Mini Melf
Resistors
WRM Series
•High reliability
•Predictable pulse handling capability
•Tolerances down to 0.1%
•TCR down to 5 ppm/°C
Dimensions (mm) and weight (g)
Type L L1DD
1D1K K Weight
max min max max min max min
t per unit
WRM 0102 2.2 1.2 1.1 1.1 1.06 0.45 0.35 0.01
WRM 0204 3.6 1.8 1.4 1.4 1.25 0.85 0.5 0.02
WRM 0207 5.8 2.8 2.2 2.2 2.0 1.4 1.1 0.08
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.
© 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
WRM 0102 WRM 0204 WRM 0207
Power rating at 70°C watts 0.2 0.25 0.4
Resistance range ohms R22 – 2M21 R22 – 10M R22 – 8M2
Limiting element voltage volts 150 200 300
TCR ppm/°C 15, 25, 50 5, 15, 25, 50 25, 50
Resistance tolerance % 0.1, 0.25, 0.5, 1.0
Standard values E24 & E96
Thermal impedance k/W 250 200 140
Ambient temperature range °C -55 to +125
Insulation resistance ohms >1010
Electrical Data
Physical Data
Issue C · 04.03
A subsidiary of
TT electronics plc
Welwyn Components
39
L
K
L1
D
D1
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.
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
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.
Solvent Resistance
The body protection and marking are resistant to all normal
industrial cleaning solvents suitable for printed circuit boards.
WRM_C.qxd 28/4/03 10:02 am Page 1
Mini Melf
Resistors
WRM Series
© 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
Welwyn Components
TCR and Tolerance Range
* TC 10ppm & 5ppm is specified over the temperature range -10°C to +85°C.
* Resistors to be mounted on a PC-board according to IEC 115-1, clause 4.27.1
Performance Data
Type TCR Tolerance Tolerance
Reference Professional Precision
5% 2% 1.0% 0.5% 0.25% 0.1%
WRM0102 ±50ppm R22 – R91 IRO – 9R1 10R – 2.21M 47RS – 221K 100R – 221K –
WRM0102 ±25ppm – – 10R – 221K 47R5 – 221K 100R – 221K 100R – 100K
WRM0102 ±15ppm – – – 100R – 100K 100R – 100K 100R – 100K
WRM0102 ±10ppm – –––––
WRM0102 ±05ppm – –––––
WRM0204 ±50ppm R22 – R91 – 1R – 10M 10R – 475K 22R – 332K 43R – 332K
WRM0204 ±25ppm – – 10R – 475K 10R – 475K 22R – 332K 43R – 332K
WRM0204 ±15ppm – – – 10R – 221K 22R – 221K 43R – 221K
WRM0204 ±10ppm – – – – 22R – 221K 43R – 221K
WRM0204 ±05ppm – – – – 100R – 100K 100R – 100K
WRM0207 ±50ppm R22 – R91 – 1R – 8.2M 10R – 1M – –
WRM0207 ±25ppm – – – 10R – 1M – –
WRM0207 ±15ppm – –––––
WRM0207 ±10ppm – –––––
WRM0207 ±05ppm – –––––
Test Results ∆R/R ±
Stability class
Description 0.25 0.5 1.0
10 Ω– <75 Ω0.22 Ω– <10 Ω
75 Ω– <100 kΩ>100 kΩ– 332 kΩ>332 kΩ– 10 MΩ
Short time overload* ≤0.05% + 0.01 Ω≤0.1% + 0.01 Ω≤0.25% + 0.05 Ω
Bending test* ≤0.05% + 0.01 Ω≤0.1% + 0.01 Ω≤0.25% + 0.05 Ω
Resistance to soldering heat ≤0.05% + 0.01 Ω≤0.1% + 0.01 Ω≤0.25% + 0.05 Ω
Temperature rapid change ≤0.05% + 0.01 Ω≤0.1% + 0.01 Ω≤0.25% + 0.05 Ω
Endurance*
Load life 1000h ≤0.25% + 0.05 Ω≤0.25% + 0.05 Ω≤0.5% + 0.05 Ω
8000 h ≤0.5% + 0.05 Ω≤0.5% + 0.05 Ω≤1.0% + 0.05 Ω
Climatic sequence* ≤0.25% + 0.05 Ω≤0.5% + 0.05 Ω≤1.0% + 0.05 Ω
Damp heat steady state* ≤0.25% + 0.05 Ω≤0.5% + 0.05 Ω≤1.0% + 0.05 Ω
Current noise < 0.05 µV/V < 0.25 µV/V < 3 µV/V
Solderability Dipped area shall be covered with a smooth
and bright solder coating of at least 96%
Voltage coefficient < 0.5 . 106/V
Voltage proof No flashover or breakdown
WRM_C.qxd 28/4/03 10:02 am Page 2
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
The maximum permissible impulse voltage Vmax is the
voltage pulse short overload depending on the impulse time
ti. High ohmic values are protected by the interdependence of
voltage limit and impulse time. This function is given by the
equation.
Vmax = maximum permissible continuous voltage,
ti= pulse time and K = 100 s-1.
2 Maximum Pulse Load
The average load P must not exceed the rated dissipation. For
resistance values above the critical resistance the rated
dissipation is given by the resistance value and the limiting
element voltage Vmax. It is required
Mini Melf
Resistors
WRM Series
© 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
41
Issue C · 04.03
Welwyn Components
Vmax = 2,5 . Vmax + Vmax
1 + ti . K
P = tp . R t1
V2 (t) dt ≤ P
1t2
P
Vmax
That means:
nominal resistance values
time of the pulse period (
t-1
p
= pulse frequency)
pulse voltage
peak voltage of the pulse
rated dissipation of the resistor at ambient
temperature
impulse time ti
3 Continuous and Single Pulse Load
There is a difference between repetitive pulse load
or single pulse load (eg switching events
A higher pulse load Pmax is accepted in the latter case.
4 Pulse Shapes
The diagrams show the maximum pulse load for a rectangular
pulse shape.
Other pulses should be converted into rectangular pulse
shape, having the same energy at given peak voltage.
For exponential pulses the calculation follows:
R
tp
V (t)
V
P
t2 - t1
(P = tp
. P
~ , with = power at the pulse time ti)
ti
P -> 0).
P = tp . R
ti . V2
P = 2 . tp . R
e V2
with e = R . C or e = R
L
t
i
t
i
t
1
t
2
t
V
Rectangular Pulses
e
t
V
Exponential Pulse
0,37 .
V
WRM_C.qxd 28/4/03 10:02 am Page 3
Mini Melf
Resistors
WRM Series
© 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
Welwyn Components
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.
100
10
1
0,1
10 µs 100 µs 1 ms 10 ms 100 ms 1 s 10 s
Pulse Duration ti
Pulse Load Pmax
WRM 0102
WRM 0204
WRM 0207
W
100
10
1
0,1
10 µs 100 µs 1 ms 10 ms 100 ms 1 s 10 s
Pulse Duration ti
Continuous Pulse Load Pmax
WRM 0102
WRM 0204
WRM 0207
W
Single Pulse
Maximum Pulse Load
Continuous Pulses
Maximum Pulse Load
WRM_C.qxd 28/4/03 10:02 am Page 4
