Teledyne T3MIL50 User Manual page 31

Note
Zero
A note about Thermoelectric EMF
When making low resistance measurements, thermoelectric electromotive
force (Vemf) can affect measurement accuracy. Vemf is created at the junction
of two dissimilar metals, such as the contact point of a test lead and the pin
of a DUT. Vemf adds a small but measurable voltage to the measurement.
There are primarily two different methods to compensate for Vemf in low
resistance measurements: Offset Compensation and Vemf Cancelling. The
T3MIL50X uses Vemf Cancelling with the pulse drive signal setting (see page
32).
The Pulse drive mode supplies a positive and a negative measurement current
source.
R
I V
Vemf
This produces a positive and negative measurement voltage across the DUT,
which also includes the Vemf (V1+Vemf & V2+Vemf).
V1
0V
V2
To cancel the Vemf, V2 is deducted from V1 and divided by 2 to get the
average measurement, as shown in the formula below:

( V 1 Vemf )

Vx
Standby mode only applies to hardware with the latest
PCB board. Refer to page 63 for details.
V
0V
Vemf
t
 
( V 2 Vemf )
Where Vx = measured voltage sans Vemf.
2
In this mode, T3MIL50X
outputs no measuring signal on
the Source loop; therefore, the
t
Sense loop can be used as a
voltage meter which can
measure up to +/-10mV for
thermoelectric EMF
measurement. This function is
useful for measuring the Vemf
of thermocouple wires.
MEASUREMENT
31