Campbell HMP 35A Manuel d'instructions télécharger pdf (Page 33)

Appendix C. Interfacing with HMP155A

RS-485 Output

C.1 RS-485 Interface Options

The HMP155A outputs a 0 to 1 Vdc signal for temperature and relative

humidity that can be measured by all models of Campbell Scientific

dataloggers with model HMP155ACBL1 cable. The HMP155A also has

RS-485 outputs for temperature and relative humidity that can be interfaced to

the CR800, CR1000, and CR3000 dataloggers with model HMP155ACBL2

cable and the SDM-SIO1 Serial I/O Module. Vaisala also sells a cable with

RS-485 outputs which is documented in the example programs below.

The MD485 Multidrop Interface can also be used to interface the RS-485

outputs to the CR800, CR1000, and CR3000 dataloggers. This option requires

a USB to RS-485 cable (available from Vaisala) to change the default baud rate

of the RS-485 output from the default of 4800 to a baud rate supported by the

MD485.

C.2 SDM-SIO1 Serial I/O Module Interface Option

The SDM-SIO1 module is used to interface the RS-485 outputs of the

HMP155A to the datalogger. The SDM-SIO1 functions like a built-in serial

port to the datalogger. Data are buffered in the SDM-SIO1 and retrieved by

the datalogger using standard program instructions.

The SDM-SIO1 connects to the datalogger’s 12V, G, and SDM terminals (C1,

C2, C3). Sensor wiring to the SDM-SIO1 and the datalogger is documented in

the example program below.

C.2.1 Program Example for SDM-SIO1 Module

The following program sends the commands ‘SMODE RUN’ and ‘R’ to enable

the RS-485 output. SerialInRecord and Mid instructions parse the serial string

and put the temperature and relative humidity values into public variables.

C-1

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Campbell HMP 35A Manuel d'instructions Page 33