adjusted with the mounting plate or
driving mechanism.
the allowable min. 0.15 N × (100%–20%) = 0.12 N
■ Mechanical Conditions for Type Selection
Actuator type should be selected according to activation
method, activation speed, activation rate, and activation
frequency.
The figure at right
shows a typical
example of activation
1) An extremely slow activation speed may cause unstable
contact transfer, possibly resulting in contact failures or contact
fusion.
OF
and contact forces
varying with stroke.
2) An extremely high activation speed may cause damage to
contacts or contact response failure.
RF
In the vicinity of the
OP and RP, the
FP
RP
TTP
OP
Stroke
■ Driving Mechanism
MD
PT
OT
contact force is
Use of a driving mechanism which will cause physical impact to
diminished, causing
chatter and contact
bounce immediately
before or after
reversal. For this
reason, use the
the actuator should be avoided.
NC
On FP
<Example>
On reversal
Stroke
On reversal
On OTP
NO
switch while giving
due consideration to
this.This also causes
the snap action
Bad
Good
switch to be sensitive
to vibration or shock.
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