
Figure 10 HMP155A/E block diagram and wiring
The left side of the figure shows the HMP155A/E block diagram. The right side shows an
example of connections.
Make sure that the analog ground (A
GND
) and the power ground (GND) are
isolated from each other. If they are not isolated, analog T and RH readings may
be disturbed.
3.3.2 Temporary RS-485 connection option
To have a temporary RS-485 connection in the passive output version, hold down the
ADJ
button when switching on the probe, see
. When HMP155 starts, pins 2
and 6 have the RS-485 signal. See
. After the next startup, the default signals
return to the pins.
The active output version with 2 voltage channels includes also a solid RS-485 connection with
dedicated signal pins that can be used as a temporary digital service port.
Do not use both digital and analog outputs in parallel continuously. It may affect
the temperature measurement accuracy due to increased power consumption
and probe self-heating.
More information
‣
‣
Chapter 3 – Installation
35
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