Vaisala HMP155 - Manual (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.