CHAPTER 2: INSTALLATION
PQMII POWER QUALITY METER – INSTRUCTION MANUAL 2–17
FIGURE 2–12: Analog Output
As shown in wiring diagrams, these outputs are at Terminals 25 to 28 and share Terminal
24 as their common. Shielded cable should be used, with only one end of the shield
grounded, to minimize noise effects.
Signals and power supply circuitry are internally isolated, allowing connection to devices
(PLCs, computers, etc.) at ground potentials different from the PQMII. Each terminal,
however, is clamped to ±36 V to ground.
2.2.10 Analog Input (Optional)
Terminals 22(–) and 23(+) are provided for a current signal input. This current signal can be
used to monitor any external quantity, such as transformer winding temperature, battery
voltage, station service voltage, transformer tap position, etc. Any transducer output
ranges within the range of 0 to 20 mA can be connected to the analog input terminals of
the PQMII. See 5.3.3: Analog Input for details on programming the analog input.
2.2.11 RS485 Serial Ports
A fully loaded PQMII is equipped with three serial ports. COM1 is a RS485 port available at
the rear terminals of the PQMII which is normally used as the main communications
interface to the system. COM2, which is also a rear RS485 port, can be used for data
collection, printing reports, or problem analysis without disturbing the main
communications interface. COM3 is a front panel RS232 port that can be used for setpoint
programming or recording using the EnerVista PQMII Setup Software.
A serial port provides communication capabilities between the PQMII and a remote
computer, PLC, or distributed control system (DCS). Up to thirty-two PQMIIs can be daisy
chained together with 24 AWG stranded, shielded, twisted-pair wire on a single
communication channel. Suitable wire should have a characteristic impedance of 120 W
(such as Belden #9841). These wires should be routed away from high power AC lines and
other sources of electrical noise. The total length of the communications wiring should not
exceed 4000 feet for reliable operation. Correct polarity is essential for the
communications port to operate. Terminal (485+) of every PQMII in a serial communication
link must be connected together. Similarly, the (485–) terminal of every PQMII must also be
connected together. These polarities are specified for a 0 logic and should match the
polarity of the master device. If the front panel RX1 or RX2 lights are flashing, this indicates
that the PQMII is receiving data. If the front panel TX1 or TX2 lights are flashing, this
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