5300 Series TECSource User’s Manual · Page 33
Compensating for Cable Resistance
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 compensation, the Cable R setting in the menu
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 ITE+ and ITE–
connections, making sure whatever you are using to short the terminals is not
itself adding resistance to the circuit. 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 DB15 connector and a soldering
iron to solder the ITE+ and ITE– 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 (or the maximum
current of your controller, if less). 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 stabilize, 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 Cable R menu 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.
Internal Power Management
The TECSource is a powerful instrument, capable of delivering upwards of
180W in some custom configurations. When driving a low voltage load at higher
currents, a condition can arise where the voltage of the load is too low, and
unaddressed, would result in excessive heat inside the instrument.
To manage this internal thermal load, the TECSource relies on two methods of
power control: a tunable power supply and current limiting. Where possible, the
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