Arroyo Instruments TECPak 585 Series, User Manual

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TECPak User’s Manual · Page 27
 Any condition that causes the output to turn off (temperature limits,
sensor limits, etc.)
 Systems with very low P or I terms
In the Auto-Tune fails due to thermal system limitations, you will need to
manually modify the PID parameters as described in the section above or select
factory gain setting.
Turning the output off remotely will cancel the AutoTune process and generate
an E-436 error.
Compensating for Cable Resistance
Because the high currents the
TECPak 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 allows you to specify the cable
resistance, which is then used to dynamically subtract the voltage drop by 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 solding 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 4A. Depending on
your setup, you may first need to change the Mount to User Defined and adjust
the limit to 4A. 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 / 4
The
Cable R value can be changed using Arroyo Control or with the
TEC:CABLER command. Typical values for Cable R are 0.008 to 0.040, but
depend on your actual configuration.