Specifications

PL 3120/PL 3150/PL 3170 Power Line Smart Transceiver Data Book 195
Power Line Test Isolator
The circuit shown in Figure 7.1 is used to create a power mains environment that is isolated from the noise and loading
present on typical power mains. When properly constructed, the circuit provides 60 to 80dB of isolation between the
power mains and the product under test at the communication frequencies of the PL Smart Transceiver. The
effectiveness of the circuit should be verified by using a pair of PLCA-22 analyzers communicating between the power
mains input and the output. To perform this verification, set the PLCA-22 analyzer that is connected to the input side of
the isolator to send packets at 3.5Vpp in UnackPri mode in the C-band. The green bar graph meter on the receiving
analyzer (connected to the “product under test” output) should indicate a signal strength no higher than –60dB (0dB on
the PLCA-22 bar graph meter =3.5Vpp). Without any packet transmission, no LEDs above the –78dB primary and
secondary signal strength LEDs should be illuminated or flashing. Note that Neon power indicators should not be used
on the isolated output, because they frequently produce noise in the –72dB range.
Because the isolator does not completely block communications from other PL 3120, PL 3150, or PL 3170 Smart
Transceivers (or older PLT-2X transceivers) communicating on the power mains, receive testing must only be
performed when there is no other packet activity on the power mains.
Figure 7.1 Power Mains Isolation Circuit
The transformers shown in the circuit are 50/60 Hz, 1:1 isolation transformers. The load (VA) rating of each transformer
should be chosen based on the load requirements of the devices under test. Care should be taken when wiring the
isolator to avoid inadvertent signal coupling between the input and output wiring by spacing the input and output wires
at least 15cm (6 inches) apart.
Test Equipment
In addition to the power mains isolator described in the previous section, the following “off-the-shelf” equipment will be
needed for testing:
• One pair of PLCA-22 Power Line Communications Analyzers (Model 58022). The older PLCA-21 is not
suitable.
• Two PL-20 Line-to-Neutral power line couplers, Echelon model 78200-221.
• Two 50Ω coax cables approximately 30cm long with male BNC connectors on both ends (AMP 1-221128-x or
equivalent).
All capacitors 0.47µF 250VAC (X2 type)
All resistors 20Ω 1 Watt ±5%, unless otherwise indicated
Isolation transformer rating based on load requirements
Line in
Neutral in
Earth
Line out
Neutral out
Earth
From power
mains
To product
under test
R
C
R
R
C
CC
C
C
50 Ω
±5%, 1/4W
C