Technical Terminology & Cautions for Use

–2–

AECTB36E 201510-T

OPERATING CHARACTERISTIC

TECHNICAL NOTES ON MECHANICAL CHARACTERISTICS

■ Definition of operating characteristic

The main terminological illustrations and

meanings which are used with snap-

action switches are as follows.

Center of mounting holes

FP

OF

RF

TT

MD

OT

TTP

OP

PT

TF

RP

Classification

Terminology

Symbol

Unit

Varying

display

method

Starting current

Force

Operating

Force

OF

N

Max.

The force required to cause contact snap-action. It

is expressed terms of force applied to the the

actuator.

Release

Force

RF

N

Min.

The force to be applied to the the actuator at the

moment contact snaps back from operated

position to total travel position.

Totaltravel

Force

TF

N

Force applied to an actuator required to move from

an operating position to a total travel position

Movement

Pretravel

PT

mm,

degree

Max.

Distance or agree of the actuator movement from

free position to operating position.

Overtravel

OT

mm,

degree

Min.

The distance or degree which the actuator is

permitted to travel after actuation without any

damage to the switching mechanism.

Movement

Differential

MD

mm,

degree

Max.

The distance or degree from operating position to

release position of the actuator.

Totaltravel

TT

mm,

degree

The migration length or the move angle from the

free position to total travel position of actuator

Position

Free

Position

FP

mm,

degree

Position of the actuator when no force is applied

to.

Operating

Position

OP

mm,

degree

±

The position of the actuator when the traveling

contacts snaps with the fixed contact.

Release

Position

RP

mm,

degree

The position of the actuator when the traveling

contact snaps back from operating position to its

original position.

Total travel

Position

TTP

mm,

degree

The stopping position of the actuator after total

travel.

■ Actuation Force and Stroke

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.

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 figure at right

shows a typical

example of activation

and contact forces

varying with stroke.

In the vicinity of the

OP and RP, the

contact force is

diminished, causing

chatter and contact

bounce immediately

before or after

reversal. For this

reason, use the

switch while giving

due consideration to

this. This also causes

the snap action

switch to be sensitive

to vibration or shock.

■ Changes in Operating Characteristics

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

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.

1) An extremely slow activation speed may cause unstable

contact transfer, possibly resulting in contact failures or contact

fusion.

2) An extremely high activation speed may cause damage to

contacts or contact response failure.

■ Driving Mechanism

Use of a driving mechanism which will cause physical impact to

the actuator should be avoided.

<Example>

Bad

Good

OF

RF

PT

NC

On FP

On reversal

On reversal

On OTP

NO

Stroke

Stroke

MD

OT

FP

RP

OP

TTP