Martek Mark 25 Instruction Manual

Martek Instruments, Inc.

Mark 25

Dissolved Oxygen
Analyzer

Instruction Manual

WARRANTY POLICY

Unless otherwise stated, MARTEK INSTRUMENTS, INC. warrants this equipment
to be free from defects in material and workmanship and to perform in
accordance with applicable specifications for five years (one year for portable
equipment) from date of shipment. All conductivity sensors are guaranteed for
life.

MARTEK will provide free service at the factory, including parts, labor and
transportation back to the customer, for any malfunction of its products which
are returned transportation charges prepaid.

Customers desiring to return a product to MARTEK for repair should contact the
Service Department by telephone at [phone] or fax [phone] or via
our website at www.martekinstruments.com to obtain return authorization. The
information required at this time will be the complete model number and serial
number of the product and a brief description of the problem.

All shipments to MARTEK must be freight prepaid and addressed as follows:

MARTEK INSTRUMENTS, INC.
2609 Discovery Drive
Raleigh, NC 27616
Attn: Repair Department

A complete and detailed statement of the reason for return must accompany the
unit. If possible, include a copy of sample reading or a printout.

Returned units must be packed as well as they were when first shipped. If
possible, use the original packing. Do not return detachable cords or manuals
with the unit.

MARTEK reserves the right to void this warranty if the product has been
subjected to misuse, neglect, accident, improper installation or application, and
for consumable items such as batteries, membranes, or solutions.

This warranty is expressly in lieu of all other obligations or liabilities on the part
of MARTEK. MARTEK neither assumes nor authorizes any other person or
organization to assume on behalf of Martek any other liability in connection with
the sales or use of MARTEK instrumentation.

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MARK 25 TABLE OF CONTENTS

1. IntroductionPage

1.1 Description ……………………………………………………………………………….3

1.2 Specifications ……………………………………………………………………………4

2. Installation

2.1 Panel Cutout for Monitor ..………………………………………………………………5

2.2 Sensor & Flow Chamber Dimensions ..………………………………………………. 5

2.3 Electrical connections to the monitor ……………………………………………….…6

3. Operation

3.1 Keyboard & display ……………………………………………………………………….7

3.2 The CALIB Key...…….….…………………………………………………………………8

3.3 Calibrating Temperature.…………………………………………………………………8

3.4 Calibrating Dissolved Oxygen ..………………………………………………………….9

3.5 Setting Alarms…………….. …….………………………………………………………..9

3.6 Setting Recorder Outputs….……………………………………………………………10

3.7 Setting the Password..…….…………………………………………………….……….11

3.8 Setting the ID Number…………………….……………………………………………..11

3.9 Changing the Serial Output……………………………………………………….……..11

3.10 Setting the Auto-Ranging Function….…………………………………………….….12

3.11 Troubleshooting……………………….…………………………….…………………..13

2

1. Introduction

1.1 Description

The Mark 25 Dissolved Oxygen Analyzer is a simple, low cost, 4 channel,
microprocessor-based monitoring system designed for ultrapure water applications. The
system consists of a readout module that can be used with up to four galvanic-style
dissolved oxygen sensors; each sensor being placed into a separate flow chamber.

A large 4 digit LED display indicates either temperature, parts-per-million (ppm) or
parts-per-billion (ppb) dissolved oxygen. An 8-key membrane keypad allows the
operator to quickly setup and calibrate the analyzer.

The Mark 25 measures dissolved oxygen in four ranges; 0-20 ppb, 0-200 ppb, 0-2
ppm, and 0-20 ppm. Automatic calibration within the Mark 25 provides a fairly reliable
measurement. However, comparison to a referee system remains the most accurate
method of calibration available. (Please refer to Martek’s Mark 21 Portable Dissolved
Oxygen Analyzer for further information).

Four alarm set points with relay contacts are standard in addition to four analog
recorder outputs (0-20 mA) and a serial RS232 digital output for hookup to external
recording equipment. For maximum flexibility, alarm set points and analog outputs

can be assigned to any range on any parameter on any channel.

Housed in a ¼ DIN corrosion-resistant plastic case, the readout module can be panel
mounted with a minimum of tools. The analyzer accepts power inputs from 97 to 240
VAC 50/60 Hz or 24 Vdc and comes with an ON/OFF switch located on the rear panel.
Alarm and recorder wires are easily installed in removable terminal strips.

Sensors connect via a DB-9 connector located on the rear panel of the Mark 25 and the
sensors mount easily to any flat surface. In addition, Martek offers adapter plates
specifically designed to cover the space occupied by other brands of conductivity
analyzers.

Sensors come standard with 6 feet (2 meters) of cable.

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1.2 Specifications

ParameterRangeAccuracyResolution

Dissolved Oxygen0-20.00 ppb+0.1 ppb 0.01 ppb

0-200.0 ppb+1.0 ppb 0.1 ppb
0-2.000 ppm+0.01 ppm 0.001 ppm
0-20.00 ppm+0.1 ppm 0.01 ppm

Temperature0-50.0o C+0.1o C 0.01o C

Power: 97-240 VAC, 50/60 Hz, 24Vdc, fuse protected
Recorder Output: Four, scaleable 0-20 mA DC analog & RS232C serial ASCII digital output
Alarm Output: Four solid-state relays, 5 amp, 250 V
Weight: 2 lbs (0.9 kg) including one sensor with 6 feet (2 meters)
Construction: Readout Module Case: ABS plastic, NEMA 12 (IP65)

Sensor: Type 316 Stainless Steel, Delrin, CPVC, Platinum & lead, Teflon

Cabling: 8-conductor, 24 gauge, PVC jacket, shielded, 0.25 inch (0.63 cm)
Dimensions: ¼ DIN case, 6.51 x 3.78 x 3.78 (165.5 x 96 x 96 mm) LWH

Installation: Panel mount (mounting hardware included). Recommend mounting flow chamber

and sensor vertically.

Flow rate: 50-250 ml/min

4

2. Installation

2.1 Panel Cutout for Monitor2.2 Flow Chamber Mounting
Bracket

3.60” 2.20”

.266” dia.

3.60” 2.00”

1.25”

Panel Cut-out

2.3 Sensor & Flow Chamber Dimensions

2.25”

4.25” 3.50”

5

2.4 Electrical connections to the monitor

Alarm OutputsRecorder Outputs

RS232
Digital Output

RS232 1 2 3 4

ON/OFF
Switch

AC Cord

Sensors

To set up the Mark 25 for operation, simply plug the sensor connector in, then plug the
AC power cord into a properly grounded outlet. If recorder, digital or alarm outputs are
to be used, make certain the Mark 25 is unplugged before connecting the cable to the
appropriate recorder or computer. Follow the wiring diagram below for hooking up the
Mark 25 alarm and analog recorder outputs:

ALARM RECORDER

Channel 1 NO/NC Channel 1 4-20 mA

COMMON

Channel 2 NO/NC Channel 2 4-20 mA

COMMON

Channel 3 NO/NC Channel 3 4-20 mA

COMMON

Channel 4 NO/NC Channel 4 4-20 mA

COMMON

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3. Operation

o

3.1 Keyboard and display

The Mark 25 front panel consists of a
4 digit red LED display, 3 parameter and
channel LED’s, an alarm LED, and an 8­key keypad. The display is used to
present all parameter measurements,
operator prompts and system errors.

o

C

PPM ALARM

PPB

DISSOLVED OXYGEN ANALYZER

READ Range CALIB

C

PPM
MED

PPB
HIGH
RUN

LOW

ZERO

SPAN

www.martekinstruments.com

The keys are arranged in two rows, four
keys in each row.

READ key - When the <READ> key is
pressed, the Mark 25 will display rd. If
one of the bottom keys is selected, the
parameter high-lighted in red will be
displayed and its corresponding LED lit.

RANGE key - Range changes can be
made manually for dissolved oxygen. To
display and/or change the range, press
the <RANGE> key, then select one of
the following keys:

LOW = rG 1: 0-20 ppb
MED = rG 2: 0-200 ppb
HIGH = rG 3: 0-2 ppm
DOWN ARROW = rG 4: 0-20 ppm
UP ARROW = rG A: Auto-ranging

NOTE: Manually changing the range for
dissolved oxygen changes the analog
recorder output scaling. See Section 3.6
for details.

The top row of keys consist of three
color-outlined function keys and are
used to perform instrument operations
such as selecting which parameter to
view, what range the parameter is to be
viewed in, parameter calibration and
system set up.

The bottom row of keys are multi­colored, multi-legend keys and are used
in conjunction with the function keys.
The same colored legends correspond
to the same colored function key.

The arrow keys are used to view
channels, select functions during setup
and calibration, and increment or
decrement a displayed value.

Viewing a different channel is easily
done by pressing the <UP> or <DOWN>
arrow key. The parameter LED’s to the
left of the Mark 25 display also indicate
which channel is being viewed. Channel
ID’s are as follows:

Red LED - Channel 1
Green LED - Channel 2
Red/Green LED - Channel 3
Flashing Red LED - Channel 4

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3.2 The CALIB key

All setup and calibration functions are
conducted via the <CALIB> key. The
<CALIB> allows you to set the following:

• Calibrate temperature and
dissolved oxygen

• Assign and set alarm points

• Assign and set recorder outputs

• Set a password

• Set up an analyzer ID and serial

output

The Mark 25 can be calibrated
automatically or manually for
temperature.

NOTE: Automatic, electronic calibration
is a less accurate method of calibration.
For best results, the Mark 25 should be
calibrated to ASTM or NIST- traceable
standards.

To calibrate temperature, press the
<CALIB> key. The display will flash oC.

To select temperature, press the <UP
ARROW> key. The flashing will stop.
Next, press the <ZERO> key. The Mark
25 will display three calibration bars and
automatically zero the temperature
before returning to the monitoring mode.

Once the sensors have been connected
to the Mark 25, the power cord can be
plugged into any outlet supplying 97-240
V AC 50/60 Hz power. When the Mark
25 is switched on, it will immediately
start monitoring temperature.

Pressing the <CALIB> key will cause
the Mark 25 to display a flashing oC.

If you continue pressing the <DOWN
ARROW> key the display will flash the
following prompts: dO, ALA, rEC, PAS,
uSr. After uSr, the Mark 25 returns to
monitoring temperature.

Here are two basic rules to remember
when using the <CALIB> key:

1. Pressing the <UP ARROW> key will
select any flashing prompt.

2. Pressing the <RUN> key will return
the Mark 25 to the monitoring mode.

3.3 Calibrating Temperature

To span temperature, press the
<CALIB> key, then the <UP ARROW>
key when the temperature prompt is
displayed. Next, select the <SPAN> key.
The Mark 25 will display Aut which is
short for Automatic.

To automatically calibrate temperature,
press the <UP ARROW> key. After the
calibration bars appear, the Mark 25 will
briefly display a span temperature of

50.0 before returning to monitor mode.
The Mark 25 has now been calibrated

for temperature.

To manually calibrate temperature,
simply press the <DOWN ARROW> key
when Aut is displayed. The Mark 25 will
momentarily display three lines, then a
number indicating the input voltage will
appear in the display. Once this number
has stabilized, press the <CALIB> key
and select the appropriate span value
using the up or down arrow keys (the
display defaults to 25 deg. C). When
complete, press the <CALIB> key to

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enter the data into the Mark 25’s
memory.

3.4 Calibrating Dissolved Oxygen

Calibrating dissolved oxygen follows the
same procedure as the temperature
calibration. However, there are several
differences.

Press the <CALIB> key, then the
<DOWN ARROW> key until dO is
flashing. Follow the same procedure for
zero calibration for dissolved oxygen
that was used for temperature.

To span dissolved oxygen, press the
<CALIB> key and select the D.O.
prompt. Next, press the <UP ARROW>
key when the Aut prompt is displayed.
The Mark 25 will display the calibration
bars then briefly display 20.00 ppm
before returning to the monitor mode.

NOTE: If the auto-ranging function is
OFF while the Mark 25 is monitoring
dissolved oxygen and the measurement
exceeds the current selected range, the
Mark 25 will display Err. If an error
message occurs, you must select a
higher range.

will display three bars. The bars indicate
no alarm set point. Use the <UP> or
<DOWN ARROW> keys to select
temperature (t), or dissolved oxygen
(do). Press the <CALIB> key to select
the desired parameter.

The Mark 25 will then display Lo. To
select a low set point, press the
<CALIB> key. If a high alarm set point is
desired, use the <UP> or <DOWN
ARROW> key to change the display to
hi then press the <CALIB> key to
select.

The Mark 25 will display .000 (dissolved
oxygen is selected) though the decimal
point may vary depending on the range
previously selected.

Use the <UP> or <DOWN ARROW>
key to change the value to the desired
alarm set point. When the desired set
point is reached, press the <CALIB> key
to set and activate alarm.

NOTE: For convenience, pressing the
<RANGE> key will advance the digit left
of the decimal point.

To disable alarm, return the set point
value to .000.

3.5 Setting Alarms

The Mark 25 has four alarm set points
that can be assigned to any parameter
on any channel.

Press the <CALIB> until the display
indicates the alarm prompt, ALA. Next,
press the <UP ARROW> key. The
display will prompt with AL 1 and all
parameter LED’s will be lit. The <UP
ARROW> key can be used to change
the alarm set point to 2, 3, or 4.

To assign a particular alarm set point,
press the <CALIB> key. The Mark 25

Once an alarm set point has been
assigned to a particular parameter on a
channel, it cannot be assigned to
another parameter or channel until it
has been disabled.

When the Mark 25 reaches an alarm
state, the Alarm LED will light and the
alarm relay activate. The factory-set
position for the alarm relays is
NORMALLY OPEN. To change to a
NORMALLY CLOSED position, contact
Martek Instruments.

NOTE: The Alarm LED will blink if there
are active alarms that are not being

9

viewed and will remain steady if the
channel viewed is in an alarm state.

3.6 Setting Recorder Outputs

The Mark 25 comes standard with four
4-20 mA analog recorder outputs and
one RS232 digital output. Like the alarm
set points, the four analog recorder
outputs can be assigned to any range of
any parameter on any channel.
Press the <CALIB> until the display
indicates the recorder prompt, rEC.
Next, press the <UP ARROW> key. The
display will prompt with ou 1 and all
parameter LED’s will be lit. The <UP
ARROW> key can be used to change
the recorder output to 2, 3, or 4.

To assign a particular analog output,
press the <CALIB> key. The Mark 25
will display three bars. The bars indicate
no analog output assigned. Use the
<UP> or <DOWN ARROW> keys to
select temperature (t) or dissolved
oxygen (do).

NOTE: A decimal point will be present
for do which indicates which one of the
four ranges the channel is currently
using. The range can be changed by
pressing the <RANGE> key.

When the desired parameter is
displayed, the standard 4-20 mA output
range can be changed to any value
desired. In addition, a “balance” is
provided to “fine-tune” each end of the
recorder range.

To change the lower end of the recorder
range, press the <ZERO> key. The
Mark 25 will display 4.00. Use the <UP>
or <DOWN ARROW> key to change the
number to the desired value. When the
desired value is reached, press the
<CALIB> key to set the value in
memory.

At this point, the Mark 25 will display

000. This is the “balance”. Use the
<UP> or <DOWN ARROW> key to
change the value in order to make the
lower end of the recorder range agree
with the external recorder. When the
desired balance is reached, press the
<CALIB> key to set the value in
memory.

The same procedure is used to change
and “balance” the upper range of the
recorder output. To exit the menu,
simply press the <RUN> key.

To disable any assigned analog
recorder output, select the particular
output and press the <CALIB> key.
Once the parameter is displayed, use
the <UP> or <DOWN ARROW> keys
until three bars are displayed. Press the
<CALIB> key to disable the output.

Once a recorder output has been
assigned to a particular parameter on a
channel, it cannot be assigned to
another parameter or channel until it
has been disabled.

NOTE: When the auto-ranging function
is OFF, changing a dissolved oxygen
range with an assigned analog output
automatically changes the scaling of the
recorder output to the new range.
When the auto-ranging function is ON,
the assigned analog output will remain
in the range it was assigned to.

When the RS232 digital output is used,
calibration is not necessary. However,
the receiving computer must be set up
to accommodate the Mark 25’s digital
output configuration:

Baud Rate - 9600
Parity - Even
Word length - 7
Stop Bit - 1

10

A communication program such as
PROCOMM or Microsoft HYPERLINK
can be used to write data from the Mark
25 to a computer file which can then be
imported into a spreadsheet program
such as EXCEL or LOTUS NOTES.
The data will be displayed in the
following format:

ID, Chan, Temp, Dissolved Oxygen.

3.7 Setting the Password

The Mark 25 can be assigned a numeric
password to prevent unauthorized
personnel from changing any of the
settings.

Press the <CALIB> until the display
indicates the password prompt, PAS.
Next, press the <UP ARROW> key. The
display will prompt with 1999 and all
parameter LED’s will be lit and flashing.
Use the <UP> or <DOWN ARROW>
keys to change the displayed value to
any number other than 0. When the
desired value has been reached, press
the <CALIB> key to set and activate the
password.

Once the password is enabled, the
display will default to 1999 whenever the
password prompt is selected. To gain
access to any other function, you must
use the arrow keys to scroll to the
correct value password then press the
<CALIB> key.

To disable the password, use the <UP
ARROW> key to move the value to 000
then press the <CALIB> key. The
password function will then be disabled.

3.8 Setting the ID Number

The Mark 25 can be assigned a three
digit numeric ID number that will be
displayed on the digital output.

Press the <CALIB> until the display
indicates the user prompt, uSr. Next,
press the <UP ARROW> key. The
display will prompt with id and all
parameter LED’s will be lit and flashing.
When the <CALIB> is pressed, the Mark
25 will display 000. To assign an ID
number, use the <UP> or <DOWN
ARROW> keys to change the displayed
value to any number other than 000.
When the desired value has been
reached, press the <CALIB> key to set
the ID number.

To disable the ID number, use the <UP
ARROW> key to move the value to 000
then press the <CALIB> key. The ID
function will then be disabled.

3.9 Changing the Serial Output

The Mark 25 provides a standard
RS232 digital output. This output can be
configured in one of two ways:

1. Polling - The Mark 25 will provide the
digital output only when polled by the
host computer.

2. Periodic - The Mark 25 will
automatically provide a digital output
at a 30 second interval.

Press the <CALIB> until the display
indicates the user prompt, uSr. Next,
press the <UP ARROW> key. The
display will prompt with id and all
parameter LED’s will be lit and flashing.
Use the <UP> or <DOWN ARROW>
key to advance to the serial prompt,
SEr. When the <CALIB> is pressed, the
Mark 25 will display PoL. To change the
output to periodic interval, press either

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the <UP> or <DOWN ARROW> key
until the Mark 25 displays PEr.

To return to the monitor mode, press the
<RUN> key.

3.10 Sensor Design & Maintenance

The dissolved oxygen sensor is a
galvanic-style sensor using a platinum
cathode, lead anode, potassium iodide
electrolyte and a gas-permeable Teflon
membrane.

5. Screw the Membrane Ring onto the
Outer Body and gently tighten.

6. Using the dropper from the
electrolyte bottle, carefully fill the
four small flow-through holes located
around the platinum tip of the
Spindle.

7. Fill the Outer Body with electrolyte
just above the interior ledge of the
Outer Body.

The dissolved oxygen sensor consists of
five principle parts:

• Spindle

• Outer body

• Filler Valve

• Membrane Ring

• Teflon Membrane

Refer to the photos at the back of this
manual for additional information.

The sensor is normally shipped dry from
the factory without electrolyte or a
Teflon membrane installed. The
following procedure should be used
when changing the membrane or
replacing the electrolyte.

1. Turn the Filler Valve clockwise until it
stops.

2. Unscrew the black Outer Body
counter-clockwise and remove it
from the gray Spindle. Empty out
any electrolyte still in the Outer
Body.

3. Unscrew the stainless steel
Membrane ring from the Outer Body
and remove the old membrane.

8. With the Filler Valve facing up at a
45o angle, screw the Outer Body
back onto the Spindle and gently
tighten (some electrolyte should flow
out of the Filler Valve).

9. Gently screw out the Filler Valve
until it stops (two or three threads
should be visible).

10. Follow the normal calibration
procedure.

If the dissolved oxygen sensor is not
going to be immediately used, fill the red
vinyl wetting cap with water and place
over the Membrane Ring squeezing as
much air from the cap as possible.

If the sensor is not to be used within two
weeks, empty the electrolyte out of the
sensor, dry all of the parts and store the
probe in a cool place.

Normally, very little maintenance is
required for the dissolved oxygen
sensor and it can operate for weeks,
even months, without the need to
change the electrolyte or membrane,
especially if the sample stream has little
or no dissolved oxygen present.

4. Place a new membrane in the
bottom of the Membrane Ring and
place several drops of electrolyte
onto the Membrane.

However, over time or in a sample
stream with a high dissolved oxygen
content, lead oxide will form on the lead

12

anode portion of the Spindle. A possible
indication of lead oxide build-up is lower
than normal readings due to less
surface area on the lead anode. The
lead strip will appear dull and possibly
have yellow deposits near the edges.

mounted on-line, stainless steel
fittings with ¼ inch stainless steel
tubing is recommended. If the
installation is a portable application,
nylon or heavy-wall Tygon tubing
may be used.

To clean the lead anode, simply take a
toothbrush or plastic scouring pad (i.e.
Scotch-Brite) and gently scrub the lead
anode with distilled water until it shines.
You should also check the platinum
cathode tip and the four flow-through
holes for dirt or debris. If any exists, use
a fine wire to clean the holes.

NOTE: Do NOT scrub the platinum
cathode. However, you can polish the

platinum tip using a polishing cloth.
Lastly, make sure the o-rings used in

the Outer Body, Filler Valve, and Flow
Chamber are intact and in good
condition.

When placing the dissolved oxygen
sensor into the stainless steel Flow
Chamber, follow the steps outlined
below:

1. Gently remove the red vinyl wetting
cap from the end of the dissolved
oxygen sensor.

2. Carefully insert the dissolved oxygen
sensor into the flow chamber until it
rests flush with the top of the
chamber. Any twisting of the probe
should always be clockwise. Place
the locking nut over the dissolved
oxygen sensor cable and secure it
firmly onto the flow chamber.

3.11 Troubleshooting

The Martek Mark 25 represents over
thirty years of experience in water
quality measurements and, as such, has
been designed to provide simple,
reliable operation for many years.

To obtain optimum performance from
the Mark 25, care should be taken to
ensure the sensor has adequate flow
and is free of obstructions. In addition, it
is important to maintain correct
calibration on a regular basis.

Comparison of the Mark 25 to a referee
system is the preferred method of
validation, however, calibration using
the Mark 25’s internal circuitry is also
acceptable.

In the event a problem develops with
the Mark 25 that cannot be resolved
through calibration or maintenance,
contact Martek Instruments directly via
telephone, fax, or e-mail located at our
website, ww.martekinstruments.com.

3. To hook up sample flow to the Flow
Chamber, place the inlet flow on the
left fitting (with the mounting bracket
facing away from you) and the outlet
flow on the right fitting. If the Flow
Chamber is to be permanently

13

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