Kelvin Connections; Kelvin Connections - Voltech ATi User Manual

F
IXTURES
5.5 K
ELVIN
'Kelvin' or 4–terminal connections are commonly used in precision
measurement systems to obtain accurate measurements of impedance. Each
of the ATi's 20 measurement nodes (including the BNC connectors) consists of
two terminals (Power and Sense) to allow complete 4-terminal testing.
Why use Kelvin connections?
Consider measuring a perfect 1.000 ohm resistor to check that it is within its
1% tolerance at dc.
In a standard 2 terminal measurement, there are TWO sources of error:
The resistance of the connecting leads.
The resistance of the contact between the connection and the lead of the
resistor.
R , the resistance of the leads, is fixed and can be compensated for. Let's
L
assume it is 2mΩ for good quality leads.
R , the connection or contact resistance is a variable and cannot be
C
compensated for. R
the pressure applied and the contact surface area--all of which can be difficult
to control. Let's assume R
5 mΩ.
P 5-18
AGE
C
ONNECTIONS
will vary with the cleanliness of the leads and connector,
C
varies from a few mΩ to tens of mΩ, but is typically
C
V AT U
OLTECH I SER
M
ANUAL