TRA294G/20-25 Cynergy3 Components, TRA294G/20-25 Datasheet - Page 9

• Manufacturer Part Number: TRA294G/20-25
• Description: Switch, Reed, NO, 10VA, 150V, .5A
• Manufacturer: Cynergy3 Components

Specifications of TRA294G/20-25

• Lead Free Status / Rohs Status: RoHS Compliant part

Reed Switch
Application Notes
The diagram illustrates a resistor/capacitor network for protecting a Reed
Switch against high inrush currents. R1 and/or R2 are used depending
upon circuit conditions.
Capacitive Loads
Unlike inductive loads, capacitive and lamp loads are prone to high inrush
currents which can lead to faulty operation and even contact welding. When
switching charged capacitors (including cable capacitance) a sudden
unloading can occur, the intensity of which is determined by the capacity and
length of the connecting leads to the switch. This inrush peak can be reduced
by a series of resistors. The value of these resistors is dependent on the
particular application but should be as high as possible to ensure that the
inrush current is within the allowable limits.
Cutting and Bending
As the Reed Switch blades form part of a magnetic circuit, shortening the
leads results in increased pull-in and drop-out values.
With lamp load applications it is important to note that cold lamp filaments
have a resistance 10 times smaller than already glowing filaments. This
means that when being turned-on, the lamp filament experiences a current
flow 10 times greater than when already hot. This high inrush current can
be reduced to an acceptable level through the use of a series of current-
limiting resistors. Another possibility is to fit a resistor across the switch.
This allows just enough current to flow through the filament to keep it warm,
yet not enough to make it glow.
Lamp load with parallel or current limiting resistor across the switch
V
40
30
20
10
0
Pull-in and drop-out sensitivity
Cut-off length in mm
RS
Lamp
2
V
R1
Example
R1 RS
4
R2
C
6
Cable
V
8
Load
RS
R2
Lamp
10
12
Rotation:
Examples of switching through rotational movement:
Indirect Actuation: Shielding
With the stationary arrangement of a Reed Switch and magnet, the reed
contacts are closed. Should the magnetic field be diverted away from the Reed
Switch by a shield of ferro-magnetic material placed between the switch and the
magnet, the contacts will open. When the shield is removed, the reed contacts
become magnetically actuated and close.
When cutting or bending Reed Switches, it is important that the glass body is not
damaged. Therefore, the cutting or bending point should be no closer than 3
mm to the glass body and the leads should be supported when cutting or
bending as shown.
Actuation of Reed Switches with a Permanent Magnet
Examples of switching with the use of a moving magnet
Direct Actuation:
A magnet moved perpendicularly towards
and away from a Reed Switch turns it on
and off once.
A magnet moved parallel to a Reed
Switch operates it from one to three
times.
A magnet swung towards and away from
a Reed Switch operates it once.
A ring magnet moved parallel to the
Reed Switches axis operates it from one
to three times.
closed
open
N
N
magnet
S
magnet
open
S
Bending
Cutting
closed
magnetic shield
magnet
closed
closed
closed
open
ring magnet
open
open
N
magnet
N
N
magnet
N
S
N
magnet
closed
S
S
S
S
closed
open
open
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