Tektronix TCP300A, User Manual

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Reference Notes
These notes are provided to help you utilize the full potential of the TCPA300
and TCPA400 current probe systems.
Degaussing a Probe with an Unpowered Conductor in the Jaws
Under almost all conditions, you can degauss your current probe while a conductor
of an unpowered circuit is clamped in the jaws. The advantage of degaussing
with an unpowered circuit is that any offset from stray DC magnetic
fi elds are
compensated. In an automated environment, degaussing with the conductor in the
probe jaws eliminates the need to manually remove the probe.
NOTE.
Be certain that the conductor in the probe jaws is completely unpowered.
Any current fl owing through the conductor will cause a residual offset in the
current probe, and the ampli fi er may report an inaccurate result.
If the impedance of your circuit is higher than that shown, the degauss procedure
succeeds because the ampli
fi er is able to saturate the probe core. (See Figure 12
on page 25.) While degauss occurs, the probe induces a voltage in the unpowered
circuit as shown. (See Figure 12 on page 25.) Your circuit must be able to absorb
this induced voltage. With low impedance circuits, several amperes may be
induced in the circuit being measured. This may be of concern when you are
using very small conductors.
Table 4: Unpowered circuit degauss limits
Probe type
Minimum circuit
resistance
Maximum induced voltage
TCP312A 10 m Ω 40 mV at 200 Hz
TCP305A 5 m Ω 40 mV at 200 Hz
TCP303 5 m Ω 30 mV at 200 Hz
TCP404XL 1 m Ω 15 mV at 100 Hz
TCPA300/400 Ampli fi ers and TCP300A/400 Series Current Probes User Manual 23