ATI Technologies A12-17 Operation And Maintenance Manual

O & M Manual

A12-17

Combustible Gas Transmitter

Home Office European Office

Analytical Technology, Inc. ATI (UK) Limited
6 Iron Bridge Drive Unit 1 & 2 Gatehead Business Park
Collegeville, PA 19426 Delph New Road, Delph
Phone: [phone] Saddleworth OL3 5DE
610-917-0991 Phone: [phone]
Fax: [phone] Fax: + 44 (0)1457-874-468
Email: [e-mail] Email: [e-mail]
Web: www.Analyticaltechnology.com

Fax: [phone] Fax: + 44 (0)1457-874-468

A12-17 Combustible Gas Transmitter

TABLE OF CONTENTS

INTRODUCTION ................................................................................................................................................................. 3

SPECIFICATIONS ............................................................................................................................................................... 7

INSTALLATION .................................................................................................................................................................. 8

SENSOR LOCATION ........................................................................................................................................................10

INTERFERENCES ............................................................................................................................................................10

ELECTRICAL CONNECTIONS – TRANSMITTER .......................................................................................................11

DUAL CONDULET SYSTEM ..........................................................................................................................................13

A12-17 TO B14 CUSTOMER WIRING DIAGRAM.........................................................................................................15

A12-17 TO GENERIC INSTRUMENT WIRING DIAGRAM ..........................................................................................16

OPERATION ........................................................................................................................................................................17

START-UP .........................................................................................................................................................................17

START-UP DELAY ...........................................................................................................................................................18

FRONT PANEL MAGNETIC CONTROLS ......................................................................................................................18

LIQUID CRYSTAL DISPLAY ..........................................................................................................................................19

MENU SEQUENCE ...........................................................................................................................................................20

Figure 14 cont’d - Transmitter Program Chart ............................................................................................................21

TRANSMITTER MODE SELECTION .............................................................................................................................22

INFORMATION MODE ....................................................................................................................................................22

TEST MODE ......................................................................................................................................................................22

MANUAL AUTO-TEST ACTIVATION ...........................................................................................................................22

ANALOG OUTPUT SIMULATION .................................................................................................................................23

CALIBRATION ...................................................................................................................................................................24

ZERO ADJUSTMENT .......................................................................................................................................................24

SPAN ADJUSTMENT .......................................................................................................................................................25

MA OUTPUT ADJUSTMENT ...........................................................................................................................................26

AUTO-TEST ENABLE/DISABLE SELECTION (UNITS WITH AUTO-TEST) ...................................................................26

CALIBRATION FOR OTHER COMBUSTIBLE GASES ................................................................................................27

SENSOR RESPONSE TEST ..............................................................................................................................................27

ERROR MESSAGES ........................................................................................................................................................28

SENSOR REPLACEMENT ...............................................................................................................................................29

SPARE PARTS LIST ...........................................................................................................................................................30

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A12-17 Combustible Gas Transmitter

TABLE OF FIGURES

FIGURE 1 - TRANSMITTER COMPONENTS ............................................................................................. 5

FIGURE 2 - TYPICAL SYSTEM DIAGRAM ................................................................................................. 6

FIGURE 3 - GAS TRANSMITTER DIMENSIONS, NO AUTO-TEST ........................................................... 8

FIGURE 4 - GAS TRANSMITTER DIMENSIONS, WITH AUTO-TEST ....................................................... 9

FIGURE 5 - TRANSMITTER CONNECTIONS, NO AUTO-TEST.............................................................. 11

FIGURE 6 - TRANSMITTER CONNECTIONS WITH AUTO-TEST ........................................................... 12

FIGURE 7 - DUAL CONDULET CONNECTIONS, SENSOR W/O AUTO-TEST ....................................... 13

FIGURE 8 - DUAL CONDULET CONNECTIONS, SENSOR WITH AUTO-TEST ..................................... 13

FIGURE 9 - DUAL CONDULET TYPICAL INSTALLATION ....................................................................... 14

FIGURE 10 - B14 RECEIVER CONNECTIONS ........................................................................................ 15

FIGURE 11 - GENERIC INSTRUMENT CUSTOMER WIRING................................................................. 16

FIGURE 12 - MODEL A12-17 FRONT PANEL .......................................................................................... 18

FIGURE 13 - LIQUID CRYSTAL DISPLAY ................................................................................................ 19

FIGURE 14 - TRANSMITTER PROGRAM CHART ................................................................................... 20

FIGURE 15 - CALIBRATION ADAPTER ASSEMBLY ............................................................................... 24

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A12-17 Combustible Gas Transmitter

INTRODUCTION

The model A12-17 is an advanced combustible gas transmitter providing reliable measurement of
combustible gas levels in industrial plant environments. A12-17 transmitters combine catalytic bead type
gas sensors and an electronic amplifier that transmits gas concentration using a standard 4-20 mA signal.
Transmitter electronics provide a local LCD display of gas concentration and contain magnetic controls to
allow testing and calibration without opening the enclosure. Typical applications are ambient air
monitoring near process tanks or piping, or in enclosed spaces where combustible gases may leak or
accumulate.

The A12-17 transmitters are composed of two main parts, the gas sensing element and the
electronic transmitter. The sensor is an explosion-proof assembly made of type 316 stainless steel with a
flame arrestor bonded at the sensing end. The electronic transmitter is a plug-in module housed in an
explosion-proof cast aluminum housing with an epoxy powder coating suitable for areas designated Class
I, Groups B, C, & D; Class II, Groups E & F, and Class III. Sensors are normally screwed directly into the
transmitter enclosure and connected with a short cable. However, sensors can be mounted remote from
the transmitter up to 50 feet, provided that sensor cables are properly protected in explosion-proof
conduit.

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A12-17 Combustible Gas Transmitter

VIA THE RELAY PLUG MOUNTED ON THE BOTTOM

1 3/8

” FLATS

A12-17 TRANSMITTER MODULE

¾” NPT

1¼” NPT

EXPLOSION-PROOF ENCLOSURE

RELAY BASE

WALL MOUNT BRACKET

PLUG TRANSMITTER MODULE INTO THE RELAY BASE
OF THE TRANSMITTER MODULE.

¾” NPT

C10-17 COMBUSTIBLE SENSOR

¾” NPT

C28-17 COMBUSTIBLE SENSOR
WITH AUTO-TEST

1/8” TUBE I.D., BARB FITTING

1¼” NPT

SPLASH GUARD (00-0789)

Figure 1 - Transmitter Components

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A12-17 Combustible Gas Transmitter

A12-17 TRANSMITTER

Model A12-17 transmitters are available with a unique sensor verification system called Auto-Test.
This option consists of a miniature gas generator incorporated into the explosion-proof sensor assembly
which automatically generates a combustible gas every 24 hours. The gas generator function is
controlled by the microcontroller in the transmitter electronics. When activated, the generator will provide
a true gas test of the combustible gas sensing element, and will automatically alert operators to sensor
problems that might develop due to sensor poisoning or coating. Figure 1 shows both a standard sensor
and a sensor equipped with the Auto-Test generator.

The Auto-Test feature provides daily verification of sensor response. While it is not intended to
replace calibration, the automatic sensor test greatly reduces the amount of manual testing required to
assure that the gas detection system is functioning properly. Should a sensor fail to respond to the gas
test, the 4-20 mA signal from the transmitter is locked at 3 mA, providing a trouble signal to any receiving
equipment.

A typical installation for the A12-17 is shown in Figure 2 below. It is shown connected to ATI’s series
B14 single channel receiver, but the transmitter may be used directly with PLC, DCS, or computer
monitoring systems without the use of a special receiver.

4-20mA OUTPUT

POWER, 85-255 VAC or VDC

C28-17 GAS SENSOR WITH AUTO-TEST
(SHOWN WITH SPLASH GUARD)

(3) SPDT, 10A, ALARM RELAYS

(1) SPDT, 10A, TROUBLE RELAY

3 COND. 20 AWG UNSHIELDED OR SHIELDED CABLE

Figure 2 - Typical System Diagram

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A12-17 Combustible Gas Transmitter

SPECIFICATIONS

Range: 0-100% LEL (Lower Explosive Limit)
Display: 3 Digit LCD
Response Time (T90): 10 Seconds
Sensitivity: 1% LEL
Zero Drift: < 2%/Month
Power: 12-28 VDC, 12 VDC at 150mA nominal, 200mA max.

24 VDC at 75mA nominal, 100mA max.

Output: 4-20 mA DC, 375 ohms maximum load at 12 VDC

850 ohms maximum load at 24 VDC

1000 ohms maximum load at 28 VDC

Controls: Four magnetic control switches operable through glass window
Temperature Limits: -40° to + 70° C.
Sensor Type: Catalytic bead type, poison resistant
Sensor Option: Auto-Test gas generator
Sensor Materials: 316 Stainless Steel
Transmitter Enclosure: Cast Aluminum with Epoxy Coating, Glass window
Area Classification: NEC Class I, Groups B, C, & D, Class II, Groups E, F & G, Class III
Connections: 3 wire, 20 AWG, 500 feet max. (150 m.)
Sensor Cable Length: Maximum 50 feet for separation between sensor and transmitter
Weight: 4 lbs. (1.4 Kg.)

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A12-17 Combustible Gas Transmitter

INSTALLATION

Combustible gas sensor/transmitters are explosion-proof assemblies that are normally mounted
directly to suitable explosion-proof conduit. To maintain the explosion-proof integrity of the transmitter, a
suitable cable entry seal must be used in accordance with the applicable electrical code.
Sensor/transmitters should be mounted with the sensor facing down as shown in Figure 3 and 4. A12-17
transmitters are also supplied with a mounting bracket that can be used to secure the unit to a wall or
plate.

NOTE: Gas sensors without auto-test are shipped with a protective plastic cap over the end. This cap

should be left in place to avoid damage to the sensor during installation. If the detection system
is to be activated within a few days of installation, the cap should be removed when installation
is complete. Otherwise, leave the cap in place until the system is to be placed in service. Be

sure to leave the protective cap on the sensor if painting is to be done in the area of the
sensor.

CONDUIT ENTRY, ¾” NPT

(ANY CONNECTION MADE MUST

BE WATER-TIGHT,

WALL MOUNT BRACKET

(2) 5/16” DIA. THRU

SECURE BRACKET TO WALL

- HARDWARE IS CUSTOMER
SUPPLIED

¾” NPT

1 1/8” HEX

¾” NPT

C10-17 COMBUSTIBLE SENSOR

Figure 3 - Gas Transmitter Dimensions, No Auto-Test

¾” NPT

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A12-17 Combustible Gas Transmitter

1.75” DIA.

Figure 4 - Gas Transmitter Dimensions, with Auto-Test

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A12-17 Combustible Gas Transmitter

SENSOR LOCATION

Combustible gas sensors are used to detect a variety of gases or vapors. The proper sensor
location will depend on the type of gas is expected. For gases that are lighter than air, such as methane,
sensors should be located near the ceiling. For gases that are heavier than air, such as butane, sensors
should be mounted near the floor. If the gas or vapor has a density near that of air, locate the sensor
about 5 feet off the floor in enclosed areas. Gas sensors mounted outdoors should be located near
anticipated leak sources (valves, flanges, compressors, etc.) and the location will depend on normal wind
patterns and anticipated employee activity areas.

The following are a few common combustible gases, along with their relative density (air = 1.00).
Densities less than one indicate gases that are lighter than air while those with densities greater than one
are heavier than air. Combustible vapors from most solvents, such an Benzene, n-Hexane, Methanol,
Ethanol, and MEK, are heavier than air and will tend to accumulate near the floor in enclosed spaces with
little air movement.

Methane 0.55
Butane 2.11
Propane 1.55
Hydrogen 0.07
Ammonia 0.60

INTERFERENCES

Combustible gas sensors contain two heated elements. One of these elements is active, and will
allow combustible gases or vapors to burn on its catalytic surface. The other is passive, and does not
react to gases. These two elements form two legs of a Wheatstone bridge measuring circuit. When
combustible gas contacts the sensor, the active element burns this gas and the temperature of this
element increases, changing its resistance. The transmitter measures the imbalance in the bridge circuit
and transmits the data to the receiver for display and alarming purposes.

Combustible sensors are adversely affected by a few compounds that may be present in a given
application. Probably the worst of these are silicone vapors from silicon based lubricants or sealants.
High silicon vapor concentrations can cause complete loss of sensitivity in as little as a few hours. These
sensors should not be used where silicon vapors are normally present, and sensors should be protected
from these vapors if such compounds are in use temporarily.

Lead compounds and high levels of hydrogen sulfide can also cause degradation of combustible
sensors. While lead vapors are not commonly encountered, they can also cause complete sensor failure
if encountered. Hydrogen sulfide will cause reduced sensitivity over the first few weeks of exposure, but
then will level out. The effect of hydrogen sulfide can normally be compensated for by re-calibration after
the first few weeks of use.

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