Series 2000 Communications Handbook - Soliton

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Digital Communications HardwareSeries 2000 Communications Handbook2.3. CABLE SELECTIONThe cable selected for the digital communications network should have the followingelectrical characteristics:• Less than 100 ohm / km nominal dc resistance. Typically 24 AWG or thicker.• Nominal characteristic impedance at 100 kHz of 100 ohms.• Less than 60 pF / m mutual pair capacitance, (the capacitance between two wires in apair).• Less than 120 pF / m stray capacitance, (the capacitance between one wire and all othersconnected to ground).• For RS422/485 applications, use twisted pair cables.The selection of a cable is a trade off between cost and quality factors such as attenuation andthe effectiveness of screening. For applications in an environment where high levels ofelectrical noise are likely, use a cable with a copper braid shield, (connect the shield to anoise free ground). For applications communicating over longer distances, choose a cablethat also has low attenuation characteristics.In low noise applications and over short distances it may be possible to use the groundedscreen as the common connection. Connect the common to the grounded screen via a 100ohm, 1/4W carbon composition resistor at the PC and all instruments.For RS422/485 it is possible to operate the system with unscreened twisted data pairs, groundis used as the common connection. Connect the common to ground via a 100 ohm, 1/4Wcarbon composition resistor at the PC and all instruments. This system is not recommended.The following list is a selection of cables suitable for RS 422/485 communication systems,listed in order of decreasing quality.Cables marked '*' are suitable for use with the wiring descriptions that follow.Cables marked '**' use a different colour coding from that used in the wiring descriptions.BeldenNoDescription9842 2 twisted pairs with aluminium foil screen plus a 90% coverage copper screen **9843 3 twisted pairs with aluminium foil screen plus a 90% coverage copper screen **9829 2 twisted pairs with aluminium foil screen plus a 90% coverage copper screen9830 3 twisted pairs with aluminium foil screen plus a 90% coverage copper screen *8102 2 twisted pairs with aluminium foil screen plus a 65% coverage copper screen8103 3 twisted pairs with aluminium foil screen plus a 65% coverage copper screen *9729 2 twisted pairs with aluminium foil screen9730 3 twisted pairs with aluminium foil screen *2-4 Series 2000 Communications Handbook Part No HA026230 Issue 2.0 Feb-00
Series 2000 Communications HandbookDigital Communications HardwareThe following are a selection of cables suitable for RS 232 communication systems listed inorder of decreasing quality;Part numberAlpha Belden Description8102 2 twisted pairs with aluminium foil screen plus a 65% coveragecopper screen **5472 9502 2 twisted pairs with aluminium foil screen *2403 8771 3 separate wires with aluminium foil screen **2.4. GROUNDINGEnsure all ground points are noise free.To reduce interference from external electrical signals, ground the cable screen at a singleground point. There must not be multiple ground paths in a single cable run. When using aKD485 Communications Adapter unit, do not connect the screen from one side of theinterface to the other. Rather, ground each of the cables separately at a local ground point.The digital communication outputs of all Series 2000 instruments are isolated. To avoidcommon mode noise problems, connect the common line to ground at one point through a100 ohm, 1/4W, carbon composition resistor. The resistor will limit the ground current.2.5. WIRING GENERALRoute communications cables in separate trunking to power cables. Power cables arethose connecting power to instruments, relay or triac ac supplies and wiring associated withexternal switching devices such as contactors, relays or motor speed drives.Communication cables may be routed with control signal cables if these signal cables are notexposed to an interference source. Control signals are the analogue or logic inputs andanalogue or logic outputs of any control instrument.Do not use redundant wires in the communications cable for other signals.Ensure cable runs have sufficient slack to ensure that movement does not cause abrasion ofthe insulating sheath. Do not over tighten cable clamps to avoid accidental multiplegrounding of the screen conductors.Ensure that the cable is ‘daisy chained’ between instruments, i.e. the cable runs from oneinstrument to the next to the final instrument in the chain.Series 2000 Communications Handbook Part No HA026230 Issue 2.0 Feb-00 2-5
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Series 2000 Communications Handbook - Soliton

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