GHM Delta OHM HVAC40 Series, Operating Manual, Page: 10 / 26

HVAC40…
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V1.1
segment and the successive one. Line termination should be applied at both ends of
each segment.
The instrument has a built-in line termination that can be connected or removed
through a short jumper placed at the bottom of the electronic board. If the instrument
is the last or the first device of a network group, connect the termination by placing
the short jumper on the “RT ON” side. If the instrument is not at the end of a network
group, disconnect the termination by placing the short jumper on the side opposite to
“RT ON”.
The cable shield must be connected to both line ends. The cable should have the fol-
lowing features:
•
Characteristic impedance: 120 ohm
•
Capacity: less than 50pF/m
•
Resistance: less than 100 ohm/km
•
Gauge: 0,22 mm 2 (AWG24) at least
The cable maximum length depends on baud rate and cable characteristics. Typically,
the maximum length is 1200 m. The data line must be kept separated from any power
lines in order to prevent interferences on the transmitted signal.
3.2 C
ONFIGURATION DIP SWITCHES IN THE MODELS WITH ANALOG OUTPUT
HVAC4017T…, HVAC40A17T… and HVAC40V17T… transmitters have 4 preconfigured
temperature ranges for the analog output. In order to use a preconfigured tempera-
ture range, it is necessary to set the dip switch 1 to ON and set the temperature
range with the dip switches 2 and 3, according to the following table:
Dip switch
number
Temperature
range
1 2 3
ON OFF ON 0…+50 °C
ON ON OFF -20…+50 °C
ON OFF OFF -20…+80 °C
ON ON ON 0…+80 °C
OFF N.U N.U Set via serial
In the HVAC4017T… and HVAC40V17T… models, with active analog output, a dip
switch is OFF when placed down; instead, it is ON if placed up. The dip switch 1 is on
the left.
In the HVAC40A17T… models, with 2-wire current output, a dip switch is OFF when
placed on the right; instead, it is ON if placed on the left. The dip switch 1 is at the
bottom.
If a temperature range other than the preconfigured ones is desired, it is necessary to
set the dip switch 1 to OFF and set the temperature range via COM AUX serial port.
The dip switch 4 is used to select the relative humidity (R.H.) or the dew point (D.P.)
measurement.