Lumel P30U series - 5.9. RS-485 Interface

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5.. RS-45 Interface
 The digital programmable P30U transducers are equipped
withaserialinterfaceintheRS-485standardtocommunicateincom-
putersystemsandwithotherMasterdevices.Asynchronouscharacter
communicationprotocolMODBUShasbeenimplementedontheserial
interface.Thetransmissionprotocoldescribesthemethodsofinforma-
tionexchangebetweendevicesviaaserialinterface.
5..1. Serial interface connection
 RS-485 standard allows direct connection of up to 32
devices on a single serial link with the length of up to 1200 m
(withthebaudrate9600b/s).Inordertoconnectlargernumberofdevices,
it is necessary touse additional intermediate-and-separating systems
suchasPD51madebyLUMELS.A.Connectiondiagramispresented
on the Fig. 3. In order to obtain correct transmission, it is necessary
to connect the lines A and B in parallel to their equivalents in other
devices. Connection should be made with a shielded cable.
Thecableshieldshouldbeconnectedtotheprotectiveterminalasclose
to the transducer as possible (the shield should be connected
totheprotectiveterminalatonepointonly).
 GNDlineisusedforadditionalprotectionoftheinterfaceline
incaseoflongconnections.Insuchacase,GND signalsofalldevices
onRS-485busshouldbeconnected.
 ToobtainaconnectionwithaPC,anRS-485interfacecard
oranappropriateconverter,e.g.PD51orPD10,isrequired.Themethod
ofconnectingdeviceshasbeenshownonfig.29.