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I am trying to set up a Vaisaila WMT702 (configured for RS-485) ultrasonic anemometer with a CR3000. I am making use of the SDM-SIO1A in order to make the connection between the logger and instrument. I have followed the guidance in the relevant Vaisala and Campbell manuals, however I am not able to get anything other than garbled text or single question marks (hex 3F) back as a reply from the anemometer. I would be grateful to anyone who has managed to set up a WMT702 using RS-485 for any advice.

You might have a baud rate mismatch. It is easiest to get that sorted out if the sensor is set on an automatic output.

 Here is a program I wrote a while back for a WMT702. Your comport number of course will be different. For using the SDM-SIO1A in RS485 mode, the format parameter in SerialOpen will be different. There is a table in the SDM-SIO1A manual.

'CR1000 Series Datalogger
'WMT702 programed to output at 2Hz automatic on sensor's com2, RS232 19200 baud 8N1, data format 23

'Declare Public Variables

Const SensorPort1 = Com3
Const SensorPort2 = Com4

Public WindSpd_1, WindDir_1,WindSpd_2,WindDir_2
Public WindSensorStat_1 As Long, WindSensorStat_2 As Long
Public PTemp, batt_volt
Dim NBytesReturned
Dim ReturnedData As String * 256
Public SubStrings(9) As String * 32

'Define Data Tables
DataTable (Test,1,1000)
  DataInterval (0,15,Sec,10)
  Minimum (1,batt_volt,FP2,0,False)
  Sample (1,PTemp,FP2)
EndTable


'Main Program
BeginProg
  SerialOpen (SensorPort1,19200,3,0,512)
  SerialOpen (SensorPort2,19200,3,0,512)
  Scan (1,Sec,0,0)
    PanelTemp (PTemp,250)
    Battery (batt_volt)
    'Enter other measurement instructions
    'Call Output Tables

    SerialInRecord (SensorPort1,ReturnedData,&h24,0,&h0d0a,NBytesReturned,01)
    'returneddata = 999.00,999.00,00.00,00.00,331.30,00.3,23.3,20.0,40
    SplitStr (SubStrings(),ReturnedData,",",9,0)
    WindSensorStat_1 = SubStrings(9)
    WindSpd_1 = SubStrings(1)
    WindDir_1 = SubStrings(2)
    SerialInRecord (SensorPort2,ReturnedData,&h24,0,&h0d0a,NBytesReturned,01)
    'returneddata = 999.00,999.00,00.00,00.00,331.30,00.3,23.3,20.0,40
    SplitStr (SubStrings(),ReturnedData,",",9,0)
    WindSensorStat_2 = SubStrings(9)
    WindSpd_2 = SubStrings(1)
    WindDir_2 = SubStrings(2)

    'Example:
    CallTable Test
  NextScan
EndProg