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RS-485 INCOM Sum Because different frequencies are delayed and attenuated by different amounts, a waveform rich in harmonics is distorted after passing.

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Presentation on theme: "RS-485 INCOM Sum Because different frequencies are delayed and attenuated by different amounts, a waveform rich in harmonics is distorted after passing."— Presentation transcript:

1 RS-485 INCOM Sum Because different frequencies are delayed and attenuated by different amounts, a waveform rich in harmonics is distorted after passing through an LC circuit. Harmonic Spectra 1st 3rd 5th InputOutput On the contrary, a pure sinusoid, while delayed and attenuated, keeps its original waveshape after passing through an LC circuit. Physical Signaling Differences

2 Detecting RS-485 1s and 0s Receivers than convert serial bit streams into parallel data are called UARTs (Universal Asynchronous Receiver Transmitters). A UART determines whether the serial stream contains a 1 or a 0 by sampling at the bit rate (9600, 19.2 k, etc.) For better error immunity it typically samples 2 or 3 times per bit. Two bit readings in a row must be the same for the UART to declare a 1 or a 0. With distorted wave shapes, the UART will typically be observing a data stream where the bit value changes from within a bit time. This can cause the UART to declare various errors (such as framing or parity) and discard the byte ?1?

3 INCOM Decoding Since the waveshape is not changed, it is still easy to detect the difference between a 1 and 0 from an Frequency Shift Keyed (FSK) signal. INCOM signals are not as affected by impedance mismatches (taps, Ts, Ys, etc.). Consequently the cabling rules are more relaxed than with RS

4 Excerpt (Page 33) from RS-485 Based Installation Manual

5 Noise Immunity RS-485 INCOM Since RS-485 decides if a signal is a 1 or a 0 by examining the amplitude, external events can mask the true value. INCOM FSK uses a bandpass filter to eliminate signals substantially above or below 100 kHz. Therefore large amplitude interfering signals removed Delay S1 S2 S1 + S2 Delay S1 S2 S1 + S2

6 INCOM Vs RS-485

7 ABCDEFGHIJ ABCDEF THE INFORMATION ON THIS DRAWING IS THE PROPERTY OF EATON CORPORATION. IT IS DISCLOSED IN CONFIDENCE AND IS NOT TO BE REPRODUCED, USED OR DISCLOSED EXCEPT FOR THE PURPOSE FOR WHICH FURNISHED. CUTLER-HAMMER POWER MANAGEMENT PRODUCTS CENTER DWG NO TITLE DFTRDATE APPDDATE APPDDATE ENG. REF.DATE NEXT REF.DATE SHEET NO SIZE A REVISION 1 SCALE NONE DIRECTORY DGL11-DEC-98 1 OF 1 Parking Garage TerminalParking Lot IED IN 1 Shield 3 IP 2 RJ-11 CONIInstall in PC Phoenix Contact RJ-11 to Terminals Cutler-Hammer IMPCABLE or Belden 9463 (or equivalent in Plenum) PONI Typical Switchboard Tap IQ Analyzer PONI IQ Analyzer Typical max RS-485/ 232 Belden 9207 (or equivalent in Plenum) RS-232 IQ Analyzer Typical PONI 131 RS-485 Device Ethernet Hub To PDS Ethernet 10BASE-T RJ-45 IED RS-485 Network This design places brings all network (Lighting Control and Power Monitoring) back to the Central Plant. These taps are legal with INCOM wiring. These are not legal with RS- 485 RS-485 Network INCOM Network

8 RS-485 and INCOM Wiring Rules RS-485 Node IQ Node 200 feet IQ Node IQ Node IQ Node IQ Node Total Cable Length to = 13 x 200 = 2600 feet Conduit space required = sufficient for 2 twisted pairs Total Cable Length to = 9 x 200 = 1800 feet (70% of the RS-485 system) Conduit space required = sufficient for 1 twisted pairs RS-485 Node RS-485 Node RS-485 Node RS-485 Node 200 feet

9 Excerpts (Page 34) from RS-485 Based Installation Manual

10 Reduce Total Cost of Ownership l Reduce initial installed cost l Lower operating cost l Reliability & Safety l Maximize capital utilization l Better customer service


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