Metal Foil
Ultra-Precision
Resistors
Wilbrecht Series WA and Series WB
FEATURES
•
Temperature Coefficient
of Resistance (TCR):
± 2.5 ppm/ °C available
•
Selected TCR Tracking:
maximum for 1 year
to 0.5ppm/ °C (matched sets)
•
Shelf Life Stability: ±25ppm
•
Power Rating: 0.3 Watts at 125°C
•
Load Life Stability: ±150ppm
Maximum
∆R
(2000 hours at
rated power)
to ±1.0%
•
Resistance Tolerance: ±0.005%
•
Resistance range: 2.99 Ohms to
200K Ohms
•
Current Noise: 0.010
•
Thermal EMF: 0.1
V
(RMS)/ Volt of Applied Voltage
V/ °C
Maximum; 0.05 V/ °C Typical;
1 V/Watt
@1K Ohms
•
Rise/Decay Time: 1.0 nanosecond
Manufactured in our Huron, SD factory, the WA and WB series
metal foil ultra-precision resistors are designed for the most stringent
temperature and drift stability requirements. Demanding applications
such as oil field data-logging, commercial flight navigation systems,
and automated IC test equipment routinely use our metal foil resistors.
1400 Energy Park Drive, Suite 18 • St. Paul, MN 55108 • Toll Free (888) 323-8751 • (651) 659-0919 • Fax (651) 659-9204 • www.wilbrecht.com
Ultra-Precision Resistors
Composition of Series Number
Example:
Series WA and Series WB
TCR, Resistance Range, Tolerance, Rated Power
TCR
Series -55˚C (ppm/ ˚C) Resistance
to +125˚C Range ( )
C(±5.0) K(±2.5)
WA
WB
C(±5.0)
K(±2.5)
30 - 150K
30 - 100K
±0.005(V) ±0.01(T)
±0.02(Q) ±0.05(A)
±0.1(B) ±0.5(D) ±1(F)
5 - 30
Resistance
Tolerance (%)
±0.1(B) ±0.5(B) ±1(F)
0.3 up to 100K
0.2 over 100K
Rated Power
(W) at 125˚C
WA C 10K000 A
Tolerance
Resistance Value
TCR: C = ± 5.0ppm/°C; K = ± 2.5ppm/°C
Series: WA WB
Resistance value, in ohms, is expressed by a series of 6 characters. 5 of
which represent significant digits while the 6
th
- R or K- is a dual purpose
letter that designates both the value range (R for ohmic; K for kilo-ohm)
and the location of decimal point.
Power Derating Curve
Configuration
FRONT VIEW
L
W
RESISTANCE
VALUE CODE
TCR
TOLERANCE
DATE CODE
ST
SW
LL
REAR VIEW
H
XXXXXX
CB
YYWW
Adjustment of Resistance Value
LS
Lead Material #22 AWG
Round Solder Coated Copper
TRIMMED PATH
Series
Dimensions
L
mm
7.9 ± 0.2
1.0 max
8.3 ± 0.2
0.3 max
25 ± 5
2.8 ± 0.2
3.81 ± 0.25
2.3 ± 0.2
5.08 ± 0.25
Inches
0.311 ± 0.008
.039 max
0.327 ± 0.008
0.012 max
1.0 ± 0.2
0.110 ± 0.008
0.150 ± 0.010
0.091 ± 0.008
0.200 ± 0.010
WA
WB
SW
H
ST
LL
WA
W
LS
WB
W
LS
FOIL
TERMINAL
PAD
Low TCR nichrome foil, bonded to an alumina substrate, is photoetched to
create a resistance pattern. Sections of the resistance pattern can be trimmed
to provide overall resistance tolerances as tight as ±0.005%. The resulting
current path (arrows in diagram) is stable and will not generate electrical noise
over time.
WA
WB
1
2
3
7
10
1
2
3
4
5
TRANSFER MOLDED EPOXY
MOISTURE BARRIER / BUFFER COATING
PROTECTIVE COATING
NiCr FOIL (ETCHED RESISTIVE ELEMENT)
BONDING LAYER
9
4
5
6
8
6
ALUMINA SUBSTRATE
7
EXPOY STRENGTHENED WELD JOINT
8
SECONDARY LEAD
(FOR MECHANICAL STRESS RELIEF)
9
HIGH TEMPERATURE SOLDER
10
THROUGH HOLE LEAD
Rugged Molded Construction Minimizes Lead Stress
The nichrome foil resistance element is protected by a moisture barrier and
sealed in a molded epoxy housing. Internal secondary leads provide the strain
relief necessary to protect the resistor lead terminations from outside shock
and vibration.
TCR Specifications
+0.6ppm/ °C (0°C to +25°C)
Nominal TCR
“C” TCR
-0.6ppm/ °C (+25°C to +60°C)
+2.2ppm/ °C (-55°C to +25°C)
-1.8ppm/ °C (+25°C to +125°C)
Maximum TCR
±2.5ppm/ °C (+0°C to +25°C and +25°C to +60°C)
Spread from
±2.3ppm/ °C (-55°C to +25°C and +25°C to +125°C)
Nominal
-0.3ppm/ °C (0°C to +25°C)
Nominal TCR
“K” TCR
+0.3ppm/ °C (+25°C to + 60°C)
-1.0ppm/ °C (-55°C to +25°C)
±1.0ppm/ °C (+25°C to +125°C)
Maximum TCR
±2.5ppm/ °C (+0ºC to +25°C and +25°C to +60°C)
±2.5ppm/ °C (-55°C to +25°C and +25°C to +125°C)
Stability
Load Life at 2,000 hours
Load Life at 10,000 hours
±0.015% Max.
∆R
@ 0.3W/+125°C
±0.005% Max.
∆R
@ 0.1W/+70°C
±0.05% Max.
∆R
@ 0.3 W/+125°C
±0.01% Max.
∆R
@ 0.05 W/+125°C
Shelf Life Stability
±0.0025% Max.
∆R
after 1 year
±0.005% Max.
∆R
after 3 years
Current Noise
High Frequency Operation
Rise/Decay Time
Inductance (L)
Capacitance (C)
Voltage Coefficient
Thermal EMF
1.0ns at 1K
0.1 H max.; 0.08 H typical
1.0pF max.; 0.5pF typical
< 0.1ppm/V
0.1 V/ °C max.; 0.05 V/°C typical
1 V/Watt (“C” TCR)
0.010 V(RMS)/Volt of applied voltage (-40dB)
© Wilbrecht Electronics, Inc. 2003
