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SOLUTIONS FOR PRIMARY & SECONDARY LABORATORIES
AC/DC Standard Resistors
20°C
Models SRA & SRB
Eventually all resistance thermometry refers back to one
or more fixed resistors. These are a key element in any
laboratory which measures temperature. The resistors
need to be very stable with time, temperature and
transportation, and they need to have negligible
inductance and capacitance.
They also need to have a long and successful history of
use. Wilkins and Swan at our National Physical
Laboratory (NPL) developed a resistor design flexible
enough to allow windings with various resistance values
to be made available and stable enough to be accepted
world-wide as resistance standards. Particularly
important is that the AC/DC characteristics are the same
up to about 1000 Hz.
Isotech are pleased to be able to offer this design of
resistor and we can calibrate the SRA values in our
laboratory to the following uncertainties.
Value Ω Uncertainty, k=2
1 < 0.09 ppm
10, 25, 100 < 0.08 ppm
400 < 0.15 ppm
Other details including calibration at NPL, UK on
request.
TYPE SRA Values 1, 10, 25 and 100 Ohms
400 Ohms to special order
TYPE SRB Values 1000, 10,000 Ohms
Accuracy of adjustment ±20ppm
Stability 2ppm/year
(0.5ppm/year to special order)
Temperature coefficient 2ppm/°C
of resistance 0.5ppm to special order
Recommended 10 mW
dissipation
Maximum dissipation 1 Watt
Approximate load 6ppm/Watt
coefficient
A.C./D.C. transfer 1ppm 10Ω - 10kΩ
error at 1kHz 5ppm 1Ω
Construction
Element Strain free, immersed in dry
oil (No. 4 Kerosene)
Top panel Bakelite with PTFE inserts
and engraved lettering
Terminal - Current 0BA copper
Terminal - Potential 4BA copper
Earth 6BA brass
Dimensions Container 114 x 76mm dia.
Overall 140 x 83mm dia.
Weight 680g
How to order
Standard Resistor
Please specify type, resistance value and calibration
option.
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