3
Detector placement should be determined following advice of experts
having specialist knowledge of gas dispersion, the plant processing equipment as
well as safety and engineering issues.
The agreement reached on the
locations of sensors should be recorded
. Crowcon would be pleased to assist
in the selection and siting of gas detectors.
3.2 Mounting
The mounting detail of TXgard-Plus is given in Diagram 1. TXgard-Plus should
be installed at the designated location with the detector pointing down. This
ensures that dust or water will not collect on the sinter and stop gas entering
the detector.
3.3 Cabling Requirement
Cabling to TXgard-Plus must be in accordance with the recognised
standards of the appropriate authority in the country concerned and meet the
electrical requirements of the detector. Crowcon recommend the use of steel
wire armoured (SWA) cable and suitable explosion proof glands must be
used. Alternative cabling techniques, such as steel conduit, may be
acceptable provided appropriate standards are met.
TXgard-Plus requires a dc supply of 10-30 V at up to 100 mA.
Ensure the minimum dc supply of 10 V is observed at the detector, taking into
account the voltage drop due to cable resistance.
For example, a nominal dc supply at the control panel of 24 V has a
guaranteed minimum supply of 18V. The maximum voltage drop
allowed is therefore 8V. TXgard-Plus can demand up to 100 mA and so the
maximum loop resistance allowed is 80 Ohms. A 1.0 mm
2
cable will typically
allow cable runs up to 2000 m. Table 4 shows maximum cable distances
given typical cable parameters.
CSA
Resistance (Ohms per km)
Max. distance
mm
2
(awg)
Cable
Loop m
(ft)
1.0 (17)
18.1
36.2
2000 (6560)
1.5 (15)
12.1
24.2
3000 (9840)
Table 4
: Maximum cable distances for typical cables
Acceptable cross sectional area of cable is 0.5 to 1.5 mm
2
. Table 4 provides
guidance only, actual cable parameters for each application should be used to
calculate maximum cable distances.
3.4 Electrical Connections (4-20mA use)
All connections are made via the terminal board mounted in the base of the
junction box (see Diagram 2). The 3 wires from the 96HD are colour coded
and should be terminated in the corresponding colour coded terminal
(terminals 4, 5 & 6). Terminals 1 (0 Vdc), 2 (10-30 Vdc) and 3 (4-20mA signal)
are connected to the control equipment. TXgard-Plus is factory set as a 4-
20 mA source device unless specified otherwise when ordering (see Section
2 to change configuration). Diagram 3 summarises the electrical
connections.
Note: The junction box and cable armour must be earthed at the
detector and control panel to limit the effect of radio frequency
interference and to maintain electrical safety.
All electrical connections to the optional relays are made via the 6-way
terminal block numbered 7 to 12 on the terminal board in the base of the
junction box (see Diagram 2). The relay contacts are rated
1 A @ 30 Vdc.
4. OPERATION
WARNING
Prior to carrying out any work ensure local regulations and site
procedures are followed.
Never attempt to open the detector or junction box when flammable
gas is present.
Ensure that the associated control panel is inhibited so as to prevent
false alarms.
4.1 Commissioning Procedure
a.
Open the junction box of the detector by loosening the tamper proof grub
screw and removing the lid by rotating it anti-clockwise.
b.
Remove the amplifier and check that all electrical connections have been
made and are correct as per Diagram 3.
c.
Replace the amplifier and close the junction box ensuring that all screws
have been re-fitted correctly.
d.
Apply power to the detector. The status LED will show a steady green
indicating normal operation.
e.
Leave the detector to stabilise for 1-2 hours.
Zeroing the detector (ZERO Mode):
f.
Place the end of ‘CRO-Mag’ over the ‘MENU’. Green Status LED will flash.
Decimal point above ‘ZERO’ will illuminate. Display backlight will illuminate.
Decimal point above ‘INHIBIT’ may flash if the option has been internally
selected.
g.
With no target gas present at the detector, place the end of the ‘CRO-
Mag’ key over the ‘UP’ or ‘DOWN’ arrow pads to make the display read
zero.
Note: Oxygen detectors may be zeroed in fresh air
Calibrating the detector (CAL mode):
h.
Place the end of ‘CRO-Mag’ over the MENU pad. The decimal point above
the word CAL will illuminate. Other indications remain unchanged.
i.
Apply calibration gas to the detector at a flow rate of 0.5 litres/min.
CONTROL EQUIPMENT
SAFE AREA
CONTROL EQUIPMENT
SAFE AREA
+V
0 V
SOURCE
10–30 V
10–30 V
4–20 mA
4–20 mA
0 V
0 V
TXGARD-PLUS
TXGARD-PLUS
SINK
+V
0 V
2
3
1
2
3
1
Diagram 3
: Electrical connections to TXgard-Plus
