5400 Series TECSource User’s Manual · Page 43
Correcting the TEC Voltage Measurement
Because the high currents the TECSource can drive through the Peltier, the
voltage loss through the cable and connectors of the system can significantly
affect the TEC voltage measurement. In most cases, accurate voltage
measurements are not needed, and the default compensation of the instrument
is sufficient. To improve the accuracy of voltage measurements, the TECSource
provides two methods to compensate for voltage loss: a software compensation
that requires no additional wiring, or a 4-wire measurement (sometimes called a
“Kelvin” measurement), where the voltage of the TEC is measured with an
independent set of wires.
Software Compensation
For software compensation, the Advanced Menu » Cable R setting allows you
to specify the cable resistance, which is then used to dynamically subtract the
voltage drop by simply using the formula V = IR to calculate the voltage loss,
where I is the TEC ITE current, and R is the Cable R setting. This value is then
removed from the voltage measurement to display an accurate TEC voltage
measurement.
The safest method of calculating cable resistance is to short the TE+ and TE–
connections, making sure whatever you are using to short the terminals is not
itself adding resistance to the circuit, and is rated for the current you intend to
use as the test current. Use short, heavy gauge wires, preferably soldered onto
the terminals to minimize any resistance the short might add. Place the short as
close to the Peltier as is reasonable. A simple approach is to unplug the cable
from the mount and place a shorting plug on the mount end of the cable, which
is easily made from a male connector and a soldering iron to solder the TE+
and TE– pins together. Make sure the Peltier is disconnected to protect it from
current overloading during the test.
Change the instrument to ITE mode and set the current to 5A. Depending on
your setup, you may first need to change the Mount to User Defined and adjust
the limit higher. Turn on the output and after the voltage has stabilized, make a
note of it and turn the output off. Enter the measured voltage into the following
equation to calculate Cable R:
Cable R = Voltage / Current
Enter the resulting values into the Advanced Menu » Cable R entry and return
the instrument to its original configuration. Typical values for Cable R are 0.008
to 0.040, but depend on your actual configuration. Once entered, the displayed
TEC voltages will be adjusted based on the above formula.
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