Mini Melf
Resistors
WRM Series
Welwyn Components
•
High reliability
•
Predictable pulse handling capability
•
Tolerances down to 0.1%
•
TCR down to 5 ppm/°C
Electrical Data
WRM 0102
Power rating at 70°C
Resistance range
Limiting element voltage
TCR
Resistance tolerance
Standard values
Thermal impedance
Ambient temperature range
Insulation resistance
k/W
°C
ohms
250
watts
ohms
volts
ppm/°C
%
0.2
R22 – 2M21
150
15, 25, 50
WRM 0204
0.25
R22 – 10M
200
5, 15, 25, 50
0.1, 0.25, 0.5, 1.0
E24 & E96
200
-55 to +125
>10
10
140
WRM 0207
0.4
R22 – 8M2
300
25, 50
Physical Data
Dimensions (mm) and weight (g)
Type
WRM 0102
WRM 0204
WRM 0207
L
max
2.2
3.6
5.8
L
1
min
1.2
1.8
2.8
D
max
1.1
1.4
2.2
D
1
max
1.1
1.4
2.2
D
1
min
1.06
1.25
2.0
K
max
0.45
0.85
1.4
K
min
0.35
0.5
1.1
Weight
t per unit
0.01
0.02
0.08
L
D
1
L
1
K
D
Construction
A metal film is deposited onto a high dissipation ceramic
former to which solder plated teminating caps are fitted.
The resistor is adjusted to value by a helical cut in the film
and the body is protected by a lacquer coating.
Terminations
Material
Plated steel cap.
Solderability
The terminal caps have a multi-layer coating
of nickel-copper-nickel and pure tin. The pure
tin finish produces ageing free contacts on
which low melting solders can be used.
Dipped area shall be covered with a smooth
and bright solder coating after 3 seconds
immersion at 215°C.
Marking
Resistance values are colour coded with 5 bands.
The TCR is also colour coded as detailed below.
TCR 50 ppm – No Dot
TCR 25 ppm – Yellow Dot
TCR 15 ppm – Orange Dot
Solvent Resistance
The body protection and marking are resistant to all normal
industrial cleaning solvents suitable for printed circuit boards.
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 · 04.03
© 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
39
Mini Melf
Resistors
WRM Series
Welwyn Components
TCR and Tolerance Range
Type
Reference
5%
WRM0102
WRM0102
WRM0102
WRM0102
WRM0102
WRM0204
WRM0204
WRM0204
WRM0204
WRM0204
WRM0207
WRM0207
WRM0207
WRM0207
WRM0207
±50ppm
±25ppm
±15ppm
±10ppm
±05ppm
±50ppm
±25ppm
±15ppm
±10ppm
±05ppm
±50ppm
±25ppm
±15ppm
±10ppm
±05ppm
R22 – R91
–
–
–
–
R22 – R91
–
–
–
–
R22 – R91
–
–
–
–
2%
IRO – 9R1
–
–
–
–
–
–
–
–
–
–
–
–
–
–
TCR
Tolerance
Professional
1.0%
10R – 2.21M
10R – 221K
–
–
–
1R – 10M
10R – 475K
–
–
–
1R – 8.2M
–
–
–
–
0.5%
47RS – 221K
47R5 – 221K
100R – 100K
–
–
10R – 475K
10R – 475K
10R – 221K
–
–
10R – 1M
10R – 1M
–
–
–
Tolerance
Precision
0.25%
100R – 221K
100R – 221K
100R – 100K
–
–
22R – 332K
22R – 332K
22R – 221K
22R – 221K
100R – 100K
–
–
–
–
–
0.1%
–
100R – 100K
100R – 100K
–
–
43R – 332K
43R – 332K
43R – 221K
43R – 221K
100R – 100K
–
–
–
–
–
* TC 10ppm & 5ppm is specified over the temperature range -10°C to +85°C.
Performance Data
Test
Description
0.25
75
Ω
– <100 kΩ
Short time overload*
Bending test*
Resistance to soldering heat
Temperature rapid change
Endurance*
Load life
Climatic sequence*
Damp heat steady state*
Current noise
Solderability
Voltage coefficient
Voltage proof
1000h
8000 h
≤
0.25% + 0.05
Ω
≤
0.5% + 0.05
Ω
≤
0.25% + 0.05
Ω
≤
0.25% + 0.05
Ω
< 0.05 µV/V
≤
0.25% + 0.05
Ω
≤
0.5% + 0.05
Ω
≤
0.5% + 0.05
Ω
≤
0.5% + 0.05
Ω
< 0.25 µV/V
Dipped area shall be covered with a smooth
and bright solder coating of at least 96%
< 0.5 . 10
6
/V
No flashover or breakdown
≤
0.5% + 0.05
Ω
≤
1.0% + 0.05
Ω
≤
1.0% + 0.05
Ω
≤
1.0% + 0.05
Ω
< 3 µV/V
≤
0.05% + 0.01
Ω
≤
0.05% + 0.01
Ω
≤
0.05% + 0.01
Ω
≤
0.05% + 0.01
Ω
Results
∆
R/R ±
Stability class
0.5
10
Ω
– <75
Ω
>100 kΩ – 332 kΩ
≤
0.1% + 0.01
Ω
≤
0.1% + 0.01
Ω
≤
0.1% + 0.01
Ω
≤
0.1% + 0.01
Ω
1.0
0.22
Ω
– <10
Ω
>332 kΩ – 10 MΩ
≤
0.25% + 0.05
Ω
≤
0.25% + 0.05
Ω
≤
0.25% + 0.05
Ω
≤
0.25% + 0.05
Ω
* Resistors to be mounted on a PC-board according to IEC 115-1, clause 4.27.1
© 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
40
Issue C · 04.03
Mini Melf
Resistors
WRM Series
Welwyn Components
Pulse Handling Information
The permissible pulse load is determined by the resistance
change as given for the endurance test after 8000 hours.
1 Pulse Voltage Limit
V
max
The maximum permissible impulse voltage Vmax is the
voltage pulse short overload depending on the impulse time
t
i
. High ohmic values are protected by the interdependence of
voltage limit and impulse time. This function is given by the
equation.
V
max
2,5 .
V
max
=
+
V
max
1 +
t
i
. K
That means:
R
nominal resistance values
t
p
time of the pulse period (t
-1
= pulse frequency)
p
V
(t)
pulse voltage
V
peak voltage of the pulse
P
rated dissipation of the resistor at ambient
t
2
- t
1
temperature
impulse time
t
i
3 Continuous and Single Pulse Load
There is a difference between repetitive pulse load
(P
=
t
i
.
P
, with = power at the pulse time
t
i
)
t
p
~
V
max
= maximum permissible continuous voltage,
t
i
= pulse time and K = 100 s
-1
.
or single pulse load (eg switching events
P
-> 0).
A higher pulse load
P
max
is accepted in the latter case.
2 Maximum Pulse Load
The average load
P
must not exceed the rated dissipation. For
P
resistance values above the critical resistance the rated
dissipation is given by the resistance value and the limiting
element voltage
V
max
. It is required
P
= 1
t
p
.
R
t
2
t
1
4 Pulse Shapes
The diagrams show the maximum pulse load for a rectangular
pulse shape.
t
.
V
2
P
=
i
.
t
p
R
Other pulses should be converted into rectangular pulse
shape, having the same energy at given peak voltage.
For exponential pulses the calculation follows:
P
=
with
e
2
.
V
2 .
t
p
R
e
V
2
(t) dt
≤
P
=
R
.
C
or
e
=
L
R
V
t
i
V
t
i
e
0,37 .
V
t
1
t
2
Rectangular Pulses
t
Exponential Pulse
t
© 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 C · 04.03
41
Mini Melf
Resistors
WRM Series
Single Pulse
Maximum Pulse Load
Welwyn Components
100
Pulse Load
P
max
W
WRM 0102
WRM 0204
WRM 0207
10
1
0,1
10
µs
100
µs
1 ms
10 ms
100 ms
1s
10 s
Pulse Duration
t
i
Continuous Pulses
Maximum Pulse Load
Continuous Pulse Load
P
max
100
W
10
WRM 0102
WRM 0204
WRM 0207
1
0,1
10
µs
100
µs
1 ms
10 ms
100 ms
1s
10 s
Pulse Duration
t
i
Packaging
The WRM 0102 and 0204 resistors are supplied reeled on
8mm blister tape. WRM 0207 resistors are supplied on 12mm
blister tape.
Packaging complies with the requirements of IEC 286-3.
Bulk packaging is also available on request.
© 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
42
Issue C · 04.03
