Overheating Protection - Keithley 2651A Reference Manual

Model 2651A High Power System SourceMeter® Instrument Reference Manual

Overheating protection

Proper ventilation is required to keep the High Power System SourceMeter
overheating. Even with proper ventilation, the Model 2651A can overheat if the ambient temperature
is too high or the High Power System SourceMeter
periods of time. The High Power System SourceMeter
protection circuit that will turn the output off if the instrument overheats. When the over-temperature
protection circuit turns the output off, a message indicating this condition is displayed. You will not be
able to turn the output back on until the instrument cools down.
Power equations to avoid overheating
To avoid overheating, do not operate any channel on the instrument in a manner that forces the
instrument to exceed the maximum duty cycle (DC
equation (on page 4-3) below. Factors such as the ambient temperature, quadrant of operation, and
high-power pulse levels (if applicable) affect the maximum duty cycle. Exceeding the calculated
maximum duty cycle may cause the temperature protection mechanism to engage. When this
happens, an error message displays and the instrument output is disabled until the internal
temperature of the instrument is reduced to an acceptable level.
You do not have to be concerned about overheating if all of the following are true:
•
The instrument is used as a power source and not a power sink.
•
The ambient temperature is ≤ 30° C.
•
Extended operating area (EOA) pulsing is not being performed.
However, if any one of these is false, the instrument may overheat if operated in a manner that
exceeds the calculated maximum duty cycle, DC
The maximum duty cycle equation is derived from the power equation below by solving for DC
The general power equation describes how much power an instrument channel can source and sink
before the total power cannot be fully dissipated by the instrument's cooling system. This equation
incorporates all of the factors that can influence the power dissipated by the instrument.
General power equation
|(V
OA
2651A-901-01 Rev. A / March 2011
)(I )| DC
– V + |(V
P P MAX
®
Instrument is operated in sink mode for long
®
Instrument has an over-temperature
), which is computed using the
MAX
.
MAX
)(I )| (1 – DC
– V
OA B B
Section 4: Theory of operation
®
Instrument from
General power
) (P )
– P
MAX CS DER
.
MAX
4-3