Vaisala WXT520 Manuel d'utilisateur télécharger pdf (Page 12)

when it is 50, set Range=4-20mA, Lo=0,

and Hi=50. The 7470 does not know the

measurement unit – it is defined in the

Vaisala configuration.

Finally click the Save to EEPROM button.

Polarization

Every RS-485 bus should have one or two

devices capable to feed a weak current on

the bus. The purpose of the current is to

have a small (0.2 to 5 V) voltage between

the data wires when nobody is

transmitting on the bus. This is called fail-

safe, polarization, or biasing. If there is no

polarization, the devices may receive

phantom data from the bus when it is

idling.

Vaisala WXT520 is not able to provide the

polarization.

The current 7470 model (PCB version 1.2

or newer, since May 2012) is able to

provide the polarization current. Set the

jumper JP4 to position “Polarized” or

“Terminated and polarized” per 7470

manual.

The older 7470's (PCB V1.0-1-1) do not

have a dedicated polarization jumper, but

similar effect can be achieved by selecting

a 2-wire position with jumper JP4.

Testing

Remove the service cable from the

weather station, if still attached, to enable

the auto-transmission. Wire the Vaisala

and 7470 together, if not already.

If using a programming cable, open the

Monitor on MekuWin. Readings should

appear in Ch2 and other items. Analog

outputs should activate.

Several 7470's

Several 7470's can be parallel-connected

in an RS-485 bus and configured to pick

different parts of the Vaisala composite

message.

Troubleshooting

7470 outputs are 0 mA or

0 V

Remove the programming cable, if still attached.

7470 is not receiving proper messages. Make sure that the

weather station is auto-transmitting, and that the baud rates

match. Also check the serial bus wiring.

Vaisala not auto-

transmitting

Remove the service cable, if attached.

Check the configuration once more.

Also look at the troubleshooting instructions in the 7470 manual.

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Vaisala WXT520 Manuel d'utilisateur Page 12

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