Tektronix TCPA300 SERIES, Instruction Manual

Page: 53 / 205

Reference Notes
TCPA300/400 Amplifiers and TCP300/400 Series Current Probes Instruction Manual
3- 7
varying duty cycles and levels of continuous current. The ambient temperature in
these two examples is kept constant at 50
°
C.
WARNING.
When using the probe near the upper current limit and maximum
ambient temperature for extended lengths of time, the probe head surface can
become hot to the touch. To prevent injury, keep your hands away from the probe
head until it has had time to cool after disconnecting the probe from the circuit.
To see how noncontinuous current amplitude affects measurement time, look at
the curves for measurements of 200 amps continuous between the two graphs in
Figures 4--8 and 4--9 on page 4--12. Compare the maximum measurement time
allowed for a duty cycle of 20%: At 750 amps, you have 3 minutes of safe
measurement time, versus 17 minutes for a smaller noncontinuous-current
amplitude of 600 amps.
By looking at any of the three graphs, you can also see that when you measure a
noncontinuous current having the same amplitude and duty cycle, the measure-
ment time decreases as the continuous-current amplitude increases.
Finally, compare the two graphs in Figures 4--8 and 4--10 on pages 4--12 and
4--13. Here, the effect of ambient temperature on measurement time is illustrated.
Given a continuous current of 200 A with a noncontinuous current of 750 A, and
having a 20% duty cycle, a 27
°
C increase in temperature yields a 12 minute
decrease in maximum measurement time.
Keep these factors into account when taking measurements to ensure accuracy
and to protect both yourself from injury and the equipment from damage.