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state will shut the output off. The indicator will remain illuminated after a fault until the output is
enabled or power is cycled. In some instances a TEC OPEN fault may occur with high impedance
TECs and can be remedied by reducing the current limit as to reduce the maximum voltage
generated.
SNS OPEN: Indicates that the thermistor or external setpoint resistance has exceeded 50k when
the 100µA or Linearized sensor mode is selected or 500k when the 10µA sensor mode is selected.
Like the TEC OPEN indicator, the output must be on to enable monitoring of SNS OPEN. Detection
of a SNS OPEN state will shut the output off. The indicator will remain illuminated after a fault until the
output is enabled or power is cycled.
I LIMIT: This LED indicates that the current output is limited by the limit setpoint. It is normal for this
indicator to illuminate shortly after turning the output on, or when load power changes significantly. If
the indicator stays on or occasionally turns on after a long period, the controller cannot maintain
temperature due to the power requirements of the load. Changing the temperature setpoint, or
increasing the current limit, if it is safe to do so, can fix this problem.
Output Off/On Button
The OUTPUT off/on switch is located in the lower right-hand corner of the front panel. This
switch has a toggling action which turns the output current of the LDT-5416 off and on. When
the output is active, the LED indicator just above the switch will be lit.
When the OUTPUT is off, it is safe to connect or disconnect sensitive devices from the LDT-
5416, even though the power supply is on. The OUTPUT is off when AC power is first applied to
the instrument. Additionally, there are three other conditions which will automatically cause the
output to reset to the off state:
•
Power Drop-outs - AC line power drop-outs lasting more than about 1 second will trigger an
internal power monitor and cause the output to switch unconditionally to the off state. This
sequence is also initiated when the LDT-5416 is switched off or unplugged.
•
SNS OPEN - If the externally connected thermistor or set point resistor is open, the output is
switched to the off state and the SNS OPEN LED indicator is illuminated.
•
TEC OPEN – If the connected TEC exceeds the rated voltage of the LDT-5416 the output will be
disabled and the TEC OPEN LED will be illuminated.
If any of these conditions occur and the OUTPUT turns off; output may be turned on again by
first correcting the cause of the fault and then pressing the OUTPUT off/on switch.
General Operating Procedures
The discussion below presents guidelines for operation as well as some common operating
procedures.
Warm-Up and Environmental Considerations
To achieve the rated accuracy, allow the LDT-5416 to warm-up for at least one hour before use.
Operate the controller within the environmental limits specified in Chapter 1.
November 2016
9
LDT-5416
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