C.3 md485 multidrop interface option – Campbell Scientific HMP155A Temperature and Relative Humidity Probe User Manual

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Appendix C. Interfacing with HMP155A RS-485 Output

C.3 MD485 Multidrop Interface Option

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

the HMP155A to the datalogger’s CS I/O port. Connect the MD485’s CS I/O

port to the datalogger’s CS I/O port with an SC12 cable. Sensor wiring to the

MD485 and the datalogger is documented in the example program below.

The HMP155A has a default RS-485 baud rate of 4800, which must be

changed to 9600 to be compatible with the MD485. To change settings in the

HMP155A, Vaisala’s USB to RS-485 cable is required to interface the

HMP155A sensor to a computer. Commands to change settings are sent to the

HMP155A using a terminal emulator such as Windows HyperTerm.

Vaisala’s USB to RS-485 cable includes a CD with drivers that must be

installed on the computer before the cable can be used. Insert the CD into the

computer’s CD drive and follow the prompts.

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