Det-Tronics THZ HART Combustible Gas Transmitter - Manual (Page 3)

INSTALLATION
DETECTOR LOCATION AND ORIENTATION
The gas sensor used with the THZ transmitter is a dif-
fusion-based gas sensor. Therefore, it must contact
the target gas in order to provide an accurate gas
measurement. Always remember this when selecting
locations for gas sensor installation.
NOTE
The sensor should be pointed down to prevent the
buildup of contaminants on the gas inlet.
WIRING CONNECTIONS
To provide satisfactory operation, the DEC-THZ toxic
gas detector must be installed as a three-wire device,
as shown in Figure 3. This is due to the fact that elec-
trical isolation is required in order to utilize two current
limiting devices in a single device signal input config-
uration. For this reason, a separate DC common con-
nection is required in addition to the signal input con-
nection.
50 OHM RESISTOR INSTALLATION
When the THZ is used with the Det-Tronics two-wire
C706X line of electrochemical sensors, a 50 ohm
resistor must be installed across the transmitter input
to convert the milliampere signal input to a millivolt
input. During the THZ setup routine using the HART
communication protocol, the user simply scales the
device input for 0-1000 millivolt full scale range, which
is proportional to the 4-20 ma signal output.
3 95-8550
3 4
2
1
PS+ PS–
24 VDC +
COM
SIGNAL
50 OHM RESISTOR
A2150
Figure 3—Rear View of Wiring Compartment
2.76
(7.0)
6.06
(15.4)
4.02
(10.2)
4.88
(12.4)
3.54
(9.0)
3.54
(9.0)
CONDUIT ENTRY SIDE VIEW BRACKET MOUNT SIDE VIEW
A2170
Figure 2—Dimensions of THZ Transmitter in Inches (Centimeters)