Tektronix TCPA300 SERIES, Instruction Manual

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TCPA300/400 Amplifiers and TCP300/400 Series Current Probes Instruction Manual
3- 1
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
fields 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 flowing through the conductor will cause a residual offset in the
current probe, and the amplifier may report an inaccurate result.
If the impedance of your circuit is higher than that shown in Table 3--1, the
degauss procedure will succeed because the amplifier will be able to saturate the
probe core. While degauss occurs, the probe will induce a voltage in the
unpowered circuit. This also appears in Table 3--1. 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 3- 1: Unpowered circuit degauss limits
Probe type Minimum circuit resistance Maximum induced voltage
TCP312 10 m
Ω
40 mV at 200 Hz
TCP305 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