Teledyne 3000TA-XL-EU User Manual

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Trace Oxygen Analyzer

OPERATING INSTRUCTIONS FOR

Model 3000TA-XL-EU

Trace Oxygen Analyzer

DANGER

HIGHLY TOXIC AND OR FLAMMABLE LIQUIDS OR GASES MAY BE PRESENT IN THIS MONITORING SYSTEM.

PERSONAL PROTECTIVE EQUIPMENT MAY BE REQUIRED WHEN SERVICING THIS SYSTEM.

HAZARDOUS VOLTAGES EXIST ON CERTAIN COMPONENTS INTERNALLY WHICH MAY PERSIST FOR A TIME EVEN AFTER THE POWER IS TURNED OFF AND DISCONNECTED.

ONLY AUTHORIZED PERSONNEL SHOULD CONDUCT MAINTENANCE AND/OR SERVICING. BEFORE CONDUCTING ANY MAINTENANCE OR SERVICING CONSULT WITH AUTHORIZED SUPERVISOR/ MANAGER.

P/N M69603 11/24/04 ECO # 03-0126

Teledyne Analytical Instruments

Model 3000TA-XL-EU

All Rights Reserved. No part of this manual may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any other language or computer language in whole or in part, in any form or by any means, whether it be electronic, mechanical, magnetic, optical, manual, or otherwise, without the prior written consent of Teledyne Analytical Instruments, 16830 Chestnut Street, City of Industry, CA 91749-1580.

Warranty

This equipment is sold subject to the mutual agreement that it is warranted by us free from defects of material and of construction, and that our liability shall be limited to replacing or repairing at our factory (without charge, except for transportation), or at customer plant at our option, any material or construction in which defects become apparent within one year from the date of shipment, except in cases where quotations or acknowledgements provide for a shorter period. Components manufactured by others bear the warranty of their manufacturer. This warranty does not cover defects caused by wear, accident, misuse, neglect or repairs other than those performed by Teledyne or an authorized service center. We assume no liability for direct or indirect damages of any kind and the purchaser by the acceptance of the equipment will assume all liability for any damage which may result from its use or misuse.

We reserve the right to employ any suitable material in the manufacture of our apparatus, and to make any alterations in the dimensions, shape or weight of any parts, in so far as such alterations do not adversely affect our warranty.

Important Notice

This instrument provides measurement readings to its user, and serves as a tool by which valuable data can be gathered. The information provided by the instrument may assist the user in eliminating potential hazards caused by his process; however, it is essential that all personnel involved in the use of the instrument or its interface, with the process being measured, be properly trained in the process itself, as well as all instrumentation related to it.

The safety of personnel is ultimately the responsibility of those who control process conditions. While this instrument may be able to provide early warning of imminent danger, it has no control over process conditions, and it can be misused. In particular, any alarm or control systems installed must be tested and understood, both as to how they operate and as to how they can be defeated. Any safeguards required such as locks, labels, or redundancy, must be provided by the user or specifically requested of Teledyne at the time the order is placed.

Therefore, the purchaser must be aware of the hazardous process conditions. The purchaser is responsible for the training of personnel, for providing hazard warning methods and instrumentation per the appropriate standards, and for ensuring that hazard warning devices and instrumentation are maintained and operated properly.

Teledyne Analytical Instruments, the manufacturer of this instrument, cannot accept responsibility for conditions beyond its knowledge and control. No statement expressed or implied by this document or any information disseminated by the manufacturer or its agents, is to be construed as a warranty of adequate safety control under the

user’s process conditions.

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Trace Oxygen Analyzer

Specific Model Information

Theinstrumentforwhichthismanualwassuppliedmayincorporateoneor moreoptionsnotsuppliedinthestandardinstrument.Commonlyavailable options are listed below, with check boxes. Any that are incorporated in the instrumentforwhichthismanualissuppliedareindicatedbyacheckmarkinthe box.

Instrument Serial Number: _______________________

OptionsIncludedintheInstrumentwiththeAboveSerialNumber:

3000TA-XL-VS: 3000TA-XL-CV: 19" Rack Mnt:

InstrumentconfiguredforVacuumService

Instrumentwithcalibrationvalves

The19"RelayRackMountunitsareavailablewith eitheroneortwo3000TA-XLseriesanalyzersinstalled in a standard 19" panel and ready to mount in a standard rack.

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Model 3000TA-XL-EU complies with all of the requirements of the Commonwealth of Europe (CE) for Radio Frequency Interference, Electromagnetic Interference (RFI/EMI), and Low Voltage Directive (LVD).

The following International Symbols are used throughout the Instruction Manual for your visual and immediate warnings and when you have to attend CAUTION while operating the instrument:

STAND-BY, Instrument is on Stand-by, but circuit is active

GROUND

Protective Earth

CAUTION, The operator needs to refer to the manual for further information. Failure to do so may compromise the safe operation of the equipment.

CAUTION, Risk of Electric Shock

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Trace Oxygen Analyzer



		Table of Contents

1 Introduction
1.1	Overview ........................................................................		1-1
1.2	Typical Applications .......................................................		1-1
1.3	Main Features of the Analyzer .......................................		1-1
1.4	Model Designations .......................................................		1-2
1.5	Front Panel (Operator Interface) .....................................		1-3
1.6	Rear Panel (Equipment Interface) ..................................		1-5

2 Operational Theory
2.1	Introduction ....................................................................	2-1
2.2	Micro-Fuel Cell Sensor ..................................................	2-1

	2.2.1		Principles of Operation ............................................	2-1
	2.2.2 Anatomy of a Micro-Fuel Cell ..................................			2-2
	2.2.3		Electrochemical Reactions ......................................	2-3
	2.2.4 The Effect of Pressure..............................................			2-4
	2.2.5		Calibration Characteristics ......................................	2-4
	2.3	Sample System ..............................................................		2-5
	2.4	Electronics and Signal Processing ................................		2-8
3	Installation
	3.1	Unpacking the Analyzer .................................................		3-1
	3.2	Mounting the Analyzer ...................................................		3-1
	3.3	Rear Panel Connections ................................................		3-2
	3.3.1		Gas Connections ...................................................	3-3
	3.3.2		Electrical Connections ...........................................	3-4
		3.3.2.1 Primary Input Power.......................................		3-4
		3.3.2.2 50-Pin Equipment Interface Connector ..........		3-4
		3.3.2.3 RS-232 Port ...................................................		3-9
	3.4	Installing the Micro-Fuel Cell .........................................		3-11
	3.5	Testing the System .........................................................		3-11
4	Operation
	4.1	Introduction ....................................................................		4-1
	4.2	Using the Data Entry and Function Buttons ...................		4-2
	4.3	The System Function .....................................................		4-3
	4.3.1 Tracking the O2 Readings during CAl & Alarm .......			4-4
	4.3.2 Setting up an Auto-Cal ...........................................			4-5
	4.3.3		Password Protection ..............................................	4-6
		4.3.3.1 Entering the Password ...................................		4-7

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	.............4.3.3.2 Installing or Changing the Password			4-8
4.3.4		Logout ....................................................................		4-9
4.3.5		System Self-Diagnostic Test ..................................		4-9
4.3.6		Version Screen ......................................................		4-10
4.4	Calibration of the Analyzer .............................................			4-11
4.4.1		Zero Cal .................................................................		4-11
	4.4.1.1		Auto Mode Zeroing ........................................	4-12
	4.4.1.2		Manual Mode Zeroing ....................................	4-12
	4.4.1.3		Cell Failure ....................................................	4-13
4.4.2		Span Cal ................................................................		4-14
	4.4.2.1		Auto Mode Spanning .....................................	4-14
	4.4.2.2		Manual Mode Spanning .................................	4-15
4.4.3		Span Failure ..........................................................		4-16
4.5	Switching of Sample Streams ........................................			4-16
4.5.1 Special notes on hydrogen gas stream ..................				4-17
4.6	The Alarms Function......................................................			4-17
4.7	The Range Function ......................................................			4-19
4.7.1 Setting the Analog Output Ranges.........................				4-20
4.7.2		Fixed Range Analysis............................................		4-20
4.8	The Analyze Function ....................................................			4-21
4.9	Signal Output .................................................................			4-21
Maintenance
5.1	Routine Maintenance .....................................................			5-1
5.2	Cell Replacement ..........................................................			5-1
5.2.1		Storing and Handling Replacement Cells ...............		5-1
5.2.2 When to Replace a Cell ...........................................				5-2
5.2.3		Removing the Micro-Fuel Cell .................................		5-2
5.2.4		Installing a New Micro-Fuel Cell ..............................		5-4
5.2.5 Cell Warranty ...........................................................				5-4
5.3	Fuse Replacement.........................................................			5-5
5.4	System Self Diagnostic Test ...........................................			5-5
5.5	Major Internal Components ............................................			5-6
5.6	Cleaning		........................................................................	5-7
5.7	Troubleshooting .............................................................			5-8
Appendix
A-1	Model 3000TA ...................................-XL Specifications			A-1
A-2	Recommended .........................2-Year Spare Parts List			A-3
A-3	Drawing List ...................................................................			A-4
A-4	19-Inch Relay ...................................Rack Panel Mount			A-4
A-5 Application .....................Notes on Pressures and Flow				A-5

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Appendix
A-6	Material Safety Data Sheet..................................................	A-8
A-7	Installing and Replacing Micro Fuel Cell.........................	A-12

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DANGER

COMBUSTIBLE GAS USAGE WARNING

This is a general purpose instrument designed for use in a nonhazardous area. It is the customer's responsibility to ensure safety especially when combustible gases are being analyzed since the potential of gas leaks always exist.

The customer should ensure that the principles of operation of this equipment is well understood by the user. Misuse of this product in any manner, tampering with its components, or unauthorized substitution of any component may adversely affect the safety of this instrument.

Since the use of this instrument is beyond the control of Teledyne, no responsibility by Teledyne, its affiliates, and agents for damage or injury from misuse or neglect of this equipment is implied or assumed.

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Trace Oxygen Analyzer		Introduction 1

Introduction

1.1Overview

The Teledyne Analytical Instruments Model 3000TA-XL Trace Oxygen Analyzer is a versatile microprocessor-based instrument for detecting oxygen at the parts-per-million (ppm) level in a variety of gases. This manual covers the Model 3000TA-XL General Purpose flush-panel and/or rackmount units only. These units are for indoor use in a nonhazardous environment.

1.2Typical Applications

A few typical applications of the Model 3000TA-XL are:

•Monitoring inert gas blanketing

•Air separation and liquefaction

•Chemical reaction monitoring

•Semiconductormanufacturing

•Petrochemical process control

•Quality assurance

•Gas analysis certification.

1.3Main Features of the Analyzer

The Model 3000TA-XL Trace Oxygen Analyzer is sophisticated yet simple to use. The main features of the analyzer include:

•A 2-line alphanumeric vacuum fluorescent display (VFD) screen, driven by microprocessor electronics, that continuously prompts and informs the operator.

•High resolution, accurate readings of oxygen content from low ppm levels through 25%. Large, bright, meter readout.

•Stainless steel cell block.

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•Advanced Micro-Fuel Cell, designed for trace analysis, has a 0-1 ppm low range with less than a 0.2 ppm offset and six months warranty and an expected lifetime of one year.

•Versatile analysis over a wide range of applications.

•Microprocessor based electronics: 8-bit CMOS microprocessor with 32 kB RAM and 128 kB ROM.

•Three user definable output ranges (from 0-1 ppm through 0- 250,000 ppm) allow best match to users process and equipment.

•Air-calibration range for spanning at 20.9 % (209,000 ppm) available.

•Auto Ranging allows analyzer to automatically select the proper preset range for a given measurement. Manual override allows the user to lock onto a specific range of interest.

•Two adjustable concentration alarms and a system failure alarm.

•Extensive self-diagnostic testing, at startup and on demand, with continuous power-supply monitoring.

•Two way RFI protection.

•RS-232 serial digital port for use with a computer or other digital communication device.

•Four analog outputs: two for measurement (0–1 V dc and Isolated 4–20 mA dc) and two for range identification.

•Convenient and versatile, steel, flush-panel or rack-mountable case with slide-out electronics drawer.

1.4Model Designations

3000TA-XL: Standard model for sample under pressure 3000TA-XL-VS: Instrument configured for Vacuum Service 3000TA-XL-CV: Instrument with calibration valves

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Trace Oxygen Analyzer		Introduction 1

1.5Front Panel (Operator Interface)

The standard 3000TA-XL is housed in a rugged metal case with all controls and displays accessible from the front panel. See Figure 1-1. The front panel has thirteen buttons for operating the analyzer, a digital meter, an alphanumeric display, and a window for viewing the sample flowmeter.

Function Keys: Six touch-sensitive membrane switches are used to change the specific function performed by the analyzer:

Door Latch

Digital Meter

Alphanumeric

Display

Sample System

FlowIndicator

Standby Switch

Data Entry Buttons	Function Buttons

Figure 1-1: Model 3000TA-XL Front Panel

•Analyze Perform analysis for oxygen content of a sample gas.

•System Perform system-related tasks (described in detail in

chapter 4, Operation.).

•Span Span calibrate the analyzer.

•Zero Zero calibrate the analyzer.

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•Alarms Set the alarm setpoints and attributes.

•Range Set up the 3 user definable ranges for the instrument.

Data Entry Keys: Six touch-sensitive membrane switches are used to input data to the instrument via the alphanumeric VFD display:

•Left & Right Arrows Select between functions currently

displayed on the VFD screen.

•Up & Down Arrows Increment or decrement values of

functions currently displayed.

•Enter Moves VFD display on to the next screen in a series. If

none remains, returns to the Analyze screen.

•Escape Moves VFD display back to the previous screen in a

series. If none remains, returns to the Analyze screen.

Digital Meter Display: The meter display is a Light Emitting Diode (LED) device that produces large, bright, 7-segment numbers that are legible in any lighting. It produces a continuous readout from 0-10,000 ppm and then switches to a continuous percent readout from 1-25%. It is accurate across all analysis ranges without the discontinuity inherent in analog range switching.

Alphanumeric Interface Screen: The VFD screen is an easy-to-use interface from operator to analyzer. It displays values, options, and messages that give the operator immediate feedback.

NeedleValve: To adjust flow of gas sample

Flowmeter: Monitors the flow of gas past the sensor. Readout is 0.2 to 2.4 standard liters per minute (SLPM) of nitrogen

Standby Button: The Standby turns off the display and outputs, but circuitry is still operating.

CAUTION: The power cable must be unplugged to fully disconnect power from the instrument. When chassis is exposed or when access door is open and power cable is connected, use extra care to avoid contact with live electrical circuits .

Access Door: For access to the Micro-Fuel Cell, the front panel swings open when the latch in the upper right corner of the panel is pressed

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Trace Oxygen Analyzer		Introduction 1

all the way in with a narrow gauge tool. Accessing the main circuit board requires unfastening rear panel screws and sliding the unit out of the case.

1.6Rear Panel (Equipment Interface)

The rear panel, shown in Figure 1-2, contains the gas and electrical connectors for external inlets and outlets. Some of those depicted are optional and may not appear on your instrument. The connectors are described briefly here and in detail in chapter 3 Installation.

Figure 1-2: Model 3000TA-XL Rear Panel

•Power Connection Universal AC power source.

•Gas Inlet and Outlet One inlet and one exhaust out.

• Analog Outputs	0–1 V dc oxygen concentration plus 0-1
	V dc range ID, and isolated 4–20 mA dc
	oxygen concentration plus 4-20 mA dc
	range ID.

•Alarm Connections 2 concentration alarms and 1 system

alarm.

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•	RS-232 Port	Serial digital concentration signal output
		and control input.
•	Remote Probe	Used in the 3000TA-XL for controlling
		external solenoid valves only.
•	Remote Span/Zero	Digital inputs allow external control of
		analyzer calibration.
•	Calibration Contact	To notify external equipment that
		instrument is being calibrated and
		readings are not monitoring sample.

•Range ID Contacts Four separate, dedicated, range relay

	contacts. Low, Medium, High, Cal.
• Network I/O	Serial digital communications for local
	network access. For future expansion.
	Not implemented at this printing.

Note: If you require highly accurate Auto-Cal timing, use external Auto-Cal control where possible. The internal clock in the Model 3000TA-XL is accurate to 2-3 %. Accordingly, internally scheduled calibrations can vary 2-3 % per day.

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Trace Oxygen Analyzer		Operational Theory 2

Operational Theory

2.1Introduction

The analyzer is composed of three subsystems:

1.Micro-Fuel Cell Sensor

2.Sample System

3.Electronic Signal Processing, Display and Control

The sample system is designed to accept the sample gas and transport it through the analyzer without contaminating or altering the sample prior to analysis. The Micro-Fuel Cell is an electrochemical galvanic device that translates the amount of oxygen present in the sample into an electrical current. The electronic signal processing, display and control subsystem simplifies operation of the analyzer and accurately processes the sampled data. The microprocessor controls all signal processing, input/output and display functions for the analyzer.

2.2Micro-Fuel Cell Sensor

2.2.1 Principles of Operation

The oxygen sensor used in the Model 3000TA-XL series is a MicroFuel Cell, Model B-2CXL designed and manufactured by Analytical Instruments. It is a sealed plastic disposable electrochemical transducer.

The active components of the Micro-Fuel Cell are a cathode, an anode, and the aqueous KOH electrolyte in which they are immersed. The cell converts the energy from a chemical reaction into an electrical current in an external electrical circuit. Its action is similar to that of a battery.

There is, however, an important difference in the operation of a battery as compared to the Micro-Fuel Cell: In the battery, all reactants are stored within the cell, whereas in the Micro-Fuel Cell, one of the reactants (oxygen)

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comes from outside the device as a constituent of the sample gas being analyzed. The Micro-Fuel Cell is therefore a hybrid between a battery and a true fuel cell. (All of the reactants are stored externally in a true fuel cell.)

2.2.2 Anatomy of a Micro-Fuel Cell

The Micro-Fuel Cell is a cylinder only 1¼ inches in diameter and 1¼ inches thick. It is made of an extremely inert plastic, which can be placed confidently in practically any environment or sample stream. It is effectively sealed, although one end is permeable to oxygen in the sample gas. The other end of the cell is a contact plate consisting of two concentric foil rings. The rings mate with spring-loaded contacts in the sensor block assembly and provide the electrical connection to the rest of the analyzer. Figure 2-1 illustrates the external features.

Figure 2-1: Micro-Fuel Cell

Refer to Figure 2-2, Cross Section of a Micro-Fuel Cell, which illustrates the following internal description.

Figure 2-2. Cross Section of a Micro-Fuel Cell (not to scale)

At the top end of the cell is a diffusion membrane of Teflon, whose thickness is very accurately controlled. Beneath the diffusion membrane lies

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Trace Oxygen Analyzer		Operational Theory 2

the oxygen sensing element—the cathode—with a surface area almost 4 cm2. The cathode has many perforations to ensure sufficient wetting of the upper surface with electrolyte, and it is plated with an inert metal.

The anode structure is below the cathode. It is made of lead and has a proprietary design which is meant to maximize the amount of metal available for chemical reaction.

At the rear of the cell, just below the anode structure, is a flexible membrane designed to accommodate the internal volume changes that occur throughout the life of the cell. This flexibility assures that the sensing membrane remains in its proper position, keeping the electrical output constant.

The entire space between the diffusion membrane, above the cathode, and the flexible rear membrane, beneath the anode, is filled with electrolyte. Cathode and anode are submerged in this common pool. They each have a conductor connecting them to one of the external contact rings on the contact plate, which is on the bottom of the cell.

2.2.3 Electrochemical Reactions

The sample gas diffuses through the Teflon membrane. Any oxygen in the sample gas is reduced on the surface of the cathode by the following HALF REACTION:

O2 + 2H2O + 4e– → 4OH–

(cathode)

(Four electrons combine with one oxygen molecule—in the presence of water from the electrolyte—to produce four hydroxyl ions.)

When the oxygen is reduced at the cathode, lead is simultaneously oxidized at the anode by the following HALF REACTION:

Pb + 2OH– → Pb+2 + H2O + 2e–

(anode)

(Two electrons are transferred for each atom of lead that is oxidized. Therefore it takes two of the above anode reactions to balance one cathode reaction and transfer four electrons.)

The electrons released at the surface of the anode flow to the cathode surface when an external electrical path is provided. The current is proportional to the amount of oxygen reaching the cathode. It is measured and used to determine the oxygen concentration in the gas mixture.

The overall reaction for the fuel cell is the SUM of the half reactions above, or:

2Pb + O2 → 2PbO

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(These reactions are specific to oxygen as long as no gaseous components capable of oxidizing lead—such as iodine, bromine, chlorine and fluorine—are present in the sample.)

In the absence of oxygen, no current is generated.

2.2.4 The Effect of Pressure

In order to state the amount of oxygen present in the sample in parts- per-million or a percentage of the gas mixture, it is necessary that the sample diffuse into the cell under constant pressure.

If the total pressure increases, the rate that oxygen reaches the cathode through the diffusing membrane will also increase. The electron transfer, and therefore the external current, will increase, even though the oxygen concentration of the sample has not changed. It is therefore important that the sample pressure at the fuel cell (usually vent pressure) remain relatively constant between calibrations.

2.2.5 Calibration Characteristics

Given that the total pressure of the sample gas on the surface of the Micro-Fuel Cell input is constant, a convenient characteristic of the cell is that the current produced in an external circuit is directly proportional to the rate at which oxygen molecules reach the cathode, and this rate is directly proportional to the concentration of oxygen in the gaseous mixture. In other words it has a linear characteristic curve, as shown in Figure 2-3. Measuring circuits do not have to compensate for nonlinearities.

In addition, since there is zero output in the absence of oxygen, the characteristic curve has close to an absolute zero (less than ± 0.2 ppm oxygen). Depending upon the application, zeroing may still be used to compensate for the combined zero offsets of the cell and the electronics.

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Trace Oxygen Analyzer							Operational Theory 2

Figure 2-3. Characteristic Input/Output Curve for a Micro-Fuel Cell

2.3Sample System

The sample system delivers gases to the Micro-Fuel Cell sensor from the analyzer rear panel inlet. Depending on the mode of operation either sample or calibration gas is delivered.

The Model 3000TA-XL sample system is designed and fabricated to ensure that the oxygen concentration of the gas is not altered as it travels through the sample system.

The sample system for the standard instrument incorporates VCR tube fittings for sample inlet and 1/4"outlet tube connections at the rear panel. The sample or calibration gas that flows through the system is monitored by a flowmeter downstream from the cell. Figure 2-4 shows the piping layout and flow diagram for the standard model.

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2 Operational Theory		Model 3000TA-XL-EU

SAMPLEIN EXHAUST

TOP	RIGHT SIDE
VCR	Exhaust
Sample In	Out

Cell

Block

NeedleValve

Flowmeter

Figure 2-4: Piping Layout

Figure 2-5 is the flow diagram for the sampling system. In the standard instrument, calibration gases can be connected directly to the Sample In port by teeing to the port with appropriate valves.

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Trace Oxygen Analyzer		Operational Theory 2

Figure 2-5: Flow Diagram-Sample Under Pressure

-Standard Model

-Do not exceed 10" Hg Vacuum-

Figure 2-5-1: Flow Diagram-Sample at Zero Pressure

-Model 3000TA-XL-VS

Figure 2-5-2: Flow Diagram-Sample Under Pressure

-Model 3000TA-XL-CV

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2.4Electronics and Signal Processing

The Model 3000TA-XL Trace Oxygen Analyzer uses an 8031 microcontroller with 32 kB of RAM and 128 kB of ROM to control all signal processing, input/output, and display functions for the analyzer. System power is supplied from a universal power supply module designed to be compatible with any international power source. Figure 2-6 shows the location of the power supply and the main electronic PC boards.

The signal processing electronics including the microprocessor, analog to digital, and digital to analog converters are located on the motherboard at the bottom of the case. The preamplifier board is mounted on top of the motherboard as shown in the figure. These boards are accessible after removing the back panel. Figure 2-7 is a block diagram of the Analyzer electronics.

Figure 2-6: Electronic Component Location Inside the Model 3000TA-XL

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Trace Oxygen Analyzer

Operational Theory 2

Figure 2-7: Block Diagram of the Model 3000TA-XL Electronics

In the presence of oxygen the cell generates a current. A current to voltage amplifier converts this current to a voltage, which is amplified in the second stage amplifier.

The second stage amplifier also supplies temperature compensation for the oxygen sensor output. This amplifier circuit incorporates a thermistor,

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which is physically located in the cell block. The thermistor is a temperature dependent resistor that changes the gain of the amplifier in proportion to the temperature changes in the block. This change is inversely proportional to the change in the cell output. The result is a signal that is temperature independent within a specified tolerance. The output from the second stage amplifier is sent to an 18 bit analog to digital converter controlled by the microprocessor.

The digital concentration signal along with input from the control panel is processed by the microprocessor, and appropriate control signals are directed to the display, alarms and communications port. The same digital information is also sent to a 12 bit digital to analog converter that produces the 4-20 mA dc and the 0-1 V dc analog concentration signal outputs, and the analog range ID outputs.

Signals from the power supply are also monitored, and through the microprocessor, the system failure alarm is activated if a malfunction is detected.

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