The KVD-500 Series is a cost-effective, three-terminal, Kelvin Varley Voltage Divider that uses thumbwheel switches.
Circuit Model
The Kelvin Varley Voltage Divider may be thought of as being equivalent to a digital potentiometer, except that it has an additional, variable resistance in series with the wiper arm. See circuit model figure below.
Effect of Series Resistance
The effect of series resistance may be safely ignored in general bridge applications, such as the one shown below. As the bridge comes into balance, the current that flows out of the divider is nominally zero; therefore, the divider effectively "sees" an infinite impedance
Resolution and Precision
The problem with a conventional voltage divider is that it uses a tapped resistor string, which has a fundamental design disadvantage: the resolution of 1 part in 1000 requires 1000 precision resistors.
The Kelvin-Varley Voltage Divider solves this problem by using a clever iterated scheme (see schematic below). In a typical design, each stage provides a decade of resolution and requires only 11 precision resistors. Cascading 3 stages permits any division ratio from 0 to 1 in increments of 0.001 (i.e. resolution of 1 part in 1000).
Features:
• Suitable for use in voltage and current dividers for
calibration and linearity testing
• Eliminates the need for dials & multi-turn potentiometers
• 1 through 6-decade units are available
• Resistor accuracies from 0.01% to 1%
• Available as a stand-alone instrument in a plastic case
or without a case for panel mounting
• Fully customizable for customers' needs
Absolute Linearity:
Linearity deviation, the error between the actual output voltage (VOUT) and the output voltage for a particular setting (S) = [VOUT/VIN] - S Linearity will be smaller than the resistor accuracy.
Power across input terminals:
2 W (others available)
Resistor Accuracy:
Note: Linearity error will be smaller than the resistor error.
X: 0.01% ± 5 mΩ
Q:0.02% ± 5 mΩ
A:0.05% ± 50 mΩ
B:0.1% ± 50 mΩ
C:0.5% ± 50 mΩ
F:1.0% ± 50 mΩ
Operating temperature:
10°C to 50°C
Dimensions:
Without case: 81 mm x 79 mm x 56 mm (3.2" x 3.1" x 2.2")
With case: 120 mm x 79 mm x 56 mm (4.7" x 3.1" x 2.2")
Applications:
See www.ietlabs.com/kelvin-varley-voltage-dividers