Omega Engineering CN8260 Remote Communications Options, Wiring diagram for digital communications

CN8240 & CN8260 Series Communications & Options

Digital

Communications Option

Remote Communications Options

RS-232

This method allows bidirectional data transfer via a three-conductor cable consisting of signal ground, receive input and transmit output. It is recommended for communication distances less than 50 feet between the computer termi- nal and the instrument. Note: Multiple instruments cannot be connected to the same port.

The RS232 port is optically isolated to eliminate ground loop problems. Typically, “Data Out” of the computer/ terminal connects to the “RCV” terminal. “Data In” connects to the “XMT” terminal. If shielded cable is used, it should be connected to the frame ground at one end only. Signal ground is to be connected at appropriate ground terminals (refer to wiring diagram on bottom of this page).

RS-485

The RS485 multipoint capability allows up to 32 controllers to be connected together in a half-duplex network or up to 100 controllers with an appropriate communications repeater.

This method allows bidirectional data transfer over a twisted pair cable. The twisted pair cable is a transmission line; therefore, terminating resistors are required at the most distant ends of the line to minimize reflections (typically 120 ohms at each end). The RS485 circuit is fully optically isolated, eliminating ground loop problems. Parallel drops from the transmission lines should be kept as short as possible; however, the line may be daisy-chained at each controller. The polarity of the line is important and each device will specify an “A” (+) and “B” (-) connection.

Figure 1. Wiring diagram for digital communications.

DIGITAL COMMUNICATIONS

RCV	XMT	SIG GND
B(-)	A(+)	SIG GND

RS 232 RS 485

1		1
		1
2	23	24 12
3		13
4		14
5		15
6		16

Three remote communications options are available for the CN8240/CN8260 which allow interfacing to remote devices utilizing the most common industry standards: RS232 and RS485.

Call factory for a recommended RS485 converter.

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