Fusible Metal Film
Resistors
FM Series
Welwyn Components
•
Predictable fusing characteristics
•
Flameproof protection
Electrical Data
FM
1
/
4
Power rating at 70˚ C
Resistance range
Limiting element voltage
TCR
Resistance tolerance
Standard values
Thermal impedance
Ambient temperature range
˚ C/watt
˚C
150
watts
ohms
volts
ppm/˚ C
%
0.25
0R1 - 10K
250
FM
1
/
2
0.5
0R1 - 27K
350
250
5
E24 preferred
120
-55 to 155
100
FM1
1.0
0R2 - 1K5
350
Physical Data
Dimensions (mm) & Weight (g)
PCB
Type
FM
1
/
4
FM
1
/
2
FM1
L max
6.2
9.0
12.5
D max
2.5
2.3
3.4
4.2
f min
21.0
19.6
17.8
d nom
0.6
0.8
0.8
mounting
centres
10.2
12.7
18.4
Min.
bend
radius
0.6
1.2
1.2
Wt. nom
0.3
0.6
0.9
d
D
L
f
Construction
The metal film is deposited on a high purity ceramic rod. End
caps are force fitted and termination wires welded to the
caps. The resistive film is adjusted to the required value by a
special helical cut; finally the cement protection is applied to
the resistor body and marked with indelible ink.
Marking
Resistors are colour coded with five bands. Four of the bands
are used to indicate value and tolerance, with IEC 62 colours
being used. A fifth yellow band denotes constant voltage
fusibility.
Solvent Resistance
Terminations
Material
Strength
Solder-coated copper wire.
The terminations meet the requirements of
IEC 68.2.21.
The body protection and marking are resistant to all normal
industrial cleaning solvents suitable for printed circuits.
Flammability
The resistors will not burn or emit incandescent particles
under any condition of applied temperature or power
overload.
Solderability
The terminations meet the requirements of
IEC 115-1, Clause 4.17.3.2.
General Note
Welwyn Components reserves the right to make changes in product specification without notice or liability.
All information is subject to Welwyn’s own data and is considered accurate at time of going to print.
A subsidiary of
TT electronics plc
Issue C · 03.02
B 01.07
© 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
164
Fusible Metal Film
Resistors
FM Series
Welwyn Components
Performance Data
Maximum
Load: 1000 hours at 70˚C
Shelf life: 12 months at room temperature
Derating from rated power at 70˚ C
Temperature rapid change
Resistance to solder heat
R%
R%
R%
R%
3
2
zero at 155˚ C
0.5
0.5
FM1 Fuse Times
FM
1
/
2
Fuse Times
Pulse Time (seconds)
Pulse Time (seconds)
Initial Power (W)
Initial Power (W)
Packaging
All resistors are supplied tape packed ready for loading on
to automatic sequencing and insertion machines.
The standard taping method and critical dimensions are
shown in figure 1. Component wire will not protrude
beyond the outside edge of the tapes.
Lead Formed resistors can also be supplied. Standard
options of Lancet, Radial and Goalpost forming are shown
in Lead Form Information section.
A detailed Packaging Data Sheet is available on request.
Figure 1
Pulse Time (seconds)
FM
1
/
4
Fuse Times
Initial Power (W)
Fusing
After fusing the final resistance value will be 50 times the
initial value.
5
f
1
6
52
Body Location f
1
– f
2
f
2
6
1.4 mm
Standard Quantities Per Package
Type
Large ammo pack
FM
1
/
4
5000
FM
1
/
2
2500
FM1
1500
© 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
B 01.07
Issue C · 03.02
165
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