Campbell Scientific HMP155A Temperature and Relative Humidity Probe - Manual (Page 37)

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