Contemporary Control Systems BASgatewayLX - Manual (Page 6)

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6
power
The BASgatewayLX requires 24 VAC or 24 VDC and draws a commensurate amount of
current. The recommended conductor size is 16–18 AWG. COM is directly connected
to zero volts and the chassis is DC isolated from zero volts. Input connections are
reverse-polarity protected.
wArnInG: Powering devices can present hazards. Read the following carefully.
Since the product incorporates a half-wave rectifier circuit, it can share the same 24
VAC power with other half-wave rectified devices. It can also be powered from a
24 VDC source. A redundant power connection exists for back-up power schemes.
The product incorporates a 3-wire optically-isolated EIA-485 interface for the serial
connection, allowing better circuit protection and noise immunity. To connect to other
3-wire devices simply make a one-to-one connection to the other devices. But when
connecting to 2-wire non-isolated devices, the signal common (SC) on the product
must share the reference used by the 2-wire devices. This is accomplished by tying the
SC pin to COM on the product and by grounding the low-side of each power supply
on all connected devices. In this way all EIA-485 transceivers share the same earth
reference. Notice that the SC pin is signal common and not a shield pin. For shield
connections, use the SH pin. Far-end external termination is required as shown. Near-
end bias and termination are internally supplied within the product.
Figure 6 — Power Options