DOCUMENT 301900, REVISION D
8 EPISENSOR USER GUIDE
Since the EpiSensor contains no high voltage circuitry and is not connected
to AC power, safety concerns arise from the instrument-end of the
connection cable.
When using your own power system, be sure that AC power is fully isolated
from the DC power supplied to the EpiSensor and that the power supply is
safely grounded.
If the EpiSensor is separated from the recorder or power supply by a long
distance, observe the precautions discussed in the section on long cables.
EMI/RFI
To prevent EMI/RFI susceptibility and interference, an overall shield should
be provided and cables must be carefully constructed to ensure shields
terminate to the connector to provide a full 360$ termination. This provides
a low impedance path for high frequency noise to ground and does not
allow the high frequency to "leak" onto unprotected wiring in the cable.
The case of the instrument and the shields should generally be grounded to
a low impedance earth ground.
The EpiSensor contains transient protection circuitry that will shunt
damaging currents to its case ground connection and prevent damage from
ESD and lightning-induced transients.
Use the stainless steel screw on the flange of the instrument as the case
ground connection point. To be effective, this point must be connected to a
low impedance earth ground.
Providing a low-impedance earth ground can be challenging, because a
safety earth ground for AC wiring is not necessarily a good low impedance
ground! A safety earth ground is designed to provide a path for AC fault
current to flow to ground, trip the fuses in the power system and prevent
electrocution.
Since AC power is only at 50 or 60Hz, the primary factor restricting the
flow of current is the DC resistance of the ground. Lightning, ESD, and
EMI/RFI are high frequency currents. The flow of these currents is
restricted by the impedance of the ground at the frequency of interest, and
rather than being dominated by DC resistance, the inductance of the
connection is the primary component of this impedance.
Thus, we require both a low impedance ground and a low impedance
connection to that ground. To provide low impedance connection to the
ground:
Attach the EpiSensor grounding screw to the ground with a heavy-gauge
wire 3 mm in diameter (<10 AWG) or thicker, or a tinned copper braid at
least 1.2 cm (1/2") in width.
To be effective this wire or braid must be as short as possible and should
have no sharp turns. The connection to the grounding point should have a
large-area connection that is tightened and not subject to corrosion. Special
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