REED RELAYS
APPLICATION DATA
HOW REED RELAYS WORK
The term reed relay covers dry reed relays and mercury-
wetted contact relays, all of which use hermetically sealed
reed switches. In both types, the reeds (thin, flat blades)
serve multiple functions - as conductor, contacts, springs,
and magnetic armatures.
DRY REED RELAYS
Dry reed relays have become an important factor in the relay
field. They have the advantage of being hermetically sealed
and resistant to atmospheric contamination. They have fast
operate and release times and when operated within their
rated contact loads, have very long life. A typical dry reed
switch capsule is shown in Figure 1.
Latching switches are manufactured by using a SPST-NO
contact, and biasing it with a permanent magnetic that is
strong enough to hold the contacts closed, but not strong
enough to hold the contact closed when coil power is
applied to the coil. The switching process is than reversed
by simply reversing the relay coil polarity to close the
switch, or by employing a second coil with a reverse field.
MAGNETIC FIELDS
Reed relays in general can be characterized as susceptible
to the influences of external magnetic fields. It is important
to keep reed relays at a proper distance from each other
because of the possibility of magnetic-interaction between
them. Proper magnetic shielding must be used to contain
stray magnetic fields. When installing reed relays into
equipment, one should be aware of the devices within that
equipment which can produce magnetic fields. The relays
being installed into that equipment should be positioned as
far away as possible from any stray magnetic fields and
should be shielded to prevent false operations.
ELECTRICAL CHARACTERISTICS
SENSITIVITY: The input power required to operate dry reed
relays is determined by the sensitivity of the particular reed
switch used, by the number of switches operated by the
coil, by the permanent magnet biasing (if used), and the
efficiency of the coil and the effectiveness of its coupling
to the blades. Minimum input required to effect closure
ranges from the very low milliwatt level for a single
sensitive capsule to several watts for multipole relays.
OPERATE TIME: The coil time constant, overdrive on the
coil, and the characteristics of the reed switch determine
operate time. With the maximum overdrive voltage applied
to the coil, reed relays will operate in approximately the
200 microsecond range. When driven at rated coil voltage,
usually the relays will operate at about one millisecond.
RELEASE TIME: With the coil unsuppressed, dry reed
switch contacts release in a fraction of a millisecond.
SPST-NO contacts will open in as little as 50 microseconds.
Magnetically biased SPST-NC and SPDT switches reclose
from 100 microseconds to 1 millisecond respectively. If the
relay coil is suppressed, release times are increased.
Diode suppression can delay release times for several
milliseconds, depending on coil characteristics, coil
voltage, and reed release characteristics.
CONTACT BOUNCE
Dry reed contacts bounce on closure as with any other
hard contact relay.The duration of bounce on a Dry reed
switch is typically very short, and is in part dependent on
drive level. In some of the faster devices, the sum of the
operate time and bounce is relatively constant. As drive is
increased, the operate time decreases with bounce time
increasing. The normally closed contacts of a SPDT switch
bounce more then the normally open contacts.
Magnetically biased SPST-NC contacts exhibit essentially
the same bounce characteristics as SPST-NO switches.
SUPPORTING
TERMINAL
GLASS
CAPSULE
SUPPORTING
TERMINAL
NORMALLY OPEN CONTACTS
Figure 1. Construction of Switch Capsule
of Typical Dry Reed switch (SPST-NO)
In the basic SPST-NO design, two opposing blades are
sealed into a narrow glass capsule and overlapped at their
free ends. The contact area is plated typically with rhodium
to produce a low contact resistance when contacts are
drawn together. The capsule is made of glass and filled
with a dry inert gas and then sealed. The capsule is
surrounded by an electromagnetic coil. When the coil is
energized, the normally open contacts are brought together;
when the coil voltage is removed, the blades separate by
their own spring tension. Some reeds contain permanent
magnets for magnetic biasing to achieve normally closed
contacts (SPST-NC) or SPDT contact combinations. The
current rating, which is dependent upon the size of the blade
and the type and amount of plating, may range from low level
to 1 amp. Effective contact protection is essential when
switching loads other then dry resistive loads.
CONTACT COMBINATIONS.
The switches used in dry reed relays provide SPST-NO,
SPST-NC, SPDT contact combinations. The SPST-NO
corresponds with the basic switch capsule design (Fig.1).
The SPST-NC results from a combination of the SPST-NO
switch and a permanent magnet strong enough to pull the
contacts closed but able to open when coil voltage is applied
to the relay coil. In typical true SPDT designs, the armature
is mechanically tensioned against the normally closed contact,
and is moved to the normally open contact upon application
of a magnetic field. The SPDT contact combination can also
be achieved by joining a SPST-NO switch with an appropriately
adjusted SPST-NC switch, and jumping one side of both
switches together to form the movable contact system.
Latching contacts, defined as contacts which remain in the
position to which they were driven, and stay in that position
when coil power is removed from the relay coil.
9/04
6...
4
REED RELAYS
APPLICATION DATA
CONTACT RESISTANCE
The reeds (blades) in a dry reed switch are made of magnetic
material which has a high volume resistivity, terminal-to-
terminal resistance is somewhat higher than in some other
types of relays. Typical specification limits for initial resistance
of a SPST-NO reed relay is 0.200 ohms max (200 milliohms).
INSULATION RESISTANCE
A dry reed switch made in a properly controlled internal
atmosphere will have an insulation resistance of 10
12
to 10
13
ohms or greater. When it is assembled into a relay, parallel
insulation paths reduce this to typical values of 10
13
ohms.
Depending on the particular manner of relay construction,
exposure to high humidity or contaminating environments
can appreciably lower final insulation resistance.
CAPACITANCE
Reed capsules typically have low terminal-to-terminal
capacitance. However, in the typicall relay structure where
the switch is surrounded by a coil, capacitance from each
reed to the coil act to increase capacitance many times. If
the increased capacitance is objectionable, it can be reduced
by placing a grounded electrostatic shield between the switch
and coil.
DIELECTRIC WITHSTAND VOLTAGE
With the exception of the High-Voltage dry reed switches
(capsules that are pressurized or evacuated), the dielectric
strength limitation of relays is determined by the ampere
turn sensitivity of the switches used. A typical limit is 200
VAC. The dielectric withstand voltage between switch and
coil terminals is typically 500 VAC.
THERMAL EMF
Since thermally generated voltages result from thermal
gradients within the relay assembly, relays built to
minimize this effect often use sensitive switches to reduce
required coil power, and thermally conductive materials to
reduce temperature gradients. Latching relays, which may
be operated by a short duration pulse, are often used if the
operational rate is not changed for longer periods of time
because coil power is not required to keep the relay in the
on or off position after the initial turn on or turn off pulse.
NOISE
Noise is defined as a voltage appearing between terminals
of a switch for a few milliseconds following closure of the
contacts. It occurs because the reeds (blades) are moving
in a magnetic field and because voltages are produced within
them by magnetostrictive effects. From an application
standpoint, noise is important if the signal switched by the
reed is to be used within a few milliseconds immediately
following closure of the contacts. When noise is critical in
an application, a peak-to-peak limit must be established by
measurement techniques, including filters which must be
specified for that particular switching application.
ENVIRONMENTAL CHARACTERISTICS
Reed relays are used in essentially the same environments as
other types of relays. Factors influencing their ability to function
would be temperature extremes beyond specified limits
VIBRATION
The reed switch structure, with so few elements free to move,
has a better defined response to vibration than other relay
types. With vibration inputs reasonably separated from the
resonant frequency, the reed relay will withstand relatively high
inputs, 20 g's or more. At resonance of the reeds, the typical
device can fail at very low input levels. Typical resonance
frequency is 2000 hz.
SHOCK
Dry reed relays will withstand relatively high levels of shock.
SPST-NO contacts are usually rated to pass 30 to 50 g's,
11 milliseconds, half sign wave shock, without false
operation of contacts. Switches exposed to a magnetic
field that keep the contacts in a closed position, such as in the
biased latching form, demonstrate somewhat lower resistance
to shock. Normally closed contacts of mechanically biased
SPDT switches may also fail at lower shock levels.
TEMPERATURE
Differential expansion or contraction of reed switches and
materials used in relay assemblies can lead to fracture of
the switches. Reed relays are capable of withstanding
temperature cycling or temperature shock over a range of
at least -50C to + 100C. These limits should be applied to
the application to prevent switch failure.
CONTACT PROTECTION
Tungsten lamp, inductive and capacitive discharge load are
extremely detrimental to reed switches and reduce life
considerably. Illustrated below are typical suppression
circuits which are necessary for maximum contact life.
INPUT
R
Figure 3
Initial cold filament turn-on current is often 16 times higher
than the rated operating current of the lamp. A current limiting
resistor in series with the load, or a bleeder resistor across the
contacts will suppress the inrush current. The same circuits
can be used with capacitive loads, as shown in Figure 3.
INPUT
Figure 4
DC inductive loads call for either a diode or a thyristor to be
placed across the load. These circuits are necessary to protect
the contacts when inductive loads are to be switched in a
circuit, as shown in Figure 4.
9/04
INPUT
INPUT
R
6...
5
SIP & DIP
MINIATURE REED RELAYS
107DIP, 171DIP, 172DIP(SPDT)
14
DIMENSIONS SHOWN IN INCHES & (MILLIMETERS)
.
OUTLINE DIMENSIONS
117SIP
0.290 MAX.
(7.36)
1
0.300 MAX.
(7.62)
0.275 MAX.
(6.98)
0.020 TYP.
(0.51)
0.100 TYP.
(2.54)
0.750 MAX.
(19.0)
0.290 MAX.
(7.36)
0.075 TYP.
(1.90)
0.750 MAX.
(19.0)
0.110
(2.79)
0.260 MAX
(6.60)
0.010 TYP.
(0.25)
PIN NO.1
INDICATOR
0.010 TYP.
(0.25)
0.400
(10.1)
0.020 TYP.
(0.51)
0.600 TYP
(15.2)
0.020 TYP.
(0.51)
0.150 TYP.
(3.81)
0.200 TYP.
(5.08)
0.600 TYP.
(15.2)
0.030 TYP.
(0.762)
0.140TYP.
(3.55)
172DIP (DPDT)
GENER AL SPECIFICATIONS (@ 25
ºC
)
COIL
Pull-in Voltage AC (50/60 Hz):<
Pull-in Voltage DC:<
Dropout Voltage AC (50/60 Hz):>
Dropout Voltage DC:>
Maximum Voltage:
Resistance:
Coil Power AC (60 Hz):
Coil Power DC:
CONTACTS
Contact Material:
Contact Rating AC Amperes (AC1):
Contact Rating AC Voltage:
Contact Rating DC Amperes (DC1):
Contact Rating DC Voltage:
Contact Rating :
General Purpose Rating (75%-80%):
Horse Power (AC):
Pilot Duty (60 Hz):
VA Rating Make:
VA Rating Break:
Minimum Recommended Load:
TIMING
Operate Time:
Release Time:
DIELECTRIC S TRENGTH
Coil to Contacts:
Across Open Contacts:
Pole to Pole:
Contacts to Frame:
Insulation Resistance:
VIBR ATION RESIS TANCE
Functional:
9/04
UNITS
% of nominal
Not applicable
% of nominal
80
% of nominal
Not applicable
% of nominal
10
% of nominal
110
%±
10
VA
Not applicable
W
117SIP, 107DIP: 0.050 to 0.288
171DIP: 0.050 to 0.270
172DIP: 0125 to 0.540
A
V
A
V
VA
HP
VA
VA
ma
ms
ms
V rms
V rms
V rms
V rms
megohms
minimum
@VDC
gs
RHODIUM
117SIP, 107DIP, 171DIP: 0.5
172 DIP: 0.25
117SIP, 107DIP: 120
171DIP, 172 DIP: 60
0.5
100
117SIP, 107DIP, 171DIP:
10
172 DIP: SPDT 4, DPDT 10
Not applicable
Not applicable
Not applicable
Not applicable
Not applicable
10 or 0.05 Watt
1
1
500
150
Not applicable
Not applicable
1000 @ 500
PIN NO.1
LOCATION
0.800 MAX.
(20.32)
0.400 MAX.
(10.16)
0.400 MAX.
(10.16)
0.025
(0.635)
0.100 TYP.
(2.54)
0.600 TYP.
(15.2)
0.082 TYP.
(2.09)
SHOCK RESIS TANCE
Functional:
TEMPER ATURE
Operating, AC Lower:
Operating, AC Upper:
Operating, DC Lower:
Operating, DC Upper:
Storage, Lower:
Storage, Upper:
LIFE EXPECTANCY
Electrical @ Rated Load (AC1):
Mechanical @ no Load :
MISCELLANEOUS
Operating Position:
Insulation Material:
Enclosure Material:
Cover Protection Category:
Weight:
0.125 TYP.
(3.17)
0.046 TYP.
(1.19)
0.3 ±0.003
(7.62)
UNITS
gs
ºC
ºC
ºC
ºC
ºC
ºC
operations
operations
50
Not applicable
Not applicable
-40
+85
-40
+105
50,000,000
100,000,000
Any
Glass
Thermo set plastic
67
1
20
IP
grams
6...
6
PHONE: (843) 393-5778 FAX: (843) 393-4123 EMAIL: info@magnecraft.com
SIP & DIP
MINIATURE REED RELAYS
SPST NO OR NC, DPST NO, 0.5 AMP
COIL MEASURED
@
25
º
C
STANDARD
PART
NUMBERS
NOMINAL
INPUT
VOLTAGE
5
12
24
5
12
24
NOMINAL
RESISTANCE
(OHMS)
500
W
1000
W
2000
W
500
W
1200
W
2200
W
NOMINAL
POWER
(mW)
50
144
288
50
120
270
WIRING DIAGRAM
(TOP VIEWED )
SPST - N. O., 0.5 AMP
117SIP
W117SIP-1
W117SIP-3
W117SIP-5
SPST - N. C., 0.5 AMP
W117SIP-22
W117SIP-23
W117SIP-24
SPST - NO
SPST - NC
1
3
5
7
1
3
5
7
SPST - N. O. WITH CLAMPING DIODE, 0.5 AMP
W117SIP-6
5
500
W
W117SIP-8
12
1000
W
W117SIP-10
24
2000
W
SPST - N. C. WITH CLAMPING DIODE, 0.5 AMP
W117SIP-18
5
500
W
W117SIP-25
12
1200
W
W117SIP-26
24
2200
W
SPST - N. O., 0.5 AMP
50
144
288
50
120
220
SPST - NO
WITH DIODE
SPST - NC
WITH DIODE
1
3+
5-
7
1
3+
5-
7
SPST - NO
50
144
288
50
144
288
14
13
9
8
14
SPST - NO
13
9
107DIP
W107DIP-1
5
500 ½
W107DIP-3
12
1000
W
W107DIP-4
24
2000
W
SPST - N. O. WITH CLAMPING DIODE, 0.5 AMP
W107DIP-5
W107DIP-7
W107DIP-8
SPST - N. O., 0.5 AMP
W171DIP-2
5
500
W
W171DIP-4
12
1200
W
W171DIP-5
24
2200
W
SPST - N. O. WITH CLAMPING DIODE, 0.5 AMP
W171DIP-7
W171DIP-9
W171DIP-10
SPST - N. C., 0.5 AMP
W171DIP-12
5
200
W
W171DIP-14
12
1200
W
W171DIP-15
24
2200
W
SPST - N. C. WITH CLAMPING DIODE, 0.5 AMP
W171DIP-17
W171DIP-19
W171DIP-20
5
12
24
500
W
1200
W
2200
W
5
12
24
500
W
1000
W
2200
W
5
12
24
500
W
1000
W
2000
W
WITH DIODE
8
1
2
6
7
1
+2
6
7
SPST - NO
50
120
270
50
144
270
14
13
9
8
14
SPST - NO
13
9
WITH DIODE
8
1
2
6
7
1
+2
6
7
SPST - NC
50
120
270
50
120
270
14
13
9
8
14
SPST - NC
13
9
WITH DIODE
8
171DIP
WHEN SPACING SIP
RELAYS, THE RELAYS
REQUIRE 1/2 INCH
SPACING FROM THE
SIDE OF THE
ADJACENT RELAYS.
1
2
6
7
1 + 2
6
7
DPST - N. O., 0.5 AMP
W171DIP-21
5
500
W
W171DIP-23
12
1000
W
W171DIP-24
24
2200
W
DPST - N. O. WITH CLAMPING DIODE, 0.5 AMP
W171DIP-25
W171DIP-27
W171DIP-28
5
12
24
500
W
1000
W
2200
W
DPST - NO
50
144
270
50
144
270
14
13
9
8
14
DPST - NO
WITH DIODE
13
9
8
1
2
6
7
1
+2
6
7
9/04
PHONE: (843) 393-5778 FAX: (843) 393-4123 EMAIL: info@magnecraft.com
SEE END OF SECTION 6 FOR CROSS REFERENCE
6...
7
DIP
MINIATURE REED RELAYS
SPDT NO, DPDT, 0.25 AMP
COIL MEASURED
@
25
º
C
STANDARD
PART
NUMBERS
SPDT, 0.25 AMP
200
W
W172DIP-1
5
500
W
W172DIP-3
12
2200
W
W172DIP-4
24
SPDT WITH CLAMPING DIODE, 0.25 AMP
200
W
W172DIP-5
5
500
W
W172DIP-7
12
2200
W
W172DIP-8
24
125
300
270
125
300
270
NOMINAL
INPUT
VOLTAGE
NOMINAL
RESISTANCE
(OHMS)
NOMINAL
POWER
(mW)
WIRING DIAGRAM
(TOP VIEWED )
SPDT
14
13
9
8
SPDT
14
13
WITH DIODE
9
8
172DIP
1
2
6
7
1 + 2
6
7
SPDT, 0.25 AMP
200
W
W172DIP-31
5
500
W
W172DIP-33
12
2200
W
W172DIP-34
24
SPDT WITH CLAMPING DIODE, 0.25 AMP
200
W
W172DIP-35
5
500
W
W172DIP-37
12
2200
W
W172DIP-38
24
125
290
270
125
290
270
SPDT
14
13
9
8
14
SPDT
WITH DIODE
13
9
8
1
2
6
7
1
+2
6
7
SPDT, 0.25 AMP
200
W
W172DIP-141
5
1000
W
W172DIP-145
12
3200
W
W172DIP-146
24
SPDT WITH CLAMPING DIODE, 0.25 AMP
200
W
W172DIP-147
5
1000
W
W172DIP-149
12
3200
W
W172DIP-150
24
125
144
180
125
144
180
SPDT
14
13
9
8
SPDT
14
13
WITH DIODE
9
8
1
2
6
7
1
+2
6
7
DPDT
DPDT, 0.25 AMP
46
W
W172DIP-17
5
266
W
W172DIP-19
12
1066
W
W172DIP-20
24
DPDT WITH CLAMPING DIODE, 0.25 AMP
46W
W172DIP-21
5
266
W
W172DIP-23
12
1066
W
W172DIP-24
24
540
540
540
540
540
540
14
13
9
8
DPDT
14
13
WITH DIODE
9
8
172DIP
1
2
6
7
1 +2
6
7
SEE END OF SECTION 6 FOR CROSS REFERENCE
WHEN SPACING DIP RELAYS, THE RELAYS
REQUIRE 1/2 INCH SPACING FROM THE SIDE
OF THE ADJACENT RELAYS.
9/04
6...
8
PHONE: (843) 393-5778 FAX: (843) 393-4123 EMAIL: info@magnecraft.com
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