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Power On / Off
The POWER button applies power to the LDT-5412B.
I LIMIT Knob
The current LIMIT knob allows the user to set the upper limit of the output current. The user may
adjust the output current from zero (LIMIT knob turned fully counterclockwise CCW) to 2 Amps
(LIMIT knob turned fully clockwise CW). This LIMIT knob is recessed to prevent accidental
readjustment of the output current during operation.
The LIMIT current value is not displayed, but the adjustment is linear. For example, setting the
LIMIT knob half-way between 0 and 2 Amps will limit the output current to 1 Amp. A more
accurate LIMIT setting may be attained by the following procedure:
1. Connect a short between pins 2 and 3 of DB15 (TE OUTPUT connector on rear panel). Connect
a 10 k resistor across pins 7 and 8 of DB15.
2. Set the DISPLAY MODE switch to TE CURRENT. Turn the OUTPUT switch on (LED lit). Adjust
the Main Control Knob fully counter-clockwise (CCW).
3. Adjust the LIMIT control until the display reads the desired limit current. Turn the OUTPUT off,
remove the short from pins 2 and 3 of DB15, and remove the resistor form pins 7 and 8 of DB15.
During operation the TE output current is unconditionally limited to the value set by the LIMIT
adjustment
Setpoint Adjustment Knob
resistance (decrease the temperature) and rotating counterclockwise will decrease the resistance
(increase the temperature). When the LDT-5412B is in °C LINEARIZED FOR 10k rotating the
knob counter clockwise will increase the temperature and when rotating clockwise will decrease the
temperature. This is due to the negative temperature coefficient of NTC thermistors where in a
decrease in resistance represents an increase in temperature.
Display Mode and 7 Segment LED Display
Using the button located under the DISPLAY MODE will allow the user to cycle between ACTUAL,
SET, and TEC CURRENT on the 7 segment LED display. When the ACTUAL LED is illuminated the
display reads the measured resistance or temperature (linearized mode) of the thermistor, the SET
LED when illuminated displays the set point resistance or temperature (linearized mode), and when
the TE CURRENT LED is illuminated the LDT-5412B will display the actual measured TEC current.
Error Indicators
TEC OPEN: Indicates that the thermoelectric voltage exceeds the rated compliance voltage of the
instrument. The output must be on to enable monitoring of TEC OPEN. Detection of a TEC OPEN
March 2013
The Setpoint Adjustment knob is located on the upper right side of the LDT-
5412B front panel and is used to set the desired operating, or setpoint,
resistance or temperature of the load. The setpoint may be set from 0.00kΩ
to ~20.00kΩ when the instrument is in the 10µA Sensor Mode (see
SENSOR MODE below), from 0.0kΩ to ~200.0kΩ in the 100µA mode and
from approximately 10°C to 70°C but will only meet the stated accuracy
specification when set between 10°C and 40°C (see LINEARIZED MODE
below). Rotating the knob clockwise in 10/100 µA mode will increase the
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LDT-5412B
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