What Is The Output-Off State? - Keithley 2450 Reference Manual

Model 2450 Interactive SourceMeter® Instrument Reference Manual

What is the output-off state?

When the source of the instrument is turned off, it may not completely isolate the instrument from the
external circuit. You can use the output-off setting to place the Model 2450 in a known, noninteractive
state during idle periods, such as when changing the device under test. The appropriate output-off
state depends on your system and the device under test. Different types of connected devices or
loads require different behaviors from the Model 2450 when the output is turned off. For example, a
passive device such as a diode is not affected by a 0 V source connected across its terminals when
the output is turned off. However, connecting a 0 V source to the terminals of a battery causes the
battery to discharge.
The output-off states that can be selected for a Model 2450 are normal, high-impedance, zero, or
guard.
Carefully consider and configure the appropriate output-off state, source, and source limits before
connecting the Model 2450 to a device that can deliver energy, such as other voltage sources,
batteries, capacitors, or solar cells. Configure recommended instrument settings before making
connections to the device. Failure to consider the output-off state, source, and source limits may
result in damage to the instrument or to the device under test (DUT).
When the Model 2450 is set to the normal output-off state, the following settings are made when the
source is turned off:
• The measurement sense is set to 2-wire
• The voltage source is selected and set to 0 V
• The current limit is set to 10 percent of the full scale of the present current range
• OUTPUT OFF is displayed in the Home page Source area
• The Source button on the Home page shows the output that will be sourced when the output is turned
on again
When the zero output-off state is selected, when you turn off the output:
• The measurement sense is changed to 2-wire sense
• The source function is set to voltage
• The source voltage is set to 0
• Set the range to the presently selected range (turn off autorange)
• Program the voltage DAC to zero, and the current DAC to full scale of the present current range.
• When the zero output-off state is selected, you can use the instrument as an ammeter because it is
outputting 0 V.
When the high-impedance output-off state is selected and the output is turned off:
• The measurement sense is set to 2-wire
• The output relay opens, disconnecting the instrument as a load
Opening the relay disconnects external circuitry from the inputs and outputs of the instrument. To
prevent excessive wear on the output relay, do not use this output-off state for tests that turn the
output off and on frequently.
The high-impedance output-off state should be used when the instrument is connected to a power
source or another source-measure instrument. In some cases, it may also be appropriate for devices
such as capacitors.
2450-901-01 Rev. B/September 2013
Section 9: Frequently asked questions (FAQs)
9-11