User's Manual
MAINTENANCE AND TROUBLESHOOTING
Calibration Adjustments
24 LDT-5525
CHAPTER 3
ITE Current Calibration
The following procedure is for calibrating the ITE constant current source for both
polarities of current. During this procedure the ITE current is driven to a series of
pre-determined values. When each of these values is reached and is stable, the
user enters the actual value of the current, as measured by an external DMM. The
LDT-5525 Temperature Controller then automatically calibrates the TEC current
source and limits.
Calibration may be aborted by pressing the OUTPUT switch.
a Set the sensor select (back panel) switch to "100 uA." Set C1 to 0.99, C2 to 2.57.
Connect an (approximately) 15 kΩ resistor to the sensor pins (7 and 8). Connect a
1Ω, 20 W, resistor across the TEC output terminals (pins 1 and 3) and use a
calibrated DMM to measure the voltage across the resistor. Calculate the current in
the following steps by using Ohm's Law:
I = E / R
-where E is the accurately measured voltage across the resistor, and R is the
accurately measured load resistance. A 4-point probe resistance measurement is
recommended.
b Press and breifly hold in both the MODE and DISPLAY switches. This will put the
LDT-5525 into ITE calibration mode. Wait for three seconds for the output to settle to
about 3 Amps.
c Press and hold in the ENBL switch and turn the ADJUST knob until the display
shows the correct value (absolute value of the ITE measurement), as calculated from
Step a.
d Release the ENBL switch. Wait three seconds to allow the ITE current to settle at the
new set point.
e Repeat Steps c and d four more times, once for each of the (automatically set) set
points -3 Amps, +3 Amps, +1 Amp, and -1 Amp. After the value for the -1 Amp (last)
set point is entered, the LDT-5525 Temperature Controller will automatically calibrate
its ITE current limits.
After about 10 seconds, the LDT-5525 Temperature Controller will store the new
calibration data in non-volatile memory.
f After calibration, the I LIMIT will be automatically set to 0.00 Amps. Reset the I LIMIT
to the desired value.