Reed Switches Technical, Appl Info

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REED SWITCHES ;, -~—~~—u-~ol~!~t
COTO TECHNOLOGY, INC.For most recent data visit www.cotorelay.com
REED
SWITCHES
Technical & Applications Information
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Standard packaging for uncut Reed Switches is a box containing
500 pieces. Standard packaging for SMD Reed Switches is Tape &
Reel. Special trays and/or Tape & Reel are available for some types.
Contact your local Coto Technology Representative with your special
packaging needs. Below is a chart of Tape & Reel dimensions for
standard products.
SWITCH TECHNICAL & APPLICATIONS INFORMATION
REED SWITCH PACKAGING
DIRECTION OF FEED
102MM
4.0"
330MM
13"
13MM
.512
2.72 MM
.107
D
B
D
C
EA
FIGURE 1
A
B
C
D
Fig. 1
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Series A B C D E Std. Qty/Reel
CT05 G1 2.57 10.92 8.00 24.00 2.59 2000
CT05 “J1 2.57 8.64 8.00 16.00 2.59 2000
CT10 A2, G1 2.68 16.90 8.00 32.00 3.30 2000
CT10 G2 3.00 19.80 8.00 32.00 3.12 2000
CT10 G4 3.00 19.80 8.00 32.00 3.12 2000
(Dimensions in Millimeters)
Recommended Pad Layouts for SMD Reed Relay Switches
Model Lead Type Fig. # Dim. A Dim. B Dim. C Dim. D
CT05 G1 1.424/10.76 .242/6.14 .091/2.31 .057/1.45
CT05 “J11.330/8.38 .168/4.27 .081/2.06 .057/1.45
CT10 A2 1.666/16.92 .529/13.44 .069/1.74 .050/1.27
CT10 G1 1.692/17.57 .520/13.20 .086/2.18 .041/1.04
CT10 G2 1.822/20.87 .640/16.25 .091/2.31 .057/1.45
CT10 G4 1.822/20.87 .640/16.25 .091/2.31 .057/1.45
(Dimensions in Inches/Millimeters)
08082017
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Dry-Reed Switch:
A dry-reed switch is an assembly containing
ferromagnetic contact blades, hermetically sealed in a glass envelope
and operated by an externally-generated magnetic field, e.g., that
from an actuating coil.
Operate Value:
The ampere turn value at which normally-open
contacts close. Lower value reflects higher sensitivity.
Operate Time:
The operate time is the time between the instant
of application of a magnetic field to a dry-reed switch and the instant
of the first physical closing of this switch. The operate time does not
include bounce time.
Release Value:
The ampere turn value at which normally-open
contacts, held closed by a magnetic field, will reopen as field strength
is reduced.
Release Time:
The release time is the time between the instant
of removal of an applied magnetic field to a dry-reed switch and the
instant of the first physical opening of this switch. The release time
does not include bounce time.
Bounce:
Bounce is a momentary opening of a switch after initial
closing, or a momentary closing after initial opening.
Bounce Time:
The bounce time is the interval of time between
the instant of initial closing (or opening) and the instant of final clos-
ing (or opening) of the dry-reed switch.
Dry-Reed Switch Contact Resistance:
The dry-reed switch
contact resistance is the resistance of the dry-reed switch under
specified conditions of measurement.
Saturate Value:
The saturate value is defined as the value of the
applied magnetic field at which the dry-reed switch is unaffected by
further increase of the applied magnetic field.
GLOSSARY OF TERMS
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Operate and Release Values
Operate and release values are dependent on the measuring coil, the
rate of energization (0.1 AT/ms), the detection of the operate (closing)
and the release (opening) moment, the position of the measuring
coil relative to the earths magnetic field and on the environmental
conditions.
Operate and Release Times
The operate and release times are dependent mostly on the energiza-
tion and de-energization rate. They are proportional to the R/L time
of the coil. Operate time is inversely proportional to the ratio of ener-
gization to operate value. Release time is proportional to the ratio of
energization to release value.
Bounce Time
The bounce time is almost independent of the energization, how-
ever, a high energization gives a somewhat shorter bounce time. The
bounce time is dependent on the current to be switched; above ap-
proximately 100 mA the bounce time is almost zero.
Contact Resistance
The contact resistance is dependent on the wire composition, wire
diameter, energization and contact layer. The published contact
resistance is measured with an open contact voltage of 20 mV and
a current through the closed contacts of 10 mA, using the 4-point
method (Kelvin method). Distance between measuring points for all
switch types is 41 mm.
Breakdown Voltage
The breakdown voltage depends on the gap between the contact
blades, kind of gas filling, gas pressure, material of the contact layer
and the availability of free electrons in the gas. The first three items
are set by the design of a particular reed switch. The last item is very
dependent on ambient conditions. Therefore minimum values are
given in the published data.
Insulation Resistance
The insulation resistance is dependent on the condition of the inside
of the glass envelope and on the environment, e.g. relative humidity,
conducting layers on the outside of the glass envelope.
Life Expectancy
The life of a dry-reed switch is influenced by the contact layer, the
mechanical characteristics of the reed switch blade, the load, the load
circuit parameters and the applied magnetic field. The contact layer
and the blade characteristics are determined by the manufacturer.
Load, load circuit parameters and magnetic field are determined by
the user. The load should be within the maximum published values.
The load circuit parameters (wiring capacitance and inductance),
should be kept as low as possible and the applied magnetic field must
be stronger than necessary for obtaining the maximum operate value.
Remark:
Due to the influence of the load circuit on contact
resistance and sticking, and also the influence of the applied
magnetic field and used coil or magnet, life-test information can
only be compared when it is the result of testing under exactly
the same conditions (test equipment).
Coils:
The electrical characteristics are measured using either the NARM1
coil or the 10JK coil. Using another coil may change these character-
istics. The measuring method e.g. speed, detection and the position
of the coil with respect to the earths magnetic field may also affect
the characteristics. The definitions of the NARM1 coil and the 10JK
coil are as follows:
10JK Coil: 10000 turns of 47 SWG single enameled copper wire
on an elliptical coil former of 12.5 mm winding length.
NARM 1 Coil: 5000 turns of 46 AWG single enameled copper
wire on an elliptical coil former of 10.4 mm winding length.
REED SWITCH CHARACTERISTICS
SWITCH TECHNICAL & APPLICATIONS INFORMATION
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Operation Using a Coil
Figures 2, 3 and 4 illustrate the various methods of operating the
switch using a coil.
With the method given in Fig. 4, the dry-reed switch and/or perma-
nent magnet can be placed either within or outside the coil.
REED SWITCH OPERATION METHODS
Fig. 3: A dry-reed switch mounted outside a coil
NS
lc
Fig.4: A dry-reed switch biased by a permanent magnet and operated by a coil
N
N
S
S
lc
Fig.2: A dry-reed switch mounted within a coil
NS
lc
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SWITCH TECHNICAL & APPLICATIONS INFORMATION
Operation Using a Permanent Magnet
Permanent magnets are also often used to operate dry-reed switches.
Figures 5, 6, 7 and 8 illustrate the various methods available.
REED SWITCH OPERATION METHODS
Fig. 6: Movement, with the magnetic field
perpendicular to the dry-reed switch
N
S
X
-Y +Y
OFF OFF
HOLD HOLD
-Y (mm) +Y (mm)
ON
OFF
Fig. 8: Rotational movement with two or more pole
ring magnets
N
N
S
N
N
S
S
SON
OFF
NS
N
S
N
S
N
S
Fig. 5: Movement, with the magnetic field parallel
to the dry-reed switch
NS
X
-Y +Y
OFF OFF
HOLD
-Y (mm) +Y (mm)
ON
Fig. 7: Rotational movement with a bar shaped
permanent magnet
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Shielding
Ferromagnetic materials which shunt the magnetic fields may be
used to shield a dry-reed switch (see Fig. 9).
Magnetic Application
There are many applications for dry-reed switches used in combina-
tion with a permanent magnet. Figure 10 shows the relationship
between the Gauss values of a permanent magnet and the AT values
of Coto dry-reed switches in the Philips Standard Coil. It enables the
customer to determine which reed switch AT range can be used in
combination with a specific permanent magnet.
REED SWITCH OPERATION METHODS
Fig. 9: Shielding a magnetically operated switch
NS
ON
SHIELD
OFF
Fig. 10: Relationship between the field strength of a
permanent magnet and the ampere-turn
values of Coto reed switches in the Philips
Standard Coil
1000 706010 20 30 40 50 9080
Philips Standard Coil (AT)
Permanent
Magnet
Field Strength
(Gauss)
250
200
225
150
175
100
125
50
75
25
0
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SWITCH TECHNICAL & APPLICATIONS INFORMATION
Application Information
Should your application require further information, please consult
your nearest Coto Technology sales office.
Contact Protection
Unless stated otherwise, the published life-expectancy data is based
on resistive loads. For inductive, capacitive or lamp loads, inrush
current or reverse voltage can affect the life of a reed switch. For a
maximum life-time, contact protection is advised.
Inductive Loads
To reduce the high reverse voltage produced when a reed switch
opens, the following contact protection can be applied:
DC voltage: a diode parallel to the load or
the reed switch (see Fig. 11).
AC voltage: An RC-network parallel to the load or
the reed switch (see Fig. 12).
and
where: C in μF; I in A; R in Ω; U in V.
Capacitive Loads
To reduce the high inrush current when a reed switch closes, a
resistor must be connected in series with the capacitance or the reed
switch.
When wiring a load and reed switch over a long distance, electrostat-
ic capacitance, arising from the cable, can damage the reed switch.
To protect against this capacitance a series surge protector (L) or a
resistor should be connected in series.
Lamp Loads
To reduce the high inrush current when a cold incandescent lamp
has to be switched by a reed switch (closing only), a resistor must be
connected in series with the lamp or parallel to the reed switch.
SWITCHING CONSIDERATIONS
C = 10
I2
R =
U
10 1 +
(50
U)
Fig. 11: DC voltage contact protection
+_
Fig. 12: AC voltage contact protection
~
R
C
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be happy to help you find that perfect small signal switching solution.
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