Campbell Scientific HMP155A HMP155A Temperature and Relative Humidity Probe - Page 37

Appendix C. Interfacing with HMP155A RS-485 Output, C.1 RS-485 Interface Options

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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 RS485 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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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