Crowcon TXgard-IS Plus Installation, Operating And Maintenance Instructions

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TXgard

MANUAL

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JUNHO 2013

TXgard-IS+

Intrinsically Safe

Toxic and Oxygen Gas Detectors

Loop Powered Electrochemical and Galvanic Sensor Types Only

Installation, operating and

maintenance instructions, M07214

Issue 7 January 2010

Contents

1 Introduction .................................................................................. 5

Product overview ........................................................................................ 5

Product description ..................................................................................... 5

2 Installation ................................................................................... 8

General ....................................................................................................... 8

Mounting ..................................................................................................... 9

Cabling requirement ................................................................................... 9

Electrical connections ............................................................................... 10

3 Operation ................................................................................... 13

The operator display panel and keypad ................................................... 13

Using the TXgard-IS+ menus ................................................................... 14

4 Commissioning .......................................................................... 16

Commissioning procedure:

Toxic gas detectors .................................................................................. 16

Commissioning procedure:

Oxygen detector ....................................................................................... 21

5 Maintenance .............................................................................. 24

Routine maintenance ................................................................................ 24

Sensor replacement and servicing of detectors ....................................... 24

6 Fault finding ............................................................................... 26

Appendices

Appendix A

Wiring the TXgard-IS+ to Crowcon control equipment ............ 31

Appendix B

TXgard-IS+ specification.......................................................... 35

Appendix C

Spare parts .............................................................................. 37

Appendix D

Menu system............................................................................ 38

Appendix E

4-20 mA Loops......................................................................... 46

Appendix F

Cabling requirement................................................................. 48

Appendix G

Sensor limitations..................................................................... 51

Warranty Statement ................................................................. 51

Introduction TXgard-IS+

Issue 7 5

1 INTRODUCTION

1.1 Product overview

TXgard-IS+ is an Intrinsically Safe detector for toxic gases or oxygen. It is
suitable for use in Zone 0, 1 or 2, or Division 1/Division 2 hazardous areas
when used with a suitable Zener barrier or galvanic isolator.

TXgard-IS+ is designed to detect a wide range of gases when fitted with
the appropriate electrochemical sensor. Gases include oxygen, carbon
monoxide and hydrogen sulphide. For a full list of supported sensors,
please contact Crowcon.

TXgard-IS+ is a loop-powered instrument providing a 4-20 mA signal
suitable for direct connection to a control panel. Unlike most other 4-20 mA
gas detectors featuring operator display panel (LCD) and keypads, it
combines its power and signal in just two wires, so only one barrier is
required. The instruments are supplied with the mA pre-calibrated, so the
mA does not need re-calibration in the field. The keypad and operator
display panel allow access to many powerful features to help installation
and maintenance, such as:

• true one man calibration

• signal current can be ramped to a desired value to help set-up

control panels

• configurable fault and inhibit currents

• configurable display options

• displaying line voltage - no need to access test points inside

unit

1.2 Product description

TXgard-IS+ comprises of two main parts. The junction box contains the
circuitry, including the PCBs, an operator display panel and keypad. The
sensor is contained in the sensor housing. “Figure 1.1” on page 6.

The sensor comes in a re-usable bayonet sensor housing which is
standard for all gas sensors.

The sensor housing screws into an M20 entry on the junction box.

All electrical connections to the detector are made through the terminal
blocks on the baseboard J2 and J4 (see and in “Figure 1.1” on
page 5). The junction box of TXgard-IS+ has one top-entry M20 cable

TXgard-IS+ Introduction

6 Issue 7

entry for customer use as standard. Side entry versions and gland
adapters are available (contact Crowcon for details).

The Personality Module , mounted on the baseboard, comes in two
varieties: Toxic and Oxygen. It converts the sensor output into a standard
signal which can be interpreted by the processor. The Personality Module
contains a memory chip with calibration data for the associated sensor.
When replacing a sensor, it is not necessary to change the Personality
Module; you simply rezero (Note: not necessary for O2 sensor) and
recalibrate, and the Personality Module stores the new calibration
constants.

When the detector is powered through a suitable Zener barrier or galvanic
isolator, the system is certified Ex ia IIC T4.

Figure 1.1: TXgard-IS+ fitted with toxic sensor

Important

TXgard-IS+ is designed for use in Zone 0, 1 or 2, or Division 1/Division 2
hazardous areas and is certified Ex ia IIC T4 when used with a suitable
Zener barrier or galvanic isolator. Installation must be in accordance with
the recognised standards of the appropriate authority in the country
concerned. TXgard-IS+ should be inspected regularly if used in a dusty
environment. For further information, please contact Crowcon.

Before carrying out any installation work, ensure that local
regulations and site procedures are followed.

J4

TP1

+

TP2

–

J2















CONNECTION TO
CONTROL PANEL

40-200mV
TEST POINTS

RED

BLU

GRN

M20 CABLE ENTRY

BASE BOARD

PERSONALITY
MODULE

SENSOR
HOUSING

Some baseboards may have
J4 in this orientation

Introduction TXgard-IS+

Issue 7 7

Storage Instructions

The sensor used in this detector has a maximum non-powered storage life
of 3 months. Sensors stored within a detector for longer than 3 months
prior to commissioning may not last for the full expected operational life.
The warranty period for the sensor begins from the date of shipment from
Crowcon.

Detectors should be stored in a cool and dry environment where
temperatures remain within the 0-20°C range

TXgardIS+ ATEX, UL and IECEx Intrinsically safe

GAS DETECTOR

TXgard-IS+

TXgard-IS+ Installation

8 Issue 7

2 INSTALLATION

2.1 General

The detector should be mounted where the gas is most likely to be present.
The following points should be noted when locating gas detectors:

• To detect gases that are lighter than air, detectors should be
mounted at high level. Crowcon recommends the use of a
Collector Cone (part no. C01051).

• To detect gases that are heavier than air, detectors should be
mounted at low level.

• To detect gases with similar weight to air, for example,
hydrogen sulphide, mount the detector at normal breathing
height.

• When locating detectors, consider the possible damage
caused by natural events such as rain or flooding. For
detectors mounted outdoors, Crowcon recommends the use of
a spray deflector (part no. C01338).

• Mounting of oxygen detectors requires knowledge of the gas
displacing the oxygen. For example, carbon dioxide is heavier
than air and displaces oxygen at low level. Under these
circumstances oxygen detectors should be placed at low level.

• Consider ease of access for functional testing and servicing.

• Consider how the escaping gas may behave due to natural or

forced air currents. Mount detectors in ventilation ducts if
appropriate.

• Consider the process conditions. Gases that are normally
heavier than air, but are released from a process line that is at
a high temperature and/or under pressure, may rise rather than
fall. Ammonia released from a cooling system may fall rather
than rise.

The placement of the sensors should be decided following the advice of
experts with specialist knowledge of gas dispersion, experts with
knowledge of the process plant system and equipment involved, and
safety and engineering personnel. The agreement reached on the
locations of sensors should be recorded. Crowcon is pleased to assist
in the selection and siting of gas detectors.

Installation TXgard-IS+

Issue 7 9

2.2 Mounting

TXgard-IS+ should be installed at the location with the detector pointing
down. This ensures that dust or water will not collect on the sensor and
stop gas entering the detector.

Figure 2.1: TXgard-IS+ dimmensions

2.3 Cabling requirement

Cabling to TXgard-IS+ must be in accordance with the recognised
standards of the appropriate authority in the country concerned, and must
also meet the electrical requirements of the detector. Crowcon
recommends the use of 2-core twisted pair cable, but there is no particular
restriction as long as it can supply 8 V at 20 mA to the instrument terminals.
Suitable weatherproof glands must be used. Cable should be identified as
being intrinsically safe by some means, for example, by having a blue outer
sheath. Alternative cabling techniques, such as steel conduit, may be
acceptable provided that appropriate standards are met.

TXgard-IS+ requires a dc supply of 8-32 V and is loop powered.
(If mounting in a hazardous area, do not use a higher voltage than the
Zener barrier’s rating, usually 28 V). Ensure there is a minimum supply of
8 V at the detector, taking into account the voltage drop due to cable
resistance and the sense resistance of the control panel to which it is
connected. "Table 2.1" on page 10, shows maximum cable distances
given typical cable parameters (See appendix F for more information).

TXgard-IS+ Installation

10 Issue 7

Table 2.1: Maximum cable distances for typical cables

The acceptable cross-sectional area of cable used is 1.0 to 2.5 mm2.

The table is provided for guidance only. Actual cable parameters for
each application should be used to calculate maximum cable
distance. Assume each termination is 0.5 Ω.

2.4 Electrical connections

All connections to the 4-20 mA loop, and sensor, are made via the screw
terminal connectors mounted on the baseboard in the junction box. “Figure

1.1” on page 6. For further information on how 4-20 mA current loops work,
see "Appendix E". For a worked example of how to calculate if the cable is
suitable, please see “Appendix F”.

“Figure 2.2” below, shows the baseboard in detail. The terminals marked
J4 should be connected to the control equipment using the appropriate +
and – terminals. For further details of wiring the TXgard-IS+ to Crowcon
equipment see "Appendix A".

Figure 2.2: Baseboard

Cross-sectional

area (mm

2

)

Typical resistance

(Ω per km)

Maximum

distance (km)

Cable Loop

1.0 18.1 36.2 2.2

1.5 12.1 24.2 3.3

2.5 7.4 14.8 5.4

Some baseboards
may have J4 in
this orientation

Installation TXgard-IS+

Issue 7 11

TXgard-IS+ is a 4-20 mA sink, loop-powered device designed to work in
safe and hazardous zones 0, 1 and 2 areas when used in conjunction with
an appropriate barrier. Figures 2.3, 2.4 and 2.5 summarise the electrical
connections.

SAFE AREA

Figure 2.3: Electrical connections for safe area

HAZARDOUS AREA

Note: An IS earth connection must be supplied in the safe area, so
as to avoid earth loops and to maintain IS certification.

Figure 2.4: Electrical connections using Zener barrier

TXgard-IS+ Installation

12 Issue 7

Figure 2.5: Electrical connections using galvanic isolator

Operation TXgard-IS+

Issue 7 13

3 OPERATION

3.1 The operator display panel and keypad

The TXgard-IS+ provides an operator display panel through a Liquid
Crystal Display (See “Figure 3.1”). The operator display panel allows you
to communicate with the TXgard-IS+ instrument through a series of text
based menus. Use the operator panel to calibrate the sensor, adjust signal
levels and resolve instrument errors. You may also display information on
serial number, software version and adjusting advanced settings.

The operator display panel provides continual instrument status on the gas
being sensed, the gas reading and the loop current value. A flashing ‘OK’
indicates the system is operational (see "Figure 3.2"). Press the down 
button to display the voltage and temperature (“Figure 3.3” on page 14),
this display will automatically return to the main display after a few
moments.

Figure 3.1: Operator display panel and keypad

Figure 3.2: LCD ‘operator display panel’

TXgard-IS+

5 ppm

4.3mA

CO

OK

LCD
Liquid crystal display

DOWN key

ENTER key

UP key

TXgard-IS+

5 ppm

4.3mA

CO

OK

Gas being detected
eg. CO, H2S, O2

Flashing OK
indicates system is working

UNITS

%orppm

Loop current

TXgard-IS+ Operation

14 Issue 7

Figure 3.3: Power and temperature display (after pressing DOWN key)

3.2 Using the TXgard-IS+ menus

Three buttons are provided to select the menu options and respond to
instrument messages, the  (UP) and  (DOWN) button moves your
selection through the menu list, a cursor ‘ >’ indicates current selection. To
enter that selection, press the  (ENTER) key.

To enter the menu system:

1 Press the  button and then the default password, which

is the down button five times.

2 Press the  button again to exit the menu system if you

decide not to change the instruments settings.

The operator display panel shows the available menus. The TXgard-IS+
has seven standard menus that allow you to calibrate and configure the
instrument. The menu structure for a TXgard-IS+ Toxic detector is shown
in “Figure 3.4” on page 14, detailed menus can be found in Appendix D.

NOTE: the menu for the oxygen detector only varies for the ‘Zero/cal gas’
menu item which is replaced by ‘Cal O2 @ 20.9%’.

To exit the main menu display

1 To exit any menu, use the  key to move the cursor to the

top of the menu list where you will find To gas display.

If you are in a submenu you will need to repeat this and
move the cursor to the top of the menu list to return to the
gas display. Note: UP = OUT.

Tip

To go directly to the bottom of a menu, press  and  simultaneously.
To go directly to the top of a menu, press  and  simultaneously.

The menu will also return to the gas display after a timeout (default 5 minutes).

TXgard-IS+

Power: 21.5V
Temp: 25.0 C

Power V

Temperature

TXgard-IS+ Operation

15 Issue 7

Figure 3.4 Menu structure for TXgard-IS+ toxic detector

See Appendix D and Section 4.2 for further information.

MAIN MENU

To gas display

Inhibit mode

Ramp mA output

Configuration

S/W version

Serial number

Calibrate mA

Clear faults

Zero/cal gas

(cal O2 @ 20.9% gas)

Inhibit mode

Forces instrument

to output Inhibit

current

Clear faults

Clears faults

from display

and unit

Calibration of

zero gas

and sensed

gas

Zero / Cal gas

To main menu

Zero gas

Calibrate gas

Submenu

Calibration of

20.9% gas

Cal O2 @ 20.9% gas

To main menu

Confirm O2 cal

Submenu

Calibration of

4-20mA loop

current

To main menu

Calibrate 4mA

Calibrate 20mA

Calibrate mA

Submenu

Ramp mA output

Manual ramp

of mA output

Configuration

To main menu

Limit 4-20mA

Set inhibit mA

Zero suppress

Damping

Menu timeout

Fatal mA

Non-fatal mA

Display option

Pwr-on inhibit

Help screen

LCD Contrast

Submenu

Display shows

two lines of the

menu list at a

time, use DOWN

key to display

other menu items

Serial number

Displays

serial number

S/W version

Displays

software version

Toxic detectors

Oxygen detectors

To enter Main Menu press ENTER

key then DOWN key 5 times

NORMAL DISPLAY

To gas display

Inhibit mode

TXgard-IS+

0 ppm

4.0mA

CO

OK

-

TXgard-IS+ Commissioning

16 Issue 7

4 COMMISSIONING

The commissioning procedures for toxic detectors can be found in section

4.1. To commission oxygen detectors go to section 4.2.

Warning

Before carrying out any work, ensure that local regulations and site
procedures are followed. Ensure that the associated control panel is
inhibited to prevent false alarms.

4.1 Commissioning procedure:

Toxic gas detectors

NOTE: To prevent false alarms during calibration, enable inhibit mode

prior to zeroing or applying gas (see Figure 3.4). The detector output will
then remain at the preset inhibit level (see Appendix D) for five minutes or
until inhibit mode is cleared manually. “Inhibit” will appear on the normal
operating display when inhibit is active, and the detector will automatically
resume gas level output after five minutes.

Step 1:

Connecting the detector to the control panel
1 Apply power to the detector via 2-way connector J4.

“Figure 1.1” on page 6.

The instrument requires a minimum of 8 V dc at connector
J4 at 20 mA.

2 Leave the detector to stabilise for at least 2 hours.

NOTE: the detector is factory pre-set to automatically

inhibit its mA output for 30 seconds after power-up to
prevent false alarms while the sensor is settling.

Step 2:

Checking the 4-20 mA loop current
This step can be omitted as the TXgard-IS+ is delivered

pre-calibrated, however, if you wish to check the 4-20 mA loop

Tip

As long as the instrument is running, you can see the supply

voltage on the display panel, by pushing the

 button.

Commissioning TXgard-IS+

Issue 7 17

current, then it can be checked as outlined below. Alternatively
the TXgard-IS+ provides a facility to force a known current
through the loop. Refer to the Ramp mA menu item in
Appendix D for instructions.

NOTE: there is no need to disconnect a sensor when calibrating
mA! The mA control circuit is completely independent from the
gas measuring circuit!

1 Connect a digital voltmeter (DVM) across test points TP1

and TP2 on the baseboard (“Figure 1.1” on page 6 or
“Figure 2.2” on page 9). The loop current flows through a
sense resistor between these test points, so a 4 mA loop
current will show as 40 mV on the DVM, and 20 mA will
show as 200 mV.

Step 3:

Zeroing the detector in clean air

Before commencing zeroing the detector, ensure the
instrument is in clean air.

NOTE: Oxygen sensors do not need manual zeroing with the
TXgard-IS+. See section 4.2 for calibration instructions.

1 Enter the menu system by pressing the  button.

2 At the password prompt enter the password, by default this

is the down button  5 times.

3 You should now be in the main menu

. Refer to menu

structure, (“Figure 3.4” on page 15).

4 Move the cursor down and select the Zero/Cal gas

menu item. The submenu list for zeroing and calibrating the
gas appears.

5 Select the Zero gas menu item. The instrument will

display a scrolling text message: ‘Ensure the

instrument is in clean air and the sensor
has settled’.

TXgard-IS+

To gas display
Inhibit mode

>

TXgard-IS+ Commissioning

18 Issue 7

6 Press the  button to start zeroing the detector.

The instrument will display the following message:

When complete the instrument will report a scrolling text
message ‘Zero operation successful’.

7 Press the  button to continue, the display will return to

the Zero/cal submenu.

8 You may now proceed to calibrate the gas on the detector.

Step 4:

Calibrate gas on the detector

Before commencing calibrating gas on the detector ensure you
have sample gas. For Oxygen sensors go to section 4.2.

NOTE: Whilst in calibrate mode, the instrument outputs the
Inhibit current.

If you have just completed step 3 (Zeroing) you will still be in
the Zero/Cal Gas submenu, and can skip to 5.

1 Enter the menu system by pressing the  button.

2 At the password prompt enter the password, by default this

is the down button  5 times.

TXgard-IS+

Zeroing Sensor..

TXgard-IS+

To main menu
Zero gas

>

Commissioning TXgard-IS+

Issue 7 19

3 You should now be in the main menu

4 Select the Zero/Cal gas menu. The submenu list for

zeroing and calibrating the gas appears.

5 Move the cursor down and select the Calibrate gas

menu item

The panel will display a scrolling text message: ‘Apply
calibration gas to instrument ––’.

6 Apply calibration gas (typically half or full scale) to the

detector at a flow rate of 0.5 litre/minute. (Crowcon Flow
Adaptor part No. C03005)

7 Select the  button.

Allow gas reading to stabilise.

Tip

Sticky gases which are rapidly absorbed by connecting pipes
(chlorine, nitrogen dioxide and ozone) are applied at 1 litre /
minute.

TXgard-IS+

To gas display
Inhibit mode

>

TXgard-IS+

150 PPM

13.6mA

CO

OK

GAS

0.5 Litre/min

To clean air
or exhaust
pipe

Crowcon
Flow Adaptor

TXgard-IS+ Commissioning

20 Issue 7

Use  and  buttons to adjust gas reading to calibration
gas value.

Gas value is usually measured in ppm or as %vol (ppb and
%LEL are also available, as appropriate).

8 Select the  button to set the calibration value.

The instrument will display the following message:

When complete the instrument will report a scrolling text
message: ‘Calibration successful! Remove gas
from the instrument ––’.

9 Remove the gas from the detector and exit the menu

system.

The instrument is now calibrated.

If the control equipment display requires adjustment, consult the operating
manual for the control display equipment.

Tip

See "Table 4.1" on page 21 for some gases and their typical
range. Please note that detectors can be provided in different
ranges if required.
Contact Crowcon for list of all gases detected.

TXgard-IS+

Calibrating..

Commissioning TXgard-IS+

Issue 7 21

Table 4.1: Typical gas ranges

4.2 Commissioning procedure:

Oxygen detector

Step 1:

Connecting the detector to the control panel
1 Apply power to the detector via 2-way connector J4.

“Figure 1.1” on page 6

The instrument requires a minimum of 8 V dc at connector
J4 at 20 mA.

2 Leave the detector to stabilise for at least 2 hours.

Step 2:

Checking the 4-20 mA loop current
This step can be omitted as the TXgard-IS+ is delivered

pre-calibrated, however, if you wish to check the 4-20 mA loop
current, then it can be checked as outlined below. Alternately
the TXgard-IS+ provides a facility to force a known current
through the loop. Refer to the Ramp mA menu item in
Appendix D for instructions.

Gas Code Gas Unit

Standard Ranges

†

O2 Oxygen %vol 0-25

CO Carbon monoxide ppm 0-250

H2S Hydrogen sulphide ppm 0-25

SO2 Sulphur dioxide ppm 0-10 and 0-100

CL2 Chlorine ppm 0-5

†

Note: other ranges are available on request

Tip

As long as the instrument is running, you can see the supply
voltage on the LCD, by pushing the

 button.

TXgard-IS+ Commissioning

22 Issue 7

NOTE: there is no need to disconnect a sensor when calibrating
mA! The mA control circuit is completely independent from the
gas measuring circuit!

1 Connect a digital voltmeter (DVM) across test points TP1

and TP2 on the baseboard (“Figure 1.1” on page 6 or
“Figure 2.2” on page 9). The loop current flows through a
sense resistor between these test points, so a 4 mA loop
current will show as 40 mV on the DVM, and 20 mA will
show as 200 mV.

Step 3:

Calibrate Oxygen
NOTE: Unlike previous models it is not necessary to manually

“Zero” Oxygen units.

1 Enter the menu system by pressing the  button.

2 At the password prompt enter the password, by default this

is the down button  5 times.

3 You should now be in the main menu

4 Move cursor down and select the Cal O2 @ 20.9% gas

menu. The submenu list for calibrating oxygen appears.

5 Select the Confirm O2 cal menu item. The instrument

will display a scrolling text message: ‘Ensure the

instrument is in clean air and the sensor
has settled’.

TXgard-IS+

To gas display
Inhibit mode

>

Commissioning TXgard-IS+

Issue 7 23

6 Press the  button to start calibrating the detector.

The instrument will display the following message:

When complete the instrument will report a scrolling text
message: ‘Calibration successful’

7 Press the  button to continue and exit the menu system.

The instrument is now calibrated.

If the control equipment display requires adjustment, consult the operating
manual for the equipment.

TXgard-IS+

Calibrating..

TXgard-IS+ Maintenance

24 Issue 7

5 MAINTENANCE

5.1 Routine maintenance

The operational life of the sensors depends on the application, frequency
and amount of gas being seen. Under normal conditions (6-monthly
calibration with periodic exposure to test gas) the life expectancy of the
toxic sensors is 2-3 years, and 2 years for the oxygen sensors.

Site practices will dictate the frequency with which detectors are tested.
Crowcon recommends that detectors be gas tested every month and
recalibrated every six months. To recalibrate a detector, follow the steps in
Section 4.1 (for a toxic gas detector) or Section 4.2 (for an oxygen
detector).

In dusty environments, the detector should be tested more frequently to
ensure that the sensor does not become blocked.

There is no need to recalibrate mA.

5.2 Sensor replacement and servicing of
detectors

To prevent spurious alarms whilst changing sensors, either -

- put the control system into Inhibit mode for this channel (preferred), or

- put the TXgard-IS+ into Inhibit mode (See Appendix D), or

- put the TXgard-IS+ into Ramp mA mode to hold its output at 4 mA or

17.4 mA, as appropriate (typical ungassed toxic / oxygen "safe" signals).

NOTE: Ramp mA or Instrument Inhibit modes might time out before the
sensor settles, so inhibiting at the control panel end is preferable.

5.2.1 Detectors with bayonet type sensor housings

NOTE: There is no need to open the main body of the instrument to

replace these sensors.

Repair of instruments: it is a condition of Certification that damaged
instruments may only be repaired by trained personnel. Whilst
replacement of sensors or personality modules is permitted by
untrained personnel, board-level repairs must be carried out at main
Crowcon offices, which are listed on our website at
www.crowcon.com.

Maintenance TXgard-IS+

Issue 7 25

1. Open the sensor housing by pushing in and turning simultaneously to
release the bayonet fitting and expose the sensor.

2. Remove the sensor from the sensor housing.

3. Fit the replacement sensor, checking the part number is correct. This
part number is labelled on the main body of the detector. Observe the
correct pin alignment with the PCB.

4. Reassemble the sensor housing.

5. The sensor should now be re-zeroed and calibrated.
See “Commissioning” on page 16. For Oxygen sensors see
“Commissioning procedure: Oxygen detector” on page 21).

Fault finding TXgard-IS+

Issue 7 26

6 FAULT FINDING

Fatal errors are severe enough that the gas reading cannot be trusted but can sometimes be cleared by removing power

and reconnecting it. Non Fatal errors are simply warnings that the instrument has noticed a problem, but can continue

/ recover by using backup data.

Symptom / error message Cause Solution

Nothing is displayed - instrument appears

dead

The cause is usually no power, ie the

wires are the wrong way round.

Reverse the polarity by swapping

the wires over. Check supply

voltage.

4-20 mA signal is frozen Instrument outputs a Fault signal Examine display to determine

fault and take action as described

below. Note: the Fault/inhibit

currents can be set to 2, 3, 4, 24

mA or Gas Level in the

Configuration menu (see

Appendix D)

Instrument outputs an inhibit current Instrument is in calibrate mode.

Complete the calibration

operation.

“Supply V High”

“Supply V Low”

The voltage on the 4-20 mA line is too

high (>32 V) or too low (<8 V) for

reliable operation.

Adjust power supply.

Note: some long cables have

significant resistance, and can

supply 8 V at the instrument

terminals at 4 mA, but not 20 mA.

Use the Ramp mA function to

confirm line voltage is OK at 20

mA. (See appendix D)

TXgard-IS+ Fault finding

27 Issue 7

“Temp. low err.”

“Temp. high err”

The temperature is too low or high for

the instrument to work reliably.

Ensure temperature is between –

20°C and +55°C (–4°F to 131°F).

Note: Some sensor types do not

work over this entire range.

“Zero warning” The last zero operation did not succeed

– there would have been a scrolling

message on completion of the zero

operation giving an error whilst still in

the menus

Re-zero sensor. Check sensor is

in clean air and has settled.

“Cal. warning” The last calibration operation did not

complete successfully – there would

also have been a scrolling message on

completion of the calibrate stating that

the operation had failed.

Recalibrate the sensor:

Check the calibration gas is at an

appropriate concentration and is

applied to the sensor at the

correct flow rate 0.5-1.0 litres/

minute.

Sensors have a finite lifetime:

their output gradually decays and

eventually they need replacing.

Occasionally, sensors die

completely, but this normally

requires serious abuse (e.g.

extreme heat, or very high

overloads of gas). Replace

sensor.

Symptom / error message Cause Solution

Fault finding TXgard-IS+

Issue 7 28

“Cal gain error” The signal is very high or low for the

level of gas you are applying. A

scrolling message would have been

displayed on completion of the zero or

calibrate operation giving this fault.

Check you are using the right

level of gas, and that you are

inputting the correct number

through the keypad. Ensure

sensor has been properly zeroed

before calibrating.

“Gas calib. err” (Fatal) Gas calibration data stored in the

sensor module’s non-volatile memory

has been corrupted.

Sensor must be re-zeroed and

calibrated. Without calibration

data the instrument cannot

correctly measure gas.

“mA Calib error” mA calibration data stored in the

instrument’s non-volatile memory has

been corrupted.

mA calibration must be checked,

using the Ramp mA function (see

Appendix D), and re-calibrated or

instrument must be returned to

Crowcon for service.

“FRAM1 fault”

“FRAM2 fault”

FRAMs are non volatile memory. The

instrument has detected corruption in

one. FRAM1 is on the main PCB and

stores the instrument configuration.

FRAM2 is in the Personality Module

and stores sensor data (Calibration

constants, gas name etc.).

Disconnect power and reconnect

it. The FRAM with an error should

restore its data from backup in

the other FRAM.

Alternatively, use the Clear Faults

menu option (see appendix D).

Symptom / error message Cause Solution

TXgard-IS+ Fault finding

29 Issue 7

“mA low error”

“mA high error”

The instrument is recalibrating its

4-20 mA signal, because it has

detected a discrepancy between what it

should be and what it is. This could be

a result of earth loop currents, for

example.

The instrument should finish

correcting the mA signal after a

few minutes. It is deliberately

slow to prevent transient events

giving problems. If the problem

persists, use the Ramp mA menu

item to confirm the instrument is

drawing the current it thinks it is

(see “Appendix D”). The 4-20 mA

signal can be recalibrated if

necessary. If there is still a

problem, check the cable for

ground loops or earthing

problems.

“Amplifier error” (Fatal) Personality module has failed and

needs replacing

“Sensor Fault” (Fatal) Check connections to sensor

have not come loose or have

been incorrectly wired (“Figure

1.1” on page 6)

Alternatively: the instrument

cannot see the sensor. If a worn-

out sensor has just been

replaced, confirm that a new one

has been placed correctly in the

sensor housing.

Symptom / error message Cause Solution

Fault finding TXgard-IS+

Issue 7 30

Error and Fault messages will remain on the operator display panel until they are cleared. Selecting Clear Faults

from the menu will remove them. However, if the fault re-occurs the fault message will be displayed again.

Fault current can be configured to be different for Fatal / Non Fatal events, see Appendix D.

mA is unexpectedly low for gas reading The instrument gas calibration is not

set to the correct scale, for example,

expected range is 0-25 ppm, range

may be set at 0-50 ppm

Recalibrate instrument.

The sample gas is half scale Check the full scale reading

required for example,

0-50 ppm, and the sample gas

value, for example, gas is

supplied as 25 ppm

Unstable mA or gas reading Re-zero and re-calibrate

instrument

Calibration is difficult whilst applying gas,

numbers alter too fast when using up and

down arrows

Personality module contains data for

different unit

Re-zero and re-calibrate. You

may need to perform this

procedure twice to reach a stable

reading

Display contrast poor Wrong contrast setting Check and reconfigure contrast

setting in Configuration menu

Display blank/cannot be read at any angle Faulty circuit, LCD or extremely poor

contrast setting

Send to Crowcon for

reconfiguration

Symptom / error message Cause Solution

TXgard-IS+ Appendix A

31 Issue 7

APPENDIX A

WIRING THE TXGARD-IS+ TO CROWCON
CONTROL EQUIPMENT

This appendix describes how to connect the TXgard-IS+ to the following
Crowcon control panels: Vortex, Gasmonitor, Gasmaster and Gasflag. The
instructions for connecting the cards and setting the links are outlined
below. Connection details for the Ditech range of control equipment will be
included on the wiring diagrams supplied for the system.

Connecting the TXgard-IS+ to a Crowcon Vortex

The TXgard-IS + is connected to the Vortex control panel using a Quad
Channel Module, see “Figure A.1”. The module consists of four channels,

each with a 3-way connector. The detector may be connected to any of the
four channels shown in “Figure A.1”.

Figure A.1: Quad Channel Module

NOTE: Vortex has certain current levels hard-wired as signals.

However,

TXgard-IS+ is highly configurable and can be programmed to
work with most control panels. When connecting to a Vortex, set the
TXgard-IS+ as follows:

Fatal and Non Fatal Fault Currents = "3 mA"
Inhibit current = “24 mA” or "Clean air level".
The latter is better for long cable runs (less IxR drop).

Channel 1

Channel 2

Channel 3

Channel 4

Detector
type
switches

Module
selection

-

+

-

+

Wires use
left hand two
positions

-

+

Wires use
right hand two
positions

+

-

Appendix A TXgard-IS+

Issue 7 32

Set the Detector Type Switch for the appropriate channel to position 2. The
switch can be found in the hatch on the side of the Quad Channel Module,
see “Figure A.1”.

Connecting the TXgard-IS+ to a Crowcon Gasmonitor

The TXgard-IS+ is connected to the Gasmonitor control panel via an
INPUT/OUTPUT MODULE at the rear of the Gasmonitor racking system.
The links for Toxic and Oxygen detectors are the same, configure the

INPUT card as follows:

LINK Make these

connections

LK1 A, C
LK2 E, I, K
LK3 none
LK4 “4-20”
LK5 “24V”
LK6 “C/C”
LK7 “24V”

At the rear of the Gasmonitor, connect the instrument to the INPUT/
OUTPUT MODULE, the section labelled DETECTING HEADS (See
"Figure A.2"). Choose the channel matching the input card.

The module consists of three rows of 16 channels, the terminals to use are
marked 60-107. The top row (terminals 50-55) is not used with the TXgard­IS+. The second row provides 24 V, the third row provides 0 V. The first
two terminal blocks are reserved. The remaining 16 channels marked 1-16
can be used to connect the TXgard-IS+, for example, to connect channel
2, connect the positive wire to terminal 64 and the negative wire to terminal

63. "Figure A.2" shows a TXgard-IS+ connected to channel 2.

NOTE:

Gasmonitors will only recognise a 24 mA signal from

TXgard-IS+ as Fault. Although Gasmonitors can also be configured
to use "less than 2mA" as a Fault signal, the minimum current that
the TXgard-IS+ can draw is 2.2 mA, so TXgard-IS+ will not trigger
Gasmonitor's Fault if the TXgard-IS+ Fault signal is set to
'minimum' (2.2 mA).

TXgard-IS+ Appendix A

33 Issue 7

Figure A.2: Electrical connections for Gasmonitor

Connecting the TXgard-IS+ to a Crowcon Gasmaster

The TXgard-IS+ is connected to a Gasmaster control panel as shown
below. The Gasmaster input channel link should be set to 'SINK' and the
input channel should be configured as 'DET 4-20 SINK'. For hazardous
area installations refer to the Gasmaster manual.

Figure A.3: Electrical connections for Gasmaster

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Channel

0V

24V

60

DETECTOR HEADS

63

66

61

62

64

65

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

SIG

0V

SCR

PWR

­+

TXgard-IS+

Channel Link Settings

FIRE
SINK
SRCE

Safe Area

EXTERNAL BARRIER

4-20 mA Current Sink

Gasmaster

Detector Input

Terminals

Appendix A TXgard-IS+

Issue 7 34

Connecting the TXgard-IS+ to a Crowcon Gasflag

The TXgard-IS+ is connected to the Gasflag via the screw terminals
marked SENSOR +VE (this is the TXgard-IS+ positive supply) and
SENSOR SIG (which connects to TXgard-IS+ negative supply). Set links
LK10A and LK10B to SOURCE, position B.

Figure A.4: Electrical connections for GasFlag

TXgard-IS+ Appendix B

35 Issue 7

APPENDIX B

TXGARD-IS+ SPECIFICATION

Dimensions 160 x 123 x 92 mm (7.3 x 5 x 3.6 inches)

Weight 700 g

Operating voltage 8-32 V dc, loop-powered, 4-20 mA

Normal Output Signal 4-20 mA current sink

Fault current Minimum, 3 mA, 24 mA, or normal gas signal

(configurable)

Operating temperature –40°C to +65°C (–40°F to 149°F)

Note: Instrument operates and has been
certified as Intrinsically Safe between
–40°C and +65°C, giving out a 4-20 mA signal
proportional to measured gas; but LCD will go
blank at about –20°C. The sensor's
performance changes at extremes of
temperature; consult Crowcon if the detector
will be exposed to ambient temperatures below

-20°C or above +40°C

Humidity 15-90% RH, non-condensing for most sensors

Display 2 x 16 character LCD

Response time (typical) (T

90

): approximately 20 seconds for most Toxic

sensors, 10 seconds for Oxygen*

Repeatability ±2% FSD, 6 months*

Cable loop resistance

300

Ω with 22 V supply at 20 mA

Degree of protection IP65 (when fitted with Weatherproof Cap)

Explosion protection Intrinsically Safe

Approval codes

II 1G Ex ia IIC T4(-40°C to +65°)

UL/cUL: Cl I, Div 1 Groups A,B,C,D

Safety certification nos. Baseefa 08 ATEX 0069X, UL E147777

IECEx BAS 08.0028X

"X" Special Conditions for Safe Use: Warning:
Static Hazard Clean Only with a Damp Cloth.

Appendix B TXgard-IS+

Issue 7 36

Standards EN60079-0 (safety in flammable atmospheres)

EN60079-11 (intrinsic safety)
EN50022 (emissions)
IEC61000-4 (immunity)
EN50270 (EMC for gas detection equipment)
EN50271(software design standard)
UL (UL913 Ed 7)
cUL (CSAC22.2 No.157) class 1 group A,B,C
and D

This device complies with part 15 of the FCC
Rules. Operation is subject to the following two
conditions: (1) This device may not cause
harmful interference, and (2) this device must
accept any interference received, including
interference that may cause undesired
operation.

This Class A digital apparatus complies with
Canadian ICES-003.

Cet appareil numérique de la classe A est
conforme à la norme NMB-003 du Canada.

Zones ATEX/IECEx: 0, 1 & 2

UL: Class 1

Gas groups ATEX/ IECEx: IIC

UL: A,B,C & D

Zener barriers or
galvanic isolators

Max 28 V; 93 mA 0.66 Watts

*Specifications are typical, and may vary for different sensor types.

TXgard-IS+ Appendix C

37 Issue 7

APPENDIX C

SPARE PARTS AND ACCESSORIES

Please contact Crowcon for details of the latest replacement sensors.
Please quote the part number given on the "Sensor Replacement label"
mounted on the outside of the sensor housing.

Description Part Number

M20 to ½" NPTF adaptor M02125

M20 to ¾" NPTF adaptor M02281

Ceiling mounting bracket M01401

Collector cone C01051

Spray deflector C01338

728 Zener barrier for use with 24 V dc
systems

C03221

5041 Galvanic isolator C03278

Mounting box for 2 Zener barriers C03224

Mounting box for 5 Zener barriers C03225

Mounting box for 12 Zener barriers C03226

Mounting box for 4 galvanic isolators C01560

Mounting box for 8 galvanic isolators C01561

Calibration gas Contact Crowcon

Bayonet sensor housing 3-wire S01343

Bayonet sensor housing 2-wire (oxygen
sensor)

S012027

Appendix D TXgard-IS+

Issue 7 38

APPENDIX D

MENU SYSTEM

This section provides greater details for the TXgard-IS+ menu items and is
a supplement to the section “Using the TXgard-IS+ menus” on page 14.
You may wish to refer to the Menu Map on the back cover to familiarise
yourself with the menu hierarchy.

This appendix also works in conjunction with the Fault Finding guide on
page 26.

To enter the TXgard-IS+ Menu System

Press the  button and then the default password which is the down
button five times.

To select a menu item use the UP  and DOWN  buttons to move the
cursor ‘ >‘ to the desired menu item and press the  button.

Inhibit mode

Description: Forces instrument to output the Inhibit current.

This menu option provides a convenient option to allow an engineer to
force the instrument to output the Inhibit current whilst he carries out
maintenance on the TXgard-IS+. This will prevent unwanted alarms being
seen at the control panel whilst, for example, the sensor is changed. It
provides an alternative to setting the instrument into Calibrate mode which
also outputs the Inhibit current.

Instructions

1. Enter the TXgard-IS+ menu system by pressing the  key followed by
the down key  five times.

2. Move the cursor down and select the Inhibit mode menu item. By

selecting Enable Inhibit mode the detector output will be forced to a
level set in the Set Inhibit mA menu. “Inhibit” will then be shown
on the normal gas level display. Inhibit mode will time-out after five
minutes, or can be manually reset using the inhibit mode option.

TXgard-IS+ Appendix D

39 Issue 7

The display should look as follows;

Gas Calibration Menus

Description: The gas calibration menus provide the instructions and means
to calibrate the instrument. This menu is different for toxic detectors and
oxygen detectors.

The Toxic detector has two menu items, one to zero the unit and the other
to set the calibration gas level. The oxygen detector has only one menu
item to set the oxygen level. It is not required to manually zero an oxygen
detector.

See Sections 4.1 and 4.2 for detailed step-by-step instructions for using
these menus.

Menu: (Toxic detectors)

Zero/Cal gas

Submenu

To main menu
Zero gas
Calibrate gas

Zero gas

This menu provides instructional guidelines to zero an instrument.

Calibrate gas

This menu provides instructional guidelines to calibrate the gas on the
instrument.

Menu: (Oxygen detectors)

Cal O2 @ 20.9% gas

Submenu

To main menu
Confirm O2 cal

Cal O2 @ 20.9% gas

This menu provides instructional guidelines to set the oxygen level on an
oxygen detector. Note: clean air is always considered to be 20.9% oxygen.

TXgard-IS+

Inhibit active
Press to go on

Appendix D TXgard-IS+

Issue 7 40

Ramp mA output

Description: This menu item allows you to force the output loop current
to a known value. It does not calibrate the 4-20 mA loop current or affect

any calibration values within the TXgard-IS+ detector.

The TXgard-IS+ provides convenient test points within the instrument to
measure the loop current. The test points TP1 and TP2 can be found on
the baseboard (“Figure 1.1” on page 6 and "Figure 2.2" on page 10). The
loop current flows through a sense resistor between these test points, so a
4 mA loop current will show as 40 mV on the DVM, and 20 mA will show
as 200 mV.

When would I use it?

Ramp mA output can be used to help calibrate and set up the control
panel used with a TXGard-IS+ detector by forcing a known current

through the loop. It is also useful for locking the output to a known level
which will not trigger alarms whilst, for example, changing the sensor.

It is also useful if you suspect the current is no longer calibrated. In this
case it can be checked at test points TP1 and TP2.

It is useful during installation to force the loop current to the
maximum value (20 or 24 mA, depending on configuration). The installer

can then confirm line voltage is at least 8 V at the instrument terminals at
maximum current, even with maximum voltage drops in the loop.

Instructions

1. Enter the TXgard-IS+ menu system by pressing the  key followed by
the down key  five times.

2. Move the cursor down and select the Ramp mA output menu item by

pressing . The display should look as follows;

NOTE: The display shows the loop current and the voltage on the
4-20 mA line at the detector. The voltage will fall as the instrument
takes more current due to the voltage drops in the Zener barrier and

TXgard-IS+

mA: 4.0 (22.7V)
Use , to edit

TXgard-IS+ Appendix D

41 Issue 7

cable. The voltage must remain greater than 8 V at the instrument
terminals for the instrument to function.

3. Use the UP  and DOWN  keys to adjust the loop current value.

The current value will increment in 0.5 mA steps. The default value of
the loop current when the menu is first entered is 4 mA. The loop
current can be forced to 24 mA or reduced to 3.5, 3.0 and Minimum
output. Press the  key when finished.

NOTE: on oxygen detectors, a signal of 4 mA is likely to generate a low
oxygen alarm at the control equipment.

4. Exit the menu system.

Configuration

The TXgard-IS+ detector provides a configuration menu to set various
options. Below is a list of options, the values that can be set and a
description.

Menu:

Configuration

Submenu

To main menu
Limit 4-20 mA
Set inhibit mA
Zero suppress
Damping
Menu timeout
Fatal mA
Non-fatal mA
Display option
LCD Contrast
Pwr-on inhibit
Help screen

Appendix D TXgard-IS+

Issue 7 42

Menu item Options Description

To Main Menu Exit Exit to main menu.

Limit 4-20 mA Enable / Disable If enabled, the instrument will only

ever draw a maximum of 20 mA,
no matter what the gas value.

Set inhibit mA Minimum, 3 mA,

Clean Air mA, or
Gas Level

When the instrument is in inhibit
mode or calibration mode, the
instrument outputs an inhibit
current to prevent false alarms
whilst gas is applied. When inhibit
current value is set to ‘Gas Level’
the loop current is not inhibited.

Zero suppress None, Minor or

Major

Defines the size of the dead band
about the zero point of the device.
This will suppress unwanted
spurious signals and improve
stability at zero.Suppression may
be set to 3 levels, with increasing
levels of suppression.

Damping None, Light,

Medium or Heavy

Damping is the means where
noisy gas readings may be
smoothed out. However,
increasing the amount of damping
in order to reduce the amount of
noise will be at the expense of
sensor response time.

Menu timeout 30 secs, 1, 5 or 10

minutes/ No
timeout

This sets the timeout value before
a menu display will automatically
return to the normal display mode
if there is no response or input
from the user. ‘No timeout’ will
disable the timeout option.

Fatal mA Minimum, 3 mA,

24 mA or Gas
Level

This selects the current the
instrument will sink when a fatal
error has been detected. Note:
the option ‘gas level’ is available;
this means the instrument will
ignore the error for the purposes
of loop current - a display
message will still flash as normal.

TXgard-IS+ Appendix D

43 Issue 7

Menu item Options Description

Fatal mA Minimum, 3 mA,

24 mA or Gas
Level

This selects the current the
instrument will sink when a fatal
error has been detected. Note:
the option ‘gas level’ is available;
this means the instrument will
ignore the error for the purposes
of loop current - a display
message will still flash as normal.

Non-fatal mA Minimum, 3 mA,

24 mA or Gas
Level

This selects the current the
instrument will sink when a non
fatal error has been detected.
Note: the option ‘gas level’ is
available; this means the
instrument will ignore the error for
the purposes of loop current - a
display message will still flash as
normal.

Display option No display, Normal

display, mA
display,

This selects what information is
displayed on the normal gas
display screen. ‘Normal’ means
the gas level and flashing ‘OK’ is
displayed, ‘mA display’ also
displays the loop current and ‘no
display’ suppresses all
information.

LCD Contrast Contrast

adjustment

Pressing the up and down arrows
will increase and decrease the
display's contrast. Pressing
RETURN [copy in symbol from
cell above] will return to last
menu.

Pwr-on inhibit Enable / disable Selects whether the detector

output is automatically inhibited
for 30 seconds after power-up.
The output current level while in
inhibit mode is set using the

Set

Inhibit mA

menu.

Help screen Enable / disable If further help is enabled, the

menu will display more detailed
help messages. The user will be
presented with “For error help
press

, else RETURN ”, if a

warning message is displayed.

Appendix D TXgard-IS+

Issue 7 44

Calibrate mA

Description: The Calibrate mA menu provides a means of re-calibrating the
4-20 mA loop current.

NOTE: The TXgard-IS+ detectors leave the factory with the 4-20 mA signal
correctly calibrated. This menu is provided for Service Engineers to adjust
the calibration to match site control equipment which cannot itself be
correctly calibrated.

Menu:

Calibrate mA

Submenu

To main menu
Calibrate 4 mA
Calibrate 20 mA

Instructions

The TXgard-IS+ detector provides two test points to measure the signal
current. Connect a Digital Volt Meter (DVM) across the test points TP1 and
TP2. (“Figure 2.2” on page 10.) The loop current flows through a sense
resistor between these test points, so a 4 mA loop current will show as
40 mV on the DVM, and 20 mA will show as 200 mV.

1. Enter the TXgard-IS+ menu system by pressing the  key followed by
the down key  five times.

2. Move the cursor down and select the Calibrate mA menu item. You
are now in the Calibrate mA submenu.

3. Move the cursor down and select the Calibrate 4 mA menu item.
The display should look as follows;

4. Use the UP  and DOWN  keys to adjust the voltage reading on
the DVM as required across the test points TP1 and TP2 (nominally
40 mV). Press the  key when finished.

TXgard IS+

Use , to set
4mA and press

TXgard-IS+ Appendix D

45 Issue 7

5. To calibrate the 20 mA, select the Calibrate 20mA menu item and
repeat step 4 adjusting the voltage reading to 20 mA value (nominally
200 mV). Press the  key when finished.

6. Exit the menu system.

Clear Faults

Description: Clears Faults from display and unit.

When the TXgard-IS+ detects a fault, a warning message will be displayed
on the operator display panel. Refer to the Fault Finding guide on page 26
to determine cause and solution to the fault.

For example, if an instrument detects the line voltage dropping below
8 V, it will flash the warning: Supply voltage low even if the supply voltage
recovers, to warn you that there was a problem with the supply.

To clear a warning message from the TXgard-IS+ detector

To clear the warning message, enter the TXgard-IS+ menu system, move
the cursor down and select Clear faults menu item and press the 
key.

NOTE: Error and Fault messages will remain on the operator display panel
until they are cleared. Selecting Clear Faults from the menu will
remove them, however, if the fault re-occurs the fault message will be
displayed again

S/W version

Description: this menu item displays the software version of the detector.

Serial number

Description: this menu item displays the serial number of the detector.

Appendix E TXgard-IS+

Issue 7 46

APPENDIX E

4-20 mA LOOPS

A 4-20 mA loop is a standard method of connecting remote instruments to
a control panel.

The basic concept is that a reading of zero gas corresponds to 4 mA, and
full scale gas corresponds to 20 mA.

The control panel supplies typically 24 volts down 2 wires, and measures
the current flowing in the loop. The remote instrument, in this case a gas
detector, controls the current:

The constant 4 mA is used to run the instrument processor, amplifier etc.
This is termed a loop powered, current sink circuit. In this case, the
control equipment is providing (or sourcing) the current and the detector is
receiving (or sinking) the current. The detector is consequently termed a
current sink and the control equipment must be configured to act as a
current source.

Figure E.1

Current loops are often more resistant to radio frequency interference than
a simple voltage reading, and they will generally work down long cables
(e.g. over a kilometre). When using current loops, care must be taken that
the voltage drop of the maximum signal (usually 20 mA) down the line does
not reduce the line voltage below 8 V, which is the minimum working
voltage of the TXgard-IS+. See section 2.3 for further information on
cabling requirements.

NOTE: It is also possible to have 3-wire current loops. In this case, the
instrument is powered by one pair of wires (+ supply and 0 V) and the

TXgard-IS+ Appendix E

47 Issue 7

current signal is measured between the third wire and 0V. Because 3-wire
circuits don’t depend on the current in the signal loop to power them, they
can also source current. However, they require more expensive Zener
barriers to make them intrinsically safe, and cannot be retrofitted into
existing 2-wire installations without replacing the cabling.

Appendix F TXgard-IS+

Issue 7 48

APPENDIX F

CABLING REQUIREMENT

Cabling to TXgard-IS+ must be in accordance with the recognised
standards of the appropriate authority in the country concerned, and must
also meet the electrical requirements of the detector. Crowcon
recommends the use of 2-core twisted pair cable, but there is no particular
restriction as long as it can supply 8 V at 20 mA to the instrument. Suitable
weatherproof glands must be used. Cable should be identified as being
intrinsically safe by some means, for example, by having a blue sheath.
Alternative cabling techniques, such as steel conduit, may be acceptable
provided that appropriate standards are met.

TXgard-IS+ requires a dc supply of 8-32 V and is loop powered.
(If mounting in a hazardous area, do not use a higher voltage than the
Zener barrier’s rating, usually 28 V). Ensure there is a minimum supply of
8 V at the detector, taking into account the voltage drop due to cable
resistance and the sense resistance of the control panel to which it is
connected.

For example, a nominal dc supply at the control panel of 24 V has a
guaranteed minimum supply of 18 V. The circuit may demand up to 24 mA
(see note 1). Given a sense resistor in the control panel of 250 Ω (dropping
6 V at 24 mA) the maximum voltage drop allowed due to cable resistance
is 18-8-6 = 4 V. Thus the maximum loop resistance allowed is 4 V/24 mA
= 166 Ω (approximately).

Safe installation (only relevant for installations in
Hazardous Areas):

TXgard-IS+ depends on the principle of Intrinsic Safety to prevent
explosions. This means that the energy stored in the instrument never
reaches a level which could cause a dangerous spark capable of igniting
gas. Since some energy is stored in the cable, the installation must
consider the safety of the entire system: Barrier + Cable + Instrument.
Fortunately, the calculations are quite straightforward.

Connection to the safe area is via a zener barrier or galvanic isolator. The
barrier or isolator will have a maximum permissible set of L, C and perhaps
L/R values printed on it. Example:

MTL type 728 barrier

V

oc

<=28.12 V, Isc <= 93 mA, Ca <= 0.083 uF, La <= 3.05 mH

TXgard-IS+ Appendix F

49 Issue 7

This means that the barrier output will not exceed 28.12 V or 93 mA into
the Hazardous Area, due to the barriers' internal clamps and fuse. At these
power levels, you can attach up to 0.083 microfarads of capacitance and

3.05 millihenries of inductance and still be safe.

Example: unsafe: a 1 microfarad load would store enough energy (0.5 x C
x V2) to potentially cause a spark capable of igniting gas.

TXgard-IS+ has been designed to have as low a capacitance and
inductance as possible, to permit it to be cabled up with several kilometres
of cable.

Example:

You must refer to the cable specification to discover the exact values of
capacitance and inductance.

* In this example, the total inductive load on the output of the zener barrier
is 870 uH which is well below its 3,050 uH limit.

* The capacitive load is only 60.1 nF which is below the 83 nF limit of the
barrier. So the system is Intrinsically Safe.

In addition to the safety of the system you must also consider: will it work?
As described earlier in Appendix F, you must check that the TXgard-IS+
will get a minimum supply of 8 volts at the end of the cable. Here we can
count on 22 V at the control panel, and with a maximum current drain of
20 mA, we will lose (250 + 300 + 36.2 ohms) x 0.02 amps = 11.7 V, so the
detector will always have at least 10.3 V. However, we have to ensure it
does not have its fault current set to "24mA" or it will only get 7.9 V. For
longer cable lengths, use cable with 1.5 or 2.5 mm

2

cores (see section 2.3

for resistance values).

Note 1. You might only need to allow for up to 20 mA, depending on how the
instrument is configured. The signal can be limited to the range 4-20 mA using the
"Limit -20 mA" option in the Configuration menu (see "Appendix D"). Otherwise the
instrument increases signal (gas) current to a maximum of 24 mA. Fault and Inhibit
currents can be programmed to be 24 mA in the Configuration menu if desired, but
most control panels use 3 mA or less to signal faults.

Control panel

Zener barrier

1 km of 1 mm cable

2

TXgard-IS+

Nominal 24 V supply
(guaranteed 22 V output)
250 ohm current sense resistor

300 ohm resistance
max permissible load

3.05 mH, 0.083 uF

36.2 ohm (loop)
860 uH, 60 nF
Maximum L/R ratio 25 uH/ohm

10 uH, 0.1 nF
(safety information
is marked on label)

Safe Area

HazardousArea

Appendix F TXgard-IS+

Issue 7 50

Note 2. It is worth noting that most 28 V Zener barriers are 300 Ω, which will give
another 6 V drop. With an 18 V supply and a 250

Ω

sense resistor, this would give

a voltage at the end of an 80

Ω

loop of min. 18 - 6 - 6 - 2 = 4 V, which is not enough
to drive the TXgard-IS+ (which requires 8 V or more). Therefore when using Zener
barriers and high-value sense resistors, ensure the supply voltage is a good 24 V:
thus e.g. 24 - 6 - 6 - 2 = 10 V. Obviously if you have configured the instrument to
draw no more than 20 mA (see Note 1), the situation is improved.

Note 3. By loop resistance we mean the total resistance of both wires in the twisted
pair cable, that is, one wire going to the detector and one returning. For example,
an 80

Ω

loop resistance will be 40 Ω out and 40 Ω back. Cable resistance values are
usually quoted for a single conductor, thus the value has to be doubled to correctly
calculate the loop resistance.

Appendix G TXgard-IS+

Issue 7 51

APPENDIX G

SENSOR LIMITATIONS

The sensors used in TXgard-IS+ have limitations common to all such gas
sensors, and users should be aware of the points listed below. Crowcon
can advise on particular situations and suggest alternative sensors if the
instrument is likely to experience extreme conditions.

• Electrochemical gas sensors contain chemicals. The
chemicals' performance changes at extremes of temperature;
consult Crowcon if the detector will be exposed to ambient
temperatures below -20°C or above +40°C.

• Extreme levels of humidity can also cause problems. The
sensors are rated for an (average) ambient of 15-90% R.H.
However they are used from the tropics to deserts to tundra
without this normally being a problem.

• Water should not be allowed to collect on the sensor as this
may impede gas diffusion. This is why the sensors are usually
mounted on the bottom of the instrument.

• Persistent exposure to high levels of toxic gas will shorten the
life of the sensor. If the high level gas is corrosive (e.g.
hydrogen sulphide) damage may occur over time to metal
components.

• Sensors may be cross sensitive to other gases. If unsure,
contact Crowcon or your local agent.

• When used in dusty environments, detectors should be
inspected regularly as dust may block the sensor and prevent
gas from being detected.

Warranty Statement

This equipment leaves our factory fully tested and calibrated. If within the warranty
period, the equipment is proved to be defective by reason of faulty workmanship
or material, we undertake at our discretion either to repair or replace it free of
charge, subject to the conditions below.

Warranty Procedure

To facilitate efficient processing of any claim, contact our customer support team
on [phone] with the following information:

Your contact name, phone number, fax number and email address.
Description and quantity of goods being returned, including any
accessories.
Instrument serial number(s).
Reason for return.

TXgard-IS+ Fault finding

52 Issue 7

Obtain a Returns form for identification and traceability purpose. This form may be
downloaded from our website 'crowconsupport.com', along with a returns label,
alternatively we can 'email' you a copy.

Instruments will not be accepted for warranty without a Crowcon Returns
Number ("CRN"). It is essential that the address label is securely attached
to the outer packaging of the returned goods.

The guarantee will be rendered invalid if the instrument is found to have been
altered, modified, dismantled, or tampered with. The warranty does not cover
misuse or abuse of the unit.

Any warranty on batteries may be rendered invalid if the use of an unauthorized
charger is proven. Non-rechargeable batteries are excluded from this warranty.

Warranties on sensors assume normal usage, and will be rendered invalid if the
sensors have been exposed to excessive concentrations of gas, extended periods
of exposure to gas or have been exposed to 'poisons' that can damage the sensor,
such as those emitted by aerosol sprays

Warranty Disclaimer

Crowcon accept no liability for consequential or indirect loss or damage
howsoever arising (including any loss or damage arising out of the use of the
instrument) and all liability in respect of any third party is expressly excluded.

This warranty does not cover the accuracy of the calibration of the unit or the
cosmetic finish of the product. The unit must be maintained in accordance with the
Operating and Maintenance Instructions.

The warranty on replacement consumable items (such as sensors) supplied
under warranty to replace faulty items, will be limited to the unexpired warranty of
the original supplied item.

Crowcon reserves the right to determine a reduced warranty period, or decline a
warranty period for any sensor supplied for use in an environment or for an
application known to carry risk of degradation or damage to the sensor.

Our liability in respect of defective equipment shall be limited to the obligations set
out in the guarantee and any extended warranty, condition or statement, express
or implied statutory or otherwise as to the merchantable quality of our equipment
or its fitness for any particular purpose is excluded except as prohibited by statute.
This guarantee shall not affect a customer's statutory rights.

Crowcon reserves the right to apply a handling and carriage charge whereby units
returned as faulty, are found to require only normal calibration or servicing, which
the customer then declines to proceed with.

For warranty and technical support enquiries please contact::

Customer Support

Tel [phone]
Fax [phone]
Email '[e-mail]'

MAIN MENU

To gas display

Inhibit mode

Ramp mA output

Configuration

S/W version

Serial number

Calibrate mA

Clear faults

Zero/cal gas

(cal O2 @ 20.9% gas)

Inhibit mode

Forces instrument

to output Inhibit

current

Clear faults

Clears faults

from display

and unit

Calibration of

zero gas

and sensed

gas

Zero / Cal gas

To main menu

Zero gas

Calibrate gas

Submenu

Calibration of

20.9% gas

Cal O2 @ 20.9% gas

To main menu

Confirm O2 cal

Submenu

Calibration of

4-20mA loop

current

To main menu

Calibrate 4mA

Calibrate 20mA

Calibrate mA

Submenu

Ramp mA output

Manual ramp

of mA output

Configuration

To main menu

Limit 4-20mA

Set inhibit mA

Zero suppress

Damping

Menu timeout

Fatal mA

Non-fatal mA

Display option

Pwr-on inhibit

Help screen

LCD Contrast

Submenu

Display shows

two lines of the

menu list at a

time, use DOWN

key to display

other menu items

Serial number

Displays

serial number

S/W version

Displays

software version

Toxic detectors

Oxygen detectors

To enter Main Menu press ENTER

key then DOWN key 5 times

NORMAL DISPLAY

To gas display

Inhibit mode

TXgard-IS+

0 ppm

4.0mA

CO

OK

-

Contactos/Contacts:

Comercial/Commercial:

Fernando Mena Costa

e-mail: fcosta@bhb,pt

Tel: [phone]

Fax: [phone]

Assistência/Service:

Patricia Costa

e-mail: [e-mail]

Tel: [phone]