Flameproof Metal
Oxide Resistors
WMO-S Series
Cost effective
Small size for power rating
Good pulse handling capability
Flameproof protection
Electrical Data
WMO½S
Power rating @70°C
Resistance range
Limiting element voltage
TCR (25 to 75°C)
Isolation Voltage
Resistance tolerance
Standard Values
Thermal Impedance
°C/watt
°C
125
105
Ambient temperature range
watts
ohms
volts
ppm/°C
volts
%
250
5
E24
75
-55 to +155
63
42
250
300
350
350
500
½
WMO1S
1
WMO2S
2
10R 100K
350
500
WMO3S
3
WMO5S
5
Physical Data
Dimensions (mm) and Weight (g)
Type
WMO½S
WMO1S
WMO2S
WMO3S
WMO5S
L max.
7.5
10
12
16
26
D max.
3
4.5
5
5.5
8.5
D
f min.
27
27
28
28
38
d nom.
0.6
0.7
0.7
0.8
0.8
PCB mounting centres
Min. bend radius
0.6
1.05
1.05
1.2
1.2
Wt. nom.
0.22
0.42
0.63
1.0
3.7
12.7
15.2
17.8
20.3
30.5
d
L
f
General Note
Welwyn Components reserves the right to make changes in product specification without notice or liability.
All information is subject to Welwyns own data and is considered accurate at time of going to print.
© Welwyn Components Limited
Bedlington Northumberland NE22 7AA, UK
Telephone: +44 (0) 1670 822181 Facsimile: +44 (0) 1670 829465 Email: info@welwyn-tt.com Website: www.welwyn-tt.com
A subsidiary of
TT electronics plc
Issue A . 11.06
WMO-S Series
Construction
The resistive film is deposited onto a high purity ceramic rod. End caps are force fitted and termination wires are welded to the end caps. The
element is adjusted to the required resistance value by a helical cut. Finally a cement protection is applied to the resistor body prior to marking
with indelible ink.
Marking
WMO-S resistors are colour coded with four bands indicating value and tolerance in accordance with IEC62.
Solvent Resistance
The body protection and marking are resistant to all normal industrial cleaning solvents suitable for printed circuits.
Flammability
The resistor coating will not burn under any condition of applied temperature or component overload.
Performance Data
Maximum
Load at Rated Power: 1000hrs @ 70°C
Short term (5s) overload
Derating
Temperature cycling
Moisture resistance
Resistance to solder heat
Insulation resistance
D
R%
D
R%
D
R%
D
R%
D
R%
G
W
5
2 + 0.05
W
See derating curve
2 + 0.05
W
5
1
>10
WMO-S Series Derating Curve
100
% of Rated Power at 70 ºC
45
0
70
155
235
Ambient temperature (ºC)
© Welwyn Components Limited
Bedlington Northumberland NE22 7AA, UK
Telephone: +44 (0) 1670 822181 Facsimile: +44 (0) 1670 829465 Email: info@welwyn-tt.com Website: www.welwyn-tt.com
Issue A . 11.06
WMO-S Series
Application Notes
1. If the resistors are to dissipate full rated power, it is recommended that the terminations should not be soldered closer than 4mm from the body.
2. Due to operating temperature limits imposed by some PCB materials, derating may be necessary. An estimate of the temperature
rise to be expected can be calculated using the thermal impedance figures given under Electrical Data.
3. WMO-S resistors can also be supplied with radial, goalpost or lancet pre-formed leads. Consult Factory for details.
Radial
Goalpost
Lanset
Packaging
Our standard packaging for WMO-S is taped and boxed. The critical dimensions are shown in Figure 1. The component wires will not protrude
beyond the outside edge of the tapes. Pre-formed resistors are supplied loose packed in plastic bags or boxes.
Dimensions mm
WMO½S
WMO1S
WMO2S
WMO3S
WMO5S
A
B
52
5
52
5
Figure 1
52
5
67
10
85
10
B
6
f
1
A
f
2
6
Body location f1-f2 < 1.4mm
Ordering Procedure
Specify type reference, value and tolerance as shown in this example of WMO3S at 1.5K
W
, 5%:
T ype
Value (use IE C62 code)
T olerance (use IE C 62 code)
J 5%
P acking Code
W MO 3 S 1 K 5 J A 1
A5
A1
A05
Ammo
Pack
WMO
1 2
S
WMO1S, WMO2S, WMO3S
WMO5S
5000 / Box
1000 / Box
500 / Box
© Welwyn Components Limited
Bedlington Northumberland NE22 7AA, UK
Telephone: +44 (0) 1670 822181 Facsimile: +44 (0) 1670 829465 Email: info@welwyn-tt.com Website: www.welwyn-tt.com
Issue A . 11.06
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