Emerson 2468CB, 2468CD User Manual

Operating Manual

24685034, Rev. AE June 2011

Hydrastep 2468

Hydrastep 2468CB and 2468CD

Electronic Gauging System

(Dual Power Supply Version)

www.mobrey.com

 Refer to Part 1, Section 2.4.2.4.

 Wrong voltage setting.

 Incorrect supply.

 Blown fuse.

 Incorrect cable termination.  Incorrect supply.

 Refer to Part 1, Section 2.4.2.4.

 Blown fuse.

 Incorrect cable termination.

 Refer to Part 1, Section 2.5.2.1.

 Refer to Part 1, Section 2.5.2.2.

 Check Main Display, as above.

 See Part 1, Section 4.2 (Relevant display).

 Check cable connections. See Part 1, Section4.4.

 Refer to Part 2, Section 3.

 Refer to Part 2, Section 2.3.

 Incorrect configuration.  Refer to Part 1, Section 2.5.2.

 Incorrect configuration.

 Incorrect interface cable connection.

 Electrode contamination  Incorrect column installation reducing

 Refer to Part 1, Section 2.5.1.3.

 Refer to Part 1, Section 2.5.1.4.

 Refer to Part 1, Section 2.5.2.3.  Refer to Part 2, Section 3.

condensate flow.

 Water conductivity is too high.

 Threshold not matched to application.

 Electrode contamination.

CATEGORY SYMPTOM POSSIBLE CAUSES (See Note 1) SOLUTION (See Note 2)

 Hydrastep system does not power-up.

PSU (AC)

LED’s with Yellow alarm LED illuminated.

 Hydrastep system does not power-up.

PSU (DC)

 Chequered / intermittent display.

 No display.

 Yellow LED illuminated.

 Chequered / intermittent display.

MAIN DISPLAY

REMOTE DISPLAY

 No display.

 Yellow LED illuminated.

 Flashing Red (steam) and Green (water)

ERROR

ELECTRODE ALARM

yellow LED illuminated

 Water above steam (green above red) with

SWITCHING

THRESHOLD

WATER/STEAM

Note 1: Further detailed information can be found in Fault finding Part 1, Sections 2.6 and 4.5.

Note 2: References are to Operating Manuals 24685033 (for 2468CA and 2468CC models) and 24685034 (for 2468CB and 2468CD models).

condensate flow back into the column.

HYDRASTEP START-UP

It is possible that some of these conditions will be seen on a new Hydrastep installation.

** This does not mean that the equipment you have purchased is faul ty ** Due to the nature of the areas that Hydrastep is normally installed, various conditions can occur that make the instrument operate in an unusual manner.

It would be easy to think you have installed defective equipment, but it is very unlikely that this is the case.

Great care must be taken when installing a Hydrastep system so that these problems are less likely to be seen; firstly, please take th e time to ensure that the various people involved

in the fitting of the components have been shown and have read the handbook, which is supplied with all new Hydrastep systems.

This, along with the wiring diagrams (also supplied), should make for a trouble free installation. 1. Please read and understand Part 2 of the handbook, which explains the pressure sid e of the equ ipment.

2. Ensure wiring is of the correct type and that the wiring diagram supplied has been followed.

3. Hydrastep relies on a ‘path back to earth’. Please make sure that all earth points are made and are of a good standard.

4. Great care must be taken with the mounting of the water column; the columns must be vertical; angles stated in the manual should be as close as possible, as this ensures

5. Lagging of the pipe work must be as stated; ** The last 0.5 m of the (top) steam leg MUST NOT be insulated as this will inhibit condensate flow into the column; this will cause a

picked up on the electrodes and shows its self as a flickering in the bottom few electrodes. When the system is brought up to its normal working condition’s this will settle but

can take a couple of days to do so.

flickering display.**

water conductivity is high. We can modify the units up to 1600Us/cm.

include mains voltage to be used, trip points (if relay cards are to be fitted), number of electrodes to be used and remot e display option (if ordered). These points are not pre-set

as standard as the factory do not know your requirement unless stated on your order.

process and a new set should go in before you run the system up for the first time.

not a fault and is caused by a few conditions specific to power stations:

(a) If a boiler is new or has seen a large amount re-work, it may well get a coating of magnetite inside of it, when it is first started up. This creates a small DC voltage that is

6. Please be aware of your water quality as some adjustments to the Hydrastep may be required if it has a high conductivity. Please let us know when placing your order if your

7. Units will not leave the factory configured for customer orders unless requested. If you wish it to be configured, please request it on your order and it will then be done. Options

8. Care should be taken to make sure that a new set of electrodes have been fitted after the first acid wash of the system. The electrodes may well have been damaged during this

9. The most common problem seen with Hydrastep systems is a flickering pattern on the display while the boiler is being brought up to operating pressure and temperature. This is

) Should the plant generate a higher than normal amount of DC noise, we can supply a blocking cap that is built into a PCB that will stop this problem.

(b) It is possible that the top electrodes may have a wet coating on them until these working conditions are met; again, if left to settle, this will work at normal working conditions.

If you are in any doubt about what you are doing, contact Customer Support of Mobrey Limited on +44 (0) 1753 756600 for guidance

Mobrey Customer Support

(April 2005)

About this manual

This manual describes the Hydrastep 2468CB and 2468CD Electronic Gauging Systems along with the recommended options. Except where stated otherwise, the information contained in this m anual can be assumed to apply to either system.

This manual is divided into three parts; the first covers the electrical/electronic system; the second describes the pressure parts; the third is for coverage of all other aspects.

Part 1 – Electrical/Electronic System

Chapter 1 introduces the Hydrastep 2468 Electronic Gauging System and its operating principles. Chapter 2 covers the installation, configuration and fault analysis procedures. Chapter 3 covers the installation, configuration and fault analysis procedures for the Relay Output Board (Chapter 3a),

the Delay Relay Output Board (Chapter 3b) and the Opto-isolated Output Board (Chapter 3c). Chapter 4 covers the installation, configuration and fault analysis procedures for all versi ons of the Remote

Display Unit.

Part 2 – Pressure Parts

Chapter 1 is a general introduction to the Hydrastep system of water level determination. Chapter 2 describes the water column and its components – the preparation, installation o f the water column on to

the boiler, acid and steam purging of the boiler system and the fitting of the electrode sensors. Chapter 3 details the fault repair procedures carried out on the system pressure parts and their commissioning. Chapter 4 provides a general description of the pressure parts used in the Hydrastep systems. Chapter 5 details the Pressure Parts specifications.

Caution:

For installation under the Pressure Equipment Directive (PED) 97/23/EC, refer to safety instruction manual 24688006/SI.

Caution:

For installation under ATEX directive 94/09/EC, refer to safety instruction manual 24685033/SI.

Part 3 – Appendix

Appendix A contains a CSA certified connection drawing and associated notes.

Caution:

For installation in potentially explosive atmospheres in Canada and USA, refer to control drawing 24685037 in Part 3.

SYMBOLS USED IN THIS MANUAL AND ON THE UNIT

Symbol Meaning

Direct Current

Alternating Current

Earth (ground) terminal

Protective conductor terminal

Caution (refer to accompanying documents)

Part 1

Hydrastep 2468CB & 2468CD

Electronic Gauging System

24685034 Pt.1-1

Pt.1-2 24685034

DANGEROUS VOLTAGES ARE PRESENT IN THIS EQUIPMENT. ANY WARNING NOTICES OR PROCEDURES CONTAINED IN THIS MANUAL OR ON THE EQUIPMENT SHOULD BE STRICTLY OBSERVED TO MAINTAIN SAFETY. THE USE OF THIS EQUIPMENT IN A MANNER NOT SPECIFIED IN THIS MANUAL MAY IMPAIR THE PROTECTION PROVIDED BY THIS EQUIPMENT. GREAT CARE SHOULD BE EXERCISED WHEN SERVICING THIS EQUIPMENT.

TO ENSURE COMPLIANCE WITH THE EMC DIRECTIVE (WHERE APPLICABLE) THE INSTRUCTIONS ON CABLE SCREENING, ROUTING AND TERMINATION GIVEN IN THIS MANUAL MUST BE FOLLOWED.

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Pt.1-4 24685034

Part 1 Contents

Chapter 1 Introduction to the Hydrastep 2468 Electronic

Gauging System Chapter 2 2468CB & 2468CD Dual Power Supply Version Chapter 3a 2468 - Relay Output Board Option Chapter 3b Delay Relay Output Board Option Chapter 3c 2468 Opto-isolated Output Board Option Chapter 4 Remote Display Options 24683B C & D

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Hydrastep 2468CB and 2468CD Manual Introduction to the Hydrastep 2468 Electronic Gauging System

Introduction to the Hydrastep 2468

Electronic Gauging System

Contents

Page No.

1.1 WATER LEVEL MEASUREMENT .......................................................... 3

1.2 HYDRASTEP 2468 ELECTRONIC GAUGING SYSTEM ....................... 5

1.2.1 INPUT BOARDS .................................................................................. 5

1.2.2 DISPLAY BOARDS .............................................................................. 5

1.2.3 SYSTEM FAULTS (2468CB OR 2468CD) ........................................... 6

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1.3 SYSTEM OPTIONS ................................................................................. 6

1.3.1 OUTPUT BOARDS .............................................................................. 6

1.3.2 REMOTE DISPLAY UNITS .................................................................. 6

1.3.3 OPTION DETAILS ................................................................................ 6

1.4 HYDRASTEP 2468 UPGRADE PATHS AND AVAILABLE OPTIONS .. 7

Illustrations

Figure 1.1 - Front panel of the Hydrastep 2468 gauging system, with local display .......... 2

Figure 1.2 - Schematic of resistance measuring cell and electrodes ................................. 3

Figure 1.3 - Typical Hydrastep 2468 System Installation.................................................... 4

Tables

Table 1.1 - Upgrade paths and available options ............................................................... 7

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Introduction to the Hydrastep 2468 Electronic Gauging System Hydrastep 2468CB and 2468CD Manual

0040

Figure 1.1 - Front panel of the Hydrastep 2468 gauging system

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Hydrastep 2468CB and 2468CD Manual Introduction to the Hydrastep 2468 Electronic Gauging System

1.1 WATER LEVEL MEASUREMENT

The Hydrastep 2468 Electronic Gauging System is designed as an electronic alternative to water level gauges on boilers, giving a more reliable and safer water level indication than conventional visual gauges. It uses the significant difference in resistivities of water and steam in temperatures up to 370C (698F) to determine the water level.

Figure 1.2 - Schematic of resistance measuring cell and electrodes

A vertical row of electrodes is installed in the water level column attached to boiler and typically aligned so that half the electrodes are above and half below the normal water level (see Figure 1.2). The resistance measurement is made between the insulated tip of each electrode and the wall of the column.

The “cell constant” defining the actual resistance measured is determined by the length and diameter of the electrode tip and the column bore. In practice, the cell constant is chosen so that the resistance in water is less than 100k ohms and the steam resistance is greater than 10M ohms. Since the resistivities of water and steam are substantially different, the system is simple and requires no setting up adjustments. It is not susceptible to power supply variations, ambient temperature changes, etc., resulting in a highly reliable system.

A general overview showing how a typical Hydrastep 2468 System is installed is illustrated in Figure 1.3.

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Introduction to the Hydrastep 2468 Electronic Gauging System Hydrastep 2468CB and 2468CD Manual

Figure 1.3 - Typical Hydrastep 2468 System Installation

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Hydrastep 2468CB and 2468CD Manual Introduction to the Hydrastep 2468 Electronic Gauging System

1.2 HYDRASTEP 2468 ELECTRONIC GAUGING SYSTEM

The Hydrastep 2468 is a sophisticated and flexible electronic gauging system. It is supplied in two main versions:

 A Single Power Supply System with Local Level Display  A Dual Power Supply System with Local Level Display

For both systems, the printed circuit boards are housed in the same enclosure, al lowing customers full capability to expand their system as and when conditions dictate.

Table 1.1 on page 1.7 is a summary of all upgrade paths and options for the Hydrastep 2468 system.

1.2.1 INPUT BOARDS

All versions of the Hydrastep 2468 unit contain one or two input boards. The input boards mount on to the base plate in the enclosure. Each input board provides power supplies, electrode drive, signal processing, fault analysis and an analogue output.

The input board can accept inputs from 8, 10, 12, 14 or 16 electrodes. When two input boards are used (in a ‘dual power supply’ system) the electrodes are ‘interlaced’; that is, the odd numbered electrodes are connected to one input board and the even numb ered electrodes are connected to the other. Full details of the wiring are covered in Chapter 2 under Installation.

Each input board also includes a current output circuit that provides an analogue representation of the water level in the column. The analogue output can be configured to give a current output in one of the following ranges:

 0 to 20mA  4 to 20mA  20 to 0mA  20 to 4mA

1.2.2 DISPLAY BOARD

The display board is mounted on to the hinged lid of the unit and provides indication through the viewing window on the enclosure. It also supplies configuration information to the input board(s); that is, the number of electrodes connected to the unit and the required water/steam switching threshold.

Figure 1.1 shows the local display with water level and system fault indication. Water level is indicated by two columns of LEDs, one red to indicate steam and one green to indicate water. The number of LEDs illuminated is dependent on the number of electrodes present and a blanking panel is available to mask the LEDs not used. In addition to the system fault indication is an opto-isolated system fault output. Switches are provided to allow the number of electrodes to be selected (8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30 or 32). Two solder link pads are provided to select the water/steam switching threshold (0.6S/cm or

1.6S/cm).

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Introduction to the Hydrastep 2468 Electronic Gauging System Hydrastep 2468CB and 2468CD Manual

1.2.3 SYSTEM FAULTS (2468CB OR 2468CD)

System fault indication, a yellow LED and an opto-isolated output, is provided for a ‘water

above steam’ condition, an electrode fault or wiring failure and the detection of an internal fault. A further fault is indicated when the electrode number switch is incorrectly set. This fault is indicated by a chequered display of red and green LEDs on the level display.

Faults and their remedies are covered in Chapter 2 under ‘Fault Analysis & Corrective Action’.

1.3 SYSTEM OPTIONS

1.3.1 OUTPUT BOARDS

Each input board can accept one or two output boards that can be used for water level signalling, alarm or trip functions. Each output board provides four relay outputs or four optoisolated outputs. The first output board is fitted directly on top of the input board using three nylon pillars. A second output board (when required) can be fitted on top of the first output board using the same type of fixture. The various output boards are described in Chapter 3.

1.3.2 REMOTE DISPLAY UNITS

Provision is made to drive Remote Display Units. The display board is capable of driving up to 6 remote display units. Only one of these can be powered by the Hydrastep unit, any additional remote displays must be locally powered.

A remote display unit ‘mimics’ the display on the Hydrastep 2468 and is as described in Chapter 4.

1.3.3 OPTION DETAILS

1. Relay Board 24680504 has 4 fully configurable relay outputs Chapter 3a

2. Relay with Time Delay board 24680509 has 4 fully configurable relay outputs Chapter 3b

3. Opto-isolator board 24680505 has 4 full y configurable opto-isolated outputs Chapter 3c

4. Remote Display 24683B. Panel mounted DIN size 8 to 32 electrode display Chapter 4

5. Remote Display 24683C Panel mounted large LED 8 to 32 ele ctrod e display Chapter 4

6. Remote Display 24683D Wall mounted splash proof version of 24683C Chapter 4

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Hydrastep 2468CB and 2468CD Manual Introduction to the Hydrastep 2468 Electronic Gauging System

1.4 HYDRASTEP 2468 UPGRADE PATHS AND AVAILABLE OPTIONS

Table 1.1 describes the available versions of the Hydrastep 2468 Electronic Gauging System and their possible options.

Existing System

2468 CA or 2468 CC

16 point EGS with local display

Single power supply.

2468 CB or 2468 CD

32 point EGS with local display

Dual power supply.

Available Options

Description Part No.

Relay output board Time delay relay

output board Opto-isolated

output board Remote display

unit Input board

upgrade (ac)

Input board upgrade (dc)

Relay output board Time delay relay

output board Opto-isolated

output board Remote display

unit

24680504C 24680509B

24680505A

24683B, C, or D

24680501C

24680516B

24680504C 24680509B

24680505A

24683B, C, or D

Comments

} } } Up to two boards (of any one } type) can be fitted. } }

Up to 6 can be used

Provides an additional power supply (ac mains source) and 16 point input circuit. Upgrades 2468CA to 2468CB.

Provides an additional power supply (24V dc source) and 16 point input circuit. Upgrades 2468CC to 2468CD.

} } } Up to four boards (of any one } type) can be fitted. } }

Up to 6 can be used

24685034

Note: If required, a 24680501C board can be fitted to a 2468CC (or a 24680516B board

can be fitted to a 2468CA) to upgrade to a 2468CE. The 2468CE is a 32 point Electronic Gauging System (EGS) with one ac mains source power supply and one 24Vdc source power supply.

Table 1.1 - Upgrade paths and available options

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2468CB & 2468CD

Dual Power Supply Version

Contents

Page No.

2.1 INTRODUCTION ....................................................................................... 2-3

2.2 ELECTRODE CABLING SYSTEM ........................................................... 2-3

2.3 ELECTRONIC ENCLOSURE .................................................................... 2-3

2.3.1 INPUT BOARD (PCB 24680501 AND PCB 24680516) ......................... 2-5

2.3.1.1 Analogue Output Drive Capability ........................................... 2-5

2.3.2 REMOTE DISPLAY DRIVE CAPABILITY .............................................. 2-5

2.3.3 DISPLAY BOARD (PCB 24680515)....................................................... 2-6

2.3.3.1 Link LK1 .................................................................................. 2-6

2.3.3.2 Links LK2, LK3, LK4 and LK5 ................................................. 2-7

2.3.4 PCB INTERCONNECTIONS .................................................................. 2-7

2.4 INSTALLATION ........................................................................................ 2-8

2.4.1 MECHANICAL INSTALLATION ............................................................. 2-8

2.4.2 ELECTRICAL INSTALLATION ............................................................. 2-10

2.4.2.1 Electrode Connections .......................................................... 2-10

2.4.2.2 Connecting Cables to Water Column Electrodes ................. 2-11

2.4.2.3 Connecting the Electrode Cable Assemblies to 2468

Enclosure………………………………………………………....2-12

2.4.2.4 Hydrastep Power Supply Cables .......................................... 2-13

2.4.2.5 Analogue Output Connection ................................................ 2-15

2.4.2.6 Opto-Isolated Fault Output Connection ................................ 2-16

2.5 SYSTEM CONFIGURATION .................................................................. 2-17

2.5.1 INPUT BOARD (PCB 24680501 OR 24680516) ................................. 2-17

2.5.1.1 Analogue Output Configuration ............................................. 2-17

2.5.1.2 Pulsed Output Setting ........................................................... 2-18

2.5.1.3 Electrode Error Configuration ............................................... 2-18

2.5.1.4 Configuring the Unit to Detect Electrode Error ..................... 2-19

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2.5.2 DISPLAY BOARD 24680515 ............................................................... 2-20

2.5.2.1 Link LK1 Setting .................................................................... 2-20

2.5.2.2 Configuring the ‘Number of Electrodes’ Switch .................... 2-20

2.5.2.3 ‘Switching Threshold’ Setting ................................................ 2-22

2.5.2.4 ‘Compatibility’ Setting ............................................................ 2-22

2.6 FAULT ANALYSIS & CORRECTIVE ACTION ....................................... 2-23

2.6.1 COMPONENT REPLACEMENT .......................................................... 2-30

2.6.1.1 Removing the Input Board (24680501 or 24680516) ........... 2-30

2.6.1.2 Refitting the Input Board ....................................................... 2-30

2.6.1.3 Removing the Display Board 24680515 ............................... 2-30

2.6.1.4 Refitting the Display Board ................................................... 2-30

2.6.2 PARTS LIST - HYDRASTEP 2468 CB & CD VERSIONS ................... 2-31

2.7 SPECIFICATION ..................................................................................... 2-32

Illustrations

Figure 2.1: Outline drawing showing PCB layout and interconnections ............................... 2-4

Figure 2.2: Installation diagram for Hydrastep 2468 Electronic Gauging System unit ......... 2-9

Figure 2.3: Enclosure cable layout for 16 electrode system ............................................... 2-12

Figure 2.4: Voltage Selection (240V or 110V) .................................................................... 2-14

Figure 2.5- Location of display board links LK1 to LK5 & switch SW1 with configuration…..….

details………………………………………………………………………………….2-21

Figure 2.6- Split pads SP1, SP2, SP5 & SP6 locations and settings ................................. 2-22

Tables

Table 2.1 - Analogue output configurations ...................................................................... 2-17

Table 2.2 - Number of electrodes being displayed ........................................................... 2-20

Table 2.3 - Fault analysis/corrective action chart ............................................................. 2-23

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Hydrastep 2468CB and 2468CD Manual 2468CB & 2468CD Dual Power Supply Version

2.1 INTRODUCTION

This chapter introduces the dual power supply version of the Hydrastep 2468 Ele ctronic Gauging System, its mechanical installation, system configuration, simple fault analysis/corrective action capability and its specification.

2.2 ELECTRODE CABLING SYSTEM

This system can have 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30 or 32 electrodes and uses 18-core electrode cables. The cables consist of nine pairs of coloured cores with the black cores in each cable used for the EARTH terminations. Each electrode requires one pair of cores, one core for the signal drive and one for the signal return.

Number of Electrodes

10-16 18-24 26-32

The electrode cable is pre-formed for simple installation. The connections to the electrodes are terminated on the connection stud of the electrode. Either core can be connected to the electronic enclosure as the signal drive or return.

Number of Cables

2.3 ELECTRONIC ENCLOSURE

The basic arrangement of boards in the electronic enclosure is as follows:

 Two input board s su pply power to the system and to the input signal processing

circuits. These boards are: PCB 24680501, ac (mains) input, or PCB 24680516, dc input. One board is mounted on the right hand side of the base plate and receives the odd numbered electrode inputs. The other board is mounted on the left hand side of the base plate and receives the even numbered electrode inputs.

 A display board (PCB 2468 0515) contains the LED drive circuits for the two columns

(32 red LEDs and 32 green LEDs) and the system fault LEDs. This board is mounted on the rear of the front panel, with the LEDs protruding through the front panel.

Required

1 2

3 or 4

 Up to four output boards, Relay Board (P CB 24680504), Relay with time delay Board

(24680509) or Opto-isolator Board (PCB 24680505) may be fitted, two per input board. Output board mounting pillars are fitted to each input board during manufacture to support the first output board mounted.

Refer to Figure 2.1 on page 2-4 for an annotated view of the internal layout of the unit.

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Figure 2.1: Outline drawing showing PCB layout and interconnections

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2.3.1 INPUT BOARD (PCB 24680501 AND PCB 24680516)

The input board processes the electrode inputs to provide water level data for display purposes and a current output representing the water level. Fault detection is also carried out where the condition of the electrode inputs are examined and a FAULT is indicated when:

1. An open circuit in either of the electrode conductor cores is present.

2. A short circuit to EARTH on either the electrode or conductor cores.

3. A water above steam condition exists.

4. An internal circuit fault condition exists.

A current output circuit is also provided on each input board. This gives an analogue representation of the water level. The sense (forward or reverse) and type (0-20mA or 4-20mA) is selectable and described in Section 2.5 of this chapter. Fault indication on the analogue output is an oscillating waveform (of approximately 0.5 Hz) superimposed on the main analogue signal.

The electrode inputs to each input board are passed to the other input board so that each analogue circuit can output the full range content of electrode input signals. However, should either of the input boards fail, the remaining board recognises that data is missing and doubles its own electrode input signal to remedy the data loss giving a maximum error of ± 1 electrode.

Provision is made on each input board to accept one or two output boards, either relay outputs or opto-isolated outputs. Both types of output board are offered as options.

Each input board produces the power supplies for the whole instrument which are derived either from the local mains voltage supply of 110V ac or 240V ac nominal for the 24680501 input board or 20V dc to 40V dc for the 24680516 input board.

Apart from the input voltage there are two other differences between the AC (24680501) and DC (24680516) input boards. These are the analogue output drive capability and the remote display drive capability.

2.3.1.1 Analogue Output Drive Capability

With the minimum DC supply voltage of 20V for the DC input board (24680516) the maximum load that can be driven by the analogue output is 500.

At the minimum mains input voltage the AC input board (24680501) the maximum load that can be driven by the analogue output is 600.

2.3.2 REMOTE DISPLAY DRIVE CAPABILITY

The remote display drive capability is only a consideration when the 2468C is providing power for a remote display. With either input board the unit is capable of driving six remote displays at up to 1000m (3280ft) from the unit but only powering one remote display (any others must be locally powered). With the AC input board the maximum cable loop resistance to the remote display is 27 whilst with the DC in put the maximum cable loop resistance to the remote display is 7. (See remote display section for more details).

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2.3.3 DISPLAY BOARD (PCB 24680515)

The display board receives its power supplies and electrode data from the input boards. This data is decoded and used to illuminate the required LEDs mounted on the display board. The data is also converted to serial format for transmission to remote display units.

The water level in the column is indicated on the front panel by two columns of 32 LEDs, one green column to indicate the electrodes which are in water and one red column to indicate the electrodes which are in steam. The number of LEDs illuminated is dependent on the number of electrodes being used in the system. When 8 to 16 electrodes are being used, the unit illuminates two LEDs per electrode. When between 18 and 32 electrodes are being used, the unit illuminates one LED per electrode. In both cases, the display is top biased (unused LEDs are at the bottom of the display). A blanking label is provided to mask any LEDs that are not used.

The system fault is indicated by the yellow LED. Provision is also made for external indication of a system fault. This takes the form of an opto-isolated output which is normally in its short-circuit state. When an alarm condition exists, the opto-isolated output is opencircuited.

Full illumination of the Fault LED indicates a water above steam condition has been detected. Illumination of half the Fault LED indicates an electrode, wiring or input board related fault. The top half of the Fault LED illuminates when faults are detected by the left hand input board (the even electrodes) and the bottom half of the Fault LED illuminates when faults are detected by the right hand input board (the odd electrodes). Faults are covered under “Fault Analysis & Corrective Action” in section 2.4 of this chapter.

The switch that sets the number of electrodes to be scanned is also mounted on this board. A ‘chequered pattern’ is displayed by the RED and GREEN columns if an invalid switch setting is made on the number of electrodes switch.

The water/steam switching threshold (0.6S/cm or 1.6S/cm) may be changed by solder split pads.

2.3.3.1 Link LK1

The display board caters for both single input board and dual input boards versions of the Hydrastep 2468 system. With dual input boards, the odd electrode inputs are connected to one half of the display board circuit with the even electrode inputs connected to the other half of the circuit.

With the single input board, only one half of the board is connected to the odd and even electrode inputs. In this case the link LK1 must be fitted to connect the odd and even halves of the display board circuit.

Note: This link MUST be removed for the dual input board system.

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2.3.3.2 Links LK2, LK3, LK4 and LK5

These links are used to select either the 8 - 16 display mode (two LEDs per electrode) or the 18 - 32 display mode (one LED per electrode).

Two link headers are provided with the unit and must be fitted in either LK2 and LK4, to enable the 8 - 16 electrode mode, or LK3 and LK5, to enable the 18 - 32 electrode mode.

No. of Electrodes used Link Headers fitted

8 - 16 electrodes LK 2 & LK 4

18 - 32 electrodes LK 3 & LK 5

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