ADC MGA3000 series Operating instructions

MGA3000

MULTI-GAS ANALYSER

OPERATION MANUAL

MGA3000 Multi-Gas Analyser Operation Manual Iss. 1.00

CONTENTS

Contents ............................................................................................................ 1

1. Introduction ................................................................................................... 1

1.1 About the Instrument .............................................................................................1

1.2 Instrument Identification.........................................................................................1

1.3 The Display & Operating Controls.............................................................................2

1.3.1 The Display ...................................................................................................2

1.3.2 The Operating Controls ...................................................................................2

1.4 Electrical Outputs ...................................................................................................2

1.4.1 Analogue Outputs ..........................................................................................2

1.5 RS232 port............................................................................................................2

1.6 Operating Principles................................................................................................3

1.6.1 Infrared Absorption ........................................................................................3

1.6.2 The Optical Bench In Use ................................................................................3

1.6.3 The Oxygen Sensor in Use ..............................................................................4

2. Installation ..................................................................................................... 5

2.1 Installation Arrangement.........................................................................................5

2.2 Location & Ambient Conditions.................................................................................5

2.3 Power Supply Setting & Connections ........................................................................6

2.3.1 Power Supply Setting......................................................................................6

2.3.2 Power Supply Connections ..............................................................................6

2.4 Serial I/O (RS232C) ...............................................................................................7

2.5 Analogue Outputs ..................................................................................................7

2.5.1 Setting the analogue outputs...........................................................................8

2.6 Alarm (Trip) Outputs ..............................................................................................9

2.7 Gas Arrangements ............................................................................................... 10

2.7.1 The Gas Circuit ............................................................................................ 10

2.7.2 The Sample Gas........................................................................................... 10

2.7.3 The Span Gas .............................................................................................. 11

2.7.4 The Zero Gas............................................................................................... 11

2.7.5 The Exhaust Gas .......................................................................................... 12

2.7.6 Gas Pump(s) ............................................................................................... 12

2.8 Use of Chemicals (certain models only)................................................................... 12

2.8.1 Water Vapour .............................................................................................. 12

2.8.2 Carbon Dioxide ............................................................................................ 13

2.8.3 Precautions ................................................................................................. 13

2.9 Pre-operation Checks............................................................................................ 13

2.10 General Advice................................................................................................... 13

2.10.1 Use of Gas Cylinders................................................................................... 13

2.10.2 Gas Leaks ................................................................................................. 14

2.10.3 Exhausting & Ventilation ............................................................................. 14

3. Setting Up .....................................................................................................15

3.1 Preview............................................................................................................... 15

3.2 On Power Up ....................................................................................................... 15

3.3 Zero & Span Operations........................................................................................ 15

MGA3000 Multi-Gas Analyser Operation Manual Iss. 1.00

3.4 Display & Keypad ................................................................................................. 16

3.4.1 Display ....................................................................................................... 16

3.4.2 Function Keys .............................................................................................. 17

3.4.3 Menus......................................................................................................... 17

3.5 Analogue (Chart) Outputs ..................................................................................... 18

3.6 Alarm (Trip) Outputs ............................................................................................ 18

3.6.1 Setting Alarm Outputs .................................................................................. 18

3.7 RS232C Serial Port............................................................................................... 19

3.7.1 Protocol ...................................................................................................... 19

3.7.2 Serial Port Settings....................................................................................... 19

3.8 Measurement ...................................................................................................... 20

4. Calibration.....................................................................................................21

4.1 Initial Checks....................................................................................................... 21

4.2 Warm Up ............................................................................................................ 21

4.3 Zero Adjustment.................................................................................................. 21

4.3.1 Manual Zero ................................................................................................ 22

4.3.2 Auto Zero.................................................................................................... 22

4.4 Span Adjustment ................................................................................................. 23

4.4.1 Setting Span ............................................................................................... 23

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

5.1 Routine Checks .................................................................................................... 24

5.1.1 Water Vapour .............................................................................................. 24

5.1.2 Dust ........................................................................................................... 24

5.2 Instrument Checks............................................................................................... 25

5.2.1 Source Block Purge (when fitted) ................................................................... 25

5.2.2 Filter Column (when fitted)............................................................................ 25

5.2.3 Sample Flow................................................................................................ 25

5.2.4 Throttles ..................................................................................................... 26

6. Optical Bench Descriptions ..............................................................................27

6.1 Introduction ........................................................................................................ 27

6.2 GC Bench (when fitted)......................................................................................... 27

6.3 SB Bench ............................................................................................................ 28

7. Electrical Specifications ...................................................................................30

7.1 Power Supply ...................................................................................................... 30

7.2 Analogue Outputs ................................................................................................ 30

7.2.1 When set for voltage output .......................................................................... 30

7.2.2 When set for current output .......................................................................... 30

7.3 Alarm (Trip) Contacts ........................................................................................... 30

7.4 Serial (RS 232) Port ............................................................................................. 31

8. Spare Parts ...................................................................................................32

9. Moisture Sensor Option...................................................................................33

9.1 General Description .............................................................................................. 33

9.1.1 MGA3000 Zero Calibration............................................................................. 33

9.1.2 MGA3000 Span Calibration ............................................................................ 33

9.1.3 Sensor Autocal............................................................................................. 33

9.1.4 Pre-conditioning the transmitter..................................................................... 34

9.1.5 Adjust the Auto Cal ...................................................................................... 34

MGA3000 Multi-Gas Analyser Operation Manual Iss. 1.00

9.1.6 Completing the Auto Cal ............................................................................... 34

9.1.7 Faults/Errors................................................................................................ 35

1. INTRODUCTION

IMPORTANT

Before operating the Instrument for the first time, ensure all the relevant installation

checks have been carried out [refer to Section 2.9].

1.1 About the Instrument

The MGA3000 Series Instrument is designed for bench or rack mounting and provides a

measurement of gas concentration according to specific user requirements.

Single, dual or triple gas versions are available utilising one or more IRGA optical benches

and/or chemical cells.

Most instruments incorporate IRGA benches that generate a signal proportional to the infrared

absorption of the measured gas. Providing the gas concentration lies within the designed range

of the instrument, the signal is periodically compared with reference gas (usually at zero and a

convenient mid-span condition). Calibration is achieved manually via simple front panel

controls.

Some instruments may include a chemical cell which reacts with the specific gas and which

provides an electrical output in proportion to the reaction.

Gas concentrations are indicated on a front display panel together with both analogue and

digital signal outputs.

Gas connections to and from the instrument are via suitable fittings on the rear panel. The gas

flow is maintained via an internal sample pump.

The MGA3000's electrical supply can be set at the rear panel to operate from a 110V, 220V or

240VAC mains supply.

1.2 Instrument Identification

Each Instrument is uniquely identified with a Serial Number. This is located on a label on the

rear panel alongside the Model Number for the particular Instrument.

Always quote the serial number and model number in any communications requiring

after sales support.

1.3 The Display & Operating Controls

1.3.1 The Display

The display is a LCD Graphic type that is

illuminated from behind to achieve good

contrast and visibility. Its primary function is

to provide large character readouts of the gas

concentrations together with sample flow

status and key functions.

1.3.2 The Operating Controls

The operating controls are menu driven and

accessed by the 5 keys on the keypad

adjacent to the LCD display. The individual

functions of the keys are clearly labelled on

the display.

Selecting a menu function (by pressing the appropriate key) will cause the function to be

selected, or the next menu to be displayed, as required. In general, the bottom menu key is

used to return to the previous menu, acknowledge a message, or cancel an operation.

1.4 Electrical Outputs

1.4.1 Analogue Outputs

MGA series analysers have up to four analogue outputs, numbered 1 to 4 for connection

purposes. One output is provided for each of the gas channels fitted. When fewer than four

gas channels are fitted, one or more outputs will be inactive or not connected.

Alarm (trip) outputs

Up to five alarm contacts are provided to indicate gas readings above/below/outside user set

concentrations

1.5 RS232 port

An industry-standard serial port is fitted to the rear panel to allow gas readings to be read and

zero to be set by a PC or other computer equipment.

Figure 1 - An example main screen (single gas

model)

1.6 Operating Principles

1.6.1 Infrared Absorption

With the exception of Oxygen, the instrument measures gas concentrations using the effect of

infrared absorption.

All heteroatomic gases absorb (or transmit) light energy in the infrared region at specific

wavelengths that are dependent upon the chemical composition of each type of gas.

Furthermore, the level of absorption is proportional to the mass of the gas present. This

characteristic is utilised in infrared gas analysis (IRGA) benches.

The benches incorporate a source of infrared energy (usually in the form of a heated filament),

which is then optically filtered to reduce the radiation spectrum to that of the absorption band

of the gas being measured.

A pyro-electric detector is used to measure the difference in energy between a reference zero

(no absorption) condition and that after some absorption in the gas has occurred. By

calibrating the bench at the zero condition and a known span concentration, a reliable measure

of concentration over the span range is obtained.

To improve the stability and to assist in the detection process, the infrared source is modulated

mechanically at 3-18hz depending on the type of bench being used.

The relationship between absorption and concentration is not linear. For this reason the non-

linear output from the detector is modified electronically to give a linear output to the chart

recorder and display outputs.

The performance of an IRGA bench is compromised by the presence of 'interference' gases in

the sample. Such gases, of which the most common is water vapour, have an overlapping

infrared response to that of the measured gas and their effects are minimised by careful

filtering and the selection of the absorption band.

The level of absorption measured is relative and therefore an IRGA provides a comparative

measurement, not an absolute one, against 'zero' and 'span' reference gases.

A 'zero' gas has no detectable concentration of the gas being measured. Depending on the

gas, fresh air, chemically stripped air or nitrogen may be used. A 'span' gas has a known

concentration of the measured gas and is used to set the gain (or span) of the analysis in the

mid-range region. Under normal circumstances, the concentration is equivalent to about 80%

of the displayed full-scale reading.

1.6.2 The Optical Bench In Use

In order to obtain and maintain the optimum performance from the instrument, a number of

guidelines are offered associated with the use of the instrument, and, in particular, those

elements under the control of the User.

The IRGA bench is essentially an optical system and can suffer some deterioration in the

performance if it is internally contaminated by the condition of the incoming gases.

The gas sample should be reasonably dry. If the presence of water vapour is or is not expected

it is recommended that the instrument is continuously switched 'ON' to prevent condensation.

The flow rate of the gas sample affects the response time (to change) of the measurement -

the measurement being on average the mix of the sample flowing through the cell. In practice

a sample flow rate of nominally 500 ml/min

provides satisfactory performance for any

instrument. The instrument is fitted with a flow sensor and the flow rate is indicated on the

display. There is a potentiometer and throttle fitted internally that allows this flow rate to be

reset if necessary.

Generally the sample gas will be pumped to achieve the required flow rate. An internal pump is

fitted in the instrument and can be switched on or off via the key labelled ‘pump’ on the front

panel. It is recommended that the pump is switched 'OFF' if the sample lines are being

attended to or the condition of the sample gas is suspect (for example it contains water).

The sample rate is factory pre-set for sample gas at ambient pressure.

The installation of pressurised cylinders must include suitable pressure regulators and carefully

controlled to avoid damage to pump or flow sensor due to over-pressure.

The instrument must be allowed to 'temperature stabilise' after first being switched on. The

display will show a thermometer symbol until the associated bench has reached operating

temperature. The instrument's enclosure plays a role in temperature control as well as

providing protection and the enclosure (top and front) should be securely in place before use.

Unless the instrument is only used occasionally it is advisable to leave the instrument switched

on, particularly over-night when reduced temperatures may result in condensation. In standby

conditions the sample pump should be switched off'.

1.6.3 The Oxygen Sensor in Use

As oxygen does not absorb infrared (it is diatomic), it's measurement is via a chemical oxygen

sensor. This operates in a similar way to a battery in that a voltage is generated between two

plates immersed in electrolyte. The sample gas is passed over a membrane which allows

oxygen molecules to pass through it into the electrolyte, stimulating the reaction, and resulting

in a voltage proportional to the oxygen concentration.

Typically the sensor is calibrated by adjusting for zero reading with nitrogen applied, and for

span using a cylinder containing 20.9% O

, though fresh air can be used for a quick check.

Both span and zero adjustments are made via front panel controls.

The sensor fitted has a long operational life and is very stable. If the output falls (i.e. the gas

reading is low), the sensor should be replaced. Sensor lifetime depends primarily conditions of

use (e.g. average sample oxygen concentration, sample flow rate, temperature), and so this

part is excluded from the instrument warranty. For typical applications, ADC recommends

routine replacement of the sensor every two years as part of the maintenance programme.

ADC (Sales & Service) Ltd. or their authorised local agents can supply replacement sensors with

the correct fittings and electrical characteristics. Fitting alternative parts may cause problems

and will invalidate the instrument warranty.

2. INSTALLATION

2.1 Installation Arrangement

The basic arrangement of the Instrument is a ‘3U’ high, 483mm (19”) chassis for rack

mounting, or alternatively, it may be supplied with a case for bench mounting.

All power input, output and gas connections are via the rear panel.

Power connection is via a standard three-way IEC power plug. A suitable plug and cable is

supplied.

Gas connection details are indicated in Section 2.7.

RS232C, analogue and alarm contact outputs are detailed in sections 2.4, 2.5 and 2.6

respectively.

2.2 Location & Ambient Conditions

The location must provide firm support and access to the rear of the instrument when the

instrument is mounted in the normal attitude on its base. When installed in a rack, the use of

runners is recommended.

It is not necessary to force ventilate the enclosure to cool the unit, but free circulation of air is

necessary for accuracy and reliability.

Although it is not necessary to maintain a controlled environment during use, a reasonably

stable ambient temperature gives best results. Sudden changes in temperature will disturb the

IRGA bench(s), causing a shift in readings until the compensation recovers. If a drop in

temperature is expected, it is best to leave the instrument energised (switched 'ON'), to avoid

possible condensation of water in the optical bench. If not being used in this condition, it is also

better to switch off the sample pump as this not only prolongs the life of the pump, but helps to

reduce condensation.

In all cases the ambient conditions must comply with the specifications. High

ambient conditions will affect reliability.

IMPORTANT: The MGA series analysers are not certified for operation in hazardous

environments.

2.3 Power Supply Setting & Connections

2.3.1 Power Supply Setting

The instrument operates from single phase, 110, 220 or 240 volts nominal AC, at 50 or 60 Hz.

The supply frequency is not critical, but the voltage must be set on the instrument to suit the

local power supply.

The voltage setting and connections are on the rear panel.

On delivery, the instrument is usually set for 240 volts operation. In this case, the number '240’

can be seen in the window of the voltage selector, just below the inlet socket.

If 220VAC or 110VAC operation is required, the voltage setting must be changed via the

combined voltage selector and fuse holder.

The selector is removed by pushing down the dip and pulling the fuse out. Pull the fuse holder

out and rotate it so that the voltage required shows in the selector window. If necessary,

change the fuse according to the table below.

Supply Fuse Ratings

110V 220V 240V

2A T 1A T 1A T

Spare fuses are provided which are 20 X 5 mm ceramic HRC ‘T’ (Time Delay) types.

Maximum Power consumption is 120VA.

2.3.2 Power Supply Connections

The power cable supplied must be connected to a suitable plug or distribution board

as follows:

BROWN - Line or High Voltage

BLUE

- Neutral or Low Voltage

GREEN/YELLOW - Earth or Ground

For safety reasons the Earth connection MUST provide a low resistance to Ground.

Further protection is provided by making a direct Earth-Bonded connection to the chassis of the

instrument, via a 4mm screw. This bonding is just below the voltage selector.

The instrument is provided with an ON/OFF switch under the power socket.

WARNING

• If the front, top or bottom sections of the enclosure are removed, BEWARE of

HIGH VOLTAGES near the power connector, switch and internal supply.

• When REMOVING or REPLACING the enclosure sections ALWAYS disconnect the

mains supply FIRST.

• Avoid touching the electronic boards. If these are removed for any reason -

SWITCH OFF the instrument FIRST.

• DO NOT HANDLE without ANTI-STATIC precautions being taken.

2.4 Serial I/O (RS232C)

An industry-standard serial port is fitted which allows the analyser to be connected to a wide

range of computer equipment for logging and remote control. The connector is similar to an

‘AT’ style PC serial port allowing the use of standard cables.

The serial port is configured from the front panel – see section 3.7.2. The serial port protocol is

detailed in section 3.7.1.

Serial (RS232C) Port Connections

Pin Name Function

1 - no connection

2 Rx Received data (input)

3 Tx Transmitted data (output)

4 DTR Handshake for Rx (output)

5 ground 0V (nominally chassis)

6 - no connection

7 RTS ‘true’ whenever unit is powered

8 CTS Handshake for Tx (input)

9 - no connection

Notes:

1. DTR is normally ‘true’

2. CTS is monitored only when ‘hardware handshake’ is selected

3. Screened cables must be used for RS232 connections

In common with all RS232C ports, long cable runs can cause problems with data corruption and

noise. Keep cables as short as practicable as – certainly no longer as 30 meters at 9600 baud.

Route signal cables well away from power cables, switchgear and other noise sources. For long

cable runs, and in electrically noisy environments, optical RS232C cable extenders are

recommended. Contact ADC (Spares & Service) Ltd. or their local authorised agents for advice.

2.5 Analogue Outputs

Analogue outputs are provided for connection to chart recorders, remote meters, analogue

logging equipment etc. Up to four outputs are available; one for each gas reading.

The outputs are arranged so that the reading shown at the top of the screen is presented on

analogue output 1, the reading on the next line down (if any) is presented on output 2 and so

on. Where there are fewer than four gas readings, unused analogue outputs will be inactive or

not fitted.

The analogue outputs are available via a circular ‘DIN’ connector on the rear panel, labelled

‘OUTPUTS’. A suitable connector is provided in the kit with each instrument, and further

supplies are available from ADC (Spares & Service) Ltd. or their authorised local agent.

+ -

Channel 1 3 8

Channel 2 7 5

Channel 3 2 4

Channel 4 6 1

NOTES:

1. V is used to indicate pin functions when output is set to voltage mode

2. I is used to indicate pin functions when output is set to 4..20mA mode

3. Screened cable should be used for analogue output connections (screen to connector shell).

Each output can be set to one of:

• 0 – 1V ]

• 0 – 5V ]- voltage modes

• 0 – 10V ]

• 4 – 20mA - current mode

Independently, using jumper links inside the case as shown in the section below.

2.5.1 Setting the analogue outputs

The procedure is as follows:

1. Disconnect the mains supply from the analyser, together with all the signal cables.

2. Isolate gas supplies, then remove the gas connections if necessary, taking all necessary

precautions.

3. Remove the top cover from the instrument by undoing the six screws on the top face, and

two screws on the back edge of the cover plate. Lift the cover clear.

4. Locate the RS232C connector on the rear panel, then look inside to locate the connector on

the circuit board (PC 392). The jumper links are all near to the RS232 connector, as shown

on the drawing (Fig. 3).

Voltage

+ -

Channel 1 3 8

Channel 2 7 5

Channel 3 2 4

Channel 4 6 1

Figure 2 – Analogue Output

pin numbers

5. In the drawing, the jumper settings

shown illustrate the different settings as

follows:

Output 1 – 10V

Output 2 – 5V

Output 3 – 4.. 20mA

Output 4 – 1V

6. Set the links as required, by pulling

them off the pins with tweezers or a

small pair of pliers, and then very

carefully re-seat them in the new

positions. The links should slide on

easily if they are aligned correctly.

7. Re-fit the top panel completely before

making connections and applying

power.

WARNING

Applying voltages to analogue outputs set to voltage mode will cause damage!

Check link settings before making connections

2.6 Alarm (Trip) Outputs

The alarm outputs are isolated relay contacts which can be set to operate at certain gas levels,

or on sample flow error. Up to five contacts may be available depending on the specification of

the instrument. The number actually available is shown on the trip set-up screen (see section

3.6.1).

Alarm contact outputs are available via a 14 way Amphenol connector on the rear panel. A

suitable connector is provided in the kit with each instrument, and further supplies are available

from ADC (Spares & Service) Ltd. or their authorised local agent.

The connector pin functions are printed on the rear panel adjacent

to the connector, and the pin numbering scheme is shown in Fig 4.

See section 7.3 for specifications.

A nominal 24 Volt (±20%) DC supply is available at the alarm

connector which can be used to power larger relays, sirens,

indicator lamps etc. This power source is internally fused at 1A

and the maximum continuous load is 500mA. The +24V DC

supply is referenced to chassis ground.

Figure 3 - Position of the Voltage/Current selection

links on the PCB

(rear panel view)

Figure 4 - Alarm

connector pin numbers

2.7 Gas Arrangements

2.7.1 The Gas Circuit

The gas connections within the instrument are shown on the gas circuit enclosed with this

manual. The gas circuit is quite specific to a particular instrument and shows how the gas is

routed from the inlets to individual analysis bench(s). Gas connections are via 'entries' that are

located on the rear panel.

All external connections are made with 6.35mm (1/4'') pipe fittings. The type of piping used is

recommended to be either polythene for general use or polytetraflurothalene (PTFE) or

stainless steel for corrosive gases.

All entries are fitted with in-line filters that are intended to stop any foreign matter entering the

instrument as a last resort. Unless the gas is perfectly clean and dry, particulate filters

and / or driers must be fitted externally. Contact ADC (Spares & Service) Ltd. or their

authorised local agents for advice.

The requirements for particular gases vary with the application and therefore these and the gas

circuit are specific to the delivered Instrument. Some guidelines follow, but it is the

responsibility of the installer to ensure that all safety and other requirements are met.

The Instrument Specification accompanying the Instrument defines the specific requirements

and this must be referred to during installation.

WARNING

• All Gases are potentially toxic and hazardous to health.

• All gas lines and connections must be leak-tight. Joints can be checked by

applying water containing some liquid soap and looking for bubbles.

• Exhaust lines must be properly vented and arranged to prevent blockage.

• Ventilate the enclosure to prevent a build-up of gas in the event of a leak.

2.7.2 The Sample Gas

The gas to be measured is the 'sample gas' labelled 'GAS IN'. After passing through the gas

circuit the measurement gases are exhausted at the entry labelled 'GAS OUT'. The analyser is

designed to receive sample gas at nominally atmospheric pressure, using the internal sample

pump to control the flow.

The Sample Gas supplied to the Instrument must be relatively clean, cool and of low moisture

content. Samples containing dust or particulates must be filtered externally and the filters

serviced at regular intervals.

Hot Samples with high moisture content should be passed through a water trap or dissector

after cooling.

To prevent the possibility of condensation in the Instrument if the Instrument is not in

continuous use, it is recommended that it is left Switched on with the Sample Pump Switched

off.

Samples may contain other gases which ‘interfere’ with the gas being measured. The extent to

which known interferents can affect the measurement are defined in the Instrument

Specification.

Sample gas pipes shall be inert to and shall not contaminate the gas.

The response time for a change in concentration will be affected by the sample flow rate.

Instrument response times are normally quoted for the recommended 500ml min

-1

flow rate,

ignoring the effect of sample pipe volume. Lower flow rates will increase the response time, as

will the volume of the sample piping. Higher flow rates will reduce the response time, but

excessive flow will pressurise the instrument which may cause damage or measurement errors.

If it is necessary to draw higher flows than recommended (e.g. due to long sample gas lines), it

will be necessary to provide some means of bypassing the excess flow to exhaust.

2.7.3 The Span Gas

The Span Gas is used for calibration and is a known concentration of the measured gas -

usually between 50% and 80% of the full-scale range of the Instrument. The gas is usually

obtained specially mixed in a pressurised cylinder and this must be fitted with a 2-stage

pressure regulator, with an output pressure indication of 0 - 0.3 Bar (0-5psig).

The Regulator should be set to give a nominal output pressure of 0.2 Bar (3psig). This will

usually give a suitable gas flow during a span operation (i.e. flow indicator approximately mid-

position). If necessary, a small adjustment to the pressure will provide correct flow.

WARNING – Application of gas pressures above 0.3 Bar / 5 psig will damage the

instrument.

2.7.4 The Zero Gas

The zero gas is used to check/set the reading from the optical benches in the zero

concentration condition. Dry nitrogen is the preferred zero gas as it is cheap and readily

available.

The zero gas must not contain any significant traces of the gas measured or interferents. For all

types of instruments and gases measured, nitrogen (from a cylinder) is usually specified. For

some gases however, fresh air may be used (for example on high concentration CO and CO

Instruments). When fresh air is used, it shall be drawn from 'outside’ air and away from any

possible contamination from such as Exhaust Ducts, Chimneys, etc.

In most respects fresh air should be treated in the same way as the sample gas with regard to

filtering, moisture content etc. See span gas, section 2.7.3.

2.7.5 The Exhaust Gas

Exhaust gas is the sample (or zero/span) gas that has passed through the analyser. For

hazardous gases (high concentrations, flammable or poisonous), exhaust gas must be carefully

routed to a safe venting point.

It is important to minimise ‘back pressure’ at the GAS OUT port, as this will affect readings and

reduce the efficiency of the sample pump. Where long runs of pipe are necessary, larger bore

pipe should be used via a suitable adapter. Where the exhaust pipe is connected to a forced air

extraction duct, make sure that any suction is minimal.

2.7.6 Gas Pump(s)

Gas pumps fitted in the instrument are of the vibrating diaphragm type and are capable of up

to 1.0 I/min

under pressures normally encountered.

The sample pump operates at fixed speed and at a flow rate of nominally 500 ml/m1n

. If it

should be necessary to adjust the flow, it can be set using the potentiometer VR2 on the power

supply board and / or the throttle (when fitted).

The internal sample pump is operated via the front panel 'PUMP' menu button.

Certain instrument configurations may be fitted with a second internal pump which is used to

circulate purge gas. This pump would be set to run continuously at a factory set rate.

2.8 Use of Chemicals (certain models only)

Certain instruments use chemicals to remove (or strip) certain gases from the air for zero

adjustment, or to purge the optics to prevent ambient air from affecting readings. These

chemicals must be replaced regularly to ensure efficient operation and hence good accuracy.

The chemicals are contained in glass ‘columns’ which are accessible from the front of the

instrument to aid inspection and refilling.

The chemicals that may be used are listed below under the gas application.

2.8.1 Water Vapour

An indicating form of calcium sulphate (CaSO

) known as 'DRIERITE' is normally supplied with

new instruments and replacement supplies are available from ADC (Spares & Service) Ltd or

their local authorised agents. In use, drierite changes from blue to pink as it becomes

exhausted, making it obvious when the container should be refilled with fresh chemical.

Drierite can be recovered by drying.

Magnesium Perchlorate (Mg (ClO

)

0 (also known as Anhydrone) is also suitable, but it is a

strong oxidising agent, which may restrict its use. It is an effective drier, but does not provide

any indication when it is exhausted and is difficult to recover. As more water vapour is

absorbed it takes on a solid appearance, at which time it should be replaced.

If water vapour is to be removed from gases external to the instrument, calcium chloride

(CaCl

) is an inexpensive and efficient chemical to use. When absorbing moisture however, it

forms a corrosive liquid and therefore the container should be made of glass, with a moisture

trap.

‘Silica gel’ is a good indicating drier, but can ‘hang on’ to some gases, especially C0

, giving

false readings, and is not generally recommended.

2.8.2 Carbon Dioxide

To remove C0

, usually in a C0

Instrument, indicating ‘soda lime’ is used. Soda lime consists

of about 80% calcium hydroxide ((Ca (0H)

)), 4% sodium hydroxide (NaOH) and 0.2%

indicator (green to brown).

In use, soda lime changes from green to brown and must be changed when green is no longer

visible. It is not recoverable. Replacement supplies are available from ADC (Spares & Service)

Ltd or their local authorised agents.

Other chemicals may produce corrosive by-products which can damage the instrument.

2.8.3 Precautions

Any chemical intended for use in the instrument is provided with it in a separate container,

labelled with international identification labels. Under normal use, the quantity supplied will last

for about 6 months to a year. Replacements can be obtained from ADC (Spares & Service)

Limited who will also advise on the use of chemicals obtainable by the User.

When handling chemicals, refer to the ‘Safety Letter’ enclosed in the manual for precautions

against possible health risk. For all chemicals, avoid skin and eye contact and do not taste or

swallow them.

As Magnesium Perchlorate is an oxidising agent, do not bring it into contact with

combustible material and dispose of it in a sealed glass container.

2.9 Pre-operation Checks

Before connection power to the instrument, check:

1. The voltage indicated on the voltage selector matches the local supply

2. That gas connections are leak free

3. That the exhaust gas venting arrangements are safe for the gases in the sample

4. That the instrument is properly grounded (earthed).

2.10 General Advice

2.10.1 Use of Gas Cylinders

Before use, Gas Cylinders must be checked to ensure that -

• the cylinders are securely located.

• the cylinders are fitted with a two-stage regulator.

• the cylinders contain the correct gas mixture for use.

• the cylinders are connected to the correct ‘entry’ on the Instrument.

• the cylinder's Output Pressure regulator is 'OFF'.

During use, check -

• the Instrument is 'ON'.

• the Sample Pump is 'ON'.

• the Output Pressure regulator is set for 0.2 Bar.

After use, check -

• the Output Pressure regulator is turned 'OFF'.

• the cylinder tap is turned 'OFF'.

• if the Instrument is in ‘Standby’, turn 'OFF' the Sample Pump.

Following a cylinder change, it is advisable to initiate a Span or Zero cycle a few minutes after

the supply is re-connected.

2.10.2 Gas Leaks

All external-piping connections must be checked for gas leaks, to ensure that no gases are

leaking to the local area (which may be a health hazard), and that no uncontrolled air or gas is

drawn into the Instrument (and so affect the measurement).

Applying water containing a mild soap solution can check connections under pressure. Do not

increase the pressure to check for leaks (or for any other reason), since this may damage the

Instrument.

Connections of pipes under nominally ambient pressure, such as the sample piping, are difficult

to check for leaks, but can be checked for tightness.

2.10.3 Exhausting & Ventilation

Because any gas is potentially toxic, and, some may be inflammable, the gas must be

exhausted to where it will be rapidly dispersed. For the same reasons, the Instrument and its

environment including the location of gas cylinders must be properly ventilated to minimise the

dangers of gas leaks.

If Span cylinders contain hazardous or inflammable gases, they must carry suitable warning

labels, and if inflammable, must be located in a suitable ‘Inflammable Store’ when in use or in

storage.

In all cases the local safety regulations must be consulted and followed.

3. SETTING UP

3.1 Preview

This section describes the settings available from the front panel. Factory settings have been

chosen to suit the general application of the instrument, or in accordance with the particular

instructions specified previously by the user.

3.2 On Power Up

IMPORTANT: Before operating the Instrument, ensure all the relevant installation

checks have been carried out [refer to Section 2.9], and that if a filter column is

fitted, it is properly charged with the chemical supplied.

Immediately after power is applied, the display presents a screen for 10 seconds. This page

contains the software version number.

If the logo does not appear on the screen within 20 seconds of applying power, try

adjusting the ‘LCD’ control, using a 2mm flat bladed screwdriver through the labelled

hole in the rear panel.

The next screen is the main display, which will show the measured value(s), units and the Gas

type, sample flow status and key functions.

The measured value is initially replaced with a symbol of a thermometer until the instrument

has warmed up.

Pressing the key labelled ‘Set Up’ displays a second screen showing the gas(s) measured

together with the range and units.

3.3 Zero & Span Operations.

Before precise gas readings can be obtained, the analyser must be adjusted so that it reads

zero when there is no trace of the measured gas present, then, when a known concentration of

the gas is applied, the reading is adjusted to agree with this concentration. These adjustments

are known as ‘zero’ and ‘span’ respectively.

The gases used for zero and span adjustment are supplied through the inlets at the back of the

instrument (see section 2.7), and electrically operated valves are used to route the appropriate

gas in place of the sample automatically when zero or span adjustment is selected using the

front panel controls.

'How often' to Zero or Span varies with each instrument. The interval required depends on how

much re-adjustment is being carried out: this can be established by noting the discrepancy of

the displayed value prior to resetting.

If the discrepancy is less than 0.5% of full scale, the intervals can be increased, or if this is not

accurate enough, decreased. Generally Zeroing is required more often than Spanning, so that

typically a daily Zero, with weekly Span is adequate.

The instrument can be set to automatically adjust zero on a periodic basis. The period can be

set from 1 hour to 250 hours.

See section 4 for details.

3.4 Display & Keypad

3.4.1 Display

The normal operating layout is shown in Fig 5,

but note that this is an example; the gases

shown will vary with the specification ordered.

On the left of the screen are the gas names,

followed by the current reading(s). A

thermometer symbol indicates that the

analysis bench is warming up – readings will

be shown when warm-up is completed.

On the right, adjacent to the five ‘function’

keys, are the key labels. These describe the functions of the keys at any time, and the labels

change as different options are selected.

Between the gas readings and the function key labels, is the sample flow indicator, which is

designed to mimic a float flowmeter. Normally, the flow, as indicated by the ‘float’, should be

around the centre of the indicator. If the float is in a shaded region, the flow is too high or low

and a warning triangle is shown.

Flow fail and alarm trips are indicate at the bottom of the display.

The LCD display is affected by ambient

temperature and viewing angle. A contrast

control is provided to adjust the display to

give the best contrast under all viewing

conditions.

To adjust the contrast, Select the following

menu functions:

Set Up , Display

The contrast screen is displayed. Use the

lighter and darker controls to get the best

display. The bar shows the amount of

Figure 6 - screen contrast adjustment

Figure 5 - Example Main Screen (3 gas + ratio

model)

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ADC MGA3000 series Operating instructions

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