ITE Current Calibration

C H A P T E R 3

MAINTENANC E AND TR OUBLESHOOTING

Calibration Adjustments

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.

aSet 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.

bPress 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.

cPress 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.

dRelease the ENBL switch. Wait three seconds to allow the ITE current to settle at the new set point.

eRepeat 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.

fAfter calibration, the I LIMIT will be automatically set to 0.00 Amps. Reset the I LIMIT to the desired value.

24 LDT-5525