Vaisala HMP155 User Manual download pdf (Page 25)

Chapter 4 ________________________________________________________________ Operation

VAISALA _______________________________________________________________________ 23

CHAPTER 4

OPERATION

This chapter contains information that is needed to operate this product.

Getting Started

After the Vaisala HUMICAP

Humidity and Temperature Probe

HMP155 has been connected to a power supply, the serial line and the

analog outputs are operational depending on product model.

RS-485 Interface

HMP155 supports a two-wire RS-485 communication. The RS-485

interface is non-isolated and offers a maximum communications rate of

19200 bits/s. There is no internal termination for the RS-485 on the

HMP155. If any termination is needed, the bus should be terminated at

both ends. The recommended termination is R termination with 120 Ohm

resistors.

Typically the termination resistors are only needed when the fastest

communications rate (19200 bit/s) is used for longer distances. If the

resistors are used, the possible increase in current consumption should be

taken into account.

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Vaisala HMP155 User Manual Page 25