Omega Products PHH-925 Installation Manual

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User ’s Guide

PHH-925 and PHH-950

pH Meters

Servicing North America:

USA: One Omega Drive, Box 4047

ISO 9001 Certified Stamford, CT 06907-0047

Tel: [phone] FAX: [phone]
e-mail: [e-mail]

Canada: 976 Bergar

Laval (Quebec) H7L 5A1
Tel: [phone] FAX: [phone]
e-mail: [e-mail]

For immediate technical or application assistance:

USA and Canada: Sales Service: 1-800-826-6342 / 1-800-TC-OMEGA

SM

Customer Service: 1-800-622-2378 / 1-800-622-BEST

SM

Engineering Service: 1-800-872-9436 / 1-800-USA-WHEN

SM

TELEX: 996404 EASYLINK: 62968934 CABLE: OMEGA

Mexico and
Latin America:

Tel: (95) 800-TC-OMEGA

SM

FAX: [phone]

En Espan÷ol: [phone] e-mail: [e-mail]

Servicing Europe:

Benelux: Postbus 8034, 1180 LA Amstelveen, The Netherlands

Tel: [phone] FAX: [phone]
Toll Free in Benelux: 06 0993344
e-mail: [e-mail]

Czech Republic: ul. Rude armady 1868, 733 01 Kavrine-Hranice,

Czech Republic
Tel: [phone] FAX: [phone]
e-mail: [e-mail]

France: 9, rue Denis Papin, 78190 Trappes

Tel: [phone] FAX: [phone]
Toll Free in France: 0800-4-06342
e-mail: [e-mail]

Germany/Austria: Daimlerstrasse 26, D-75392 Deckenpfronn, Germany

Tel: [phone] FAX: [phone]
Toll Free in Germany: 0130 11 21 66
e-mail: [e-mail]

United Kingdom: 25 Swannington Road, P.O. Box 7, Omega Drive,

ISO 9002 Certified Broughton Astley, Leicestershire, Irlam, Manchester,

LE9 6TU, England M44 5EX, England
Tel: [phone] Tel: [phone]
FAX: [phone] FAX: [phone]

Toll Free in England: 0800-488-488

e-mail: [e-mail]

OMEGAnetSMOn-Line Service Internet e-mail

http://www.omega.com [e-mail]

It is the policy of OMEGA to comply with all worldwide safety and EMC/EMI regulations that
apply. OMEGA is constantly pursuing certification of its products to the European New Approach
Directives. OMEGA will add the CE mark to every appropriate device upon certification.

The information contained in this document is believed to be correct but OMEGA Engineering, Inc. accepts
no liability for any errors it contains, and reserves the right to alter specifications without notice.
WARNING: These products are not designed for use in, and should not be used for, patient connected applications.

Quick Start. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page ii

Introduction

Electrode Connector Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

LCD Display. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Function Keys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Electrodes

Preparing pH and Ion Selective Electrodes . . . . . . . . . . . . . . . . 4

Preparing Conductivity Cells. . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Connecting Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Using and Storing Electrodes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

pH Electrodes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Solid-State FET Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Ion Selective Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Conductivity Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Meter Operation

Setup Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Standardizing and Measuring pH

pH StandardizatIon Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Standardizing and Measuring pH . . . . . . . . . . . . . . . . . . . . . . . 10

Clearing Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Standardizing and Measuring mV

Relative mV Standardization Menu . . . . . . . . . . . . . . . . . . . . . 12

Clearing Relative mV Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Standardizing and Measuring Ion

Ion Standardization Menu. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Standardizing and Measuring Ion. . . . . . . . . . . . . . . . . . . . . . . 14

Clearing Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Standardizing and Measuring Conductivity

Conductivity Standardization Menu. . . . . . . . . . . . . . . . . . . . . 15

Standardizing and Measuring Conductivity,

Salinity,Resistivity or TDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Clearing Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Temperature Compensation. . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Determining Temperature Coefficients. . . . . . . . . . . . . . . . . . . 18

Datalogging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Appendix A: Power Station and Docking Station . . . . . . . . . . . . . 20

Appendix B: Error Conditions and Troubleshooting . . . . . . . . . . . 22

Appendix C: Basic pH Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Appendix D: Ion Selective Electrode Theory . . . . . . . . . . . . . . . . 26

Appendix E: Conductivity Theory . . . . . . . . . . . . . . . . . . . . . . . . . 27

Appendix F: Determining Isopotential Point . . . . . . . . . . . . . . . . . 28

Appendix G: Meter Specifications . . . . . . . . . . . . . . . . . . . . . . . . 30

Maintenance and Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

i

The following quickly steps you through meter operation.For
detailed instructions on each step,refer to the page(s) indicated.

Step Description Page

1. Install Batteries Install four AA alkaline batteries 1
into the rear battery compartment.

2. Connect Install electrode in the appropriate 5

Electrode connector input on top of the meter.

3. Turn Meter On Press On/Off. 3

4. Select Channel Make sure that the channel selected, 3
A (Twist-Lock input) or B (BNCinput),
matches the electrode connection.
Press channel and select. Note: If no
electrode is connected to channel A
Twist-Lock input,only channel B is
allowed.

5.Set Mode For the channel A Twist-Lock input, 3
the meter automatically recognizes
the electrode connected,and selects
the appropriate modes. For channel B
BNC input,any allowed mode can be
selected.Press mode and select.

6. Standardize Immerse the electrode into a buffer or 9 (pH)
standard and stir.Press std (standard- 13 (ion)
ize) and follow the prompts.Repeat 15 (Conductivity)
this step to enter buffers or standards.

5. Print Press Print to send the measurement 19
to the internal datalog and out to a
printer/computer ( if using the Docking
Station).

Warning: Use of this product in a manner not specified by the

manufacturer may impair any safety protection provid­ed by the equipment.

!

This manual explains the operation of
PHH-925 and PHH-950 meters for obtain­ing pH,mV, ion and conductivity (PHH-

950) measurements.Before beginning,we
recommend that you become familiar
with the various features of your meter:

Electrode Connector Inputs

Twist-Lock: Used for attaching pH/ATC,

FET pH/ATC,conductivity/ATC cells or
ATC (temperature) electrodes with the
waterproof Twist-Lock connector.
BNC: Used for attaching pH,ORP,or ISE
electrodes with BNC connector.
Reference: Used for attaching a sepa­rate reference probe.

Batteries

The meter requires four AA alkaline bat­teries (unless used with the optional
Power or Docking Station).To install bat­teries, slide the compartment cover open
by pressing in and down where indicat­ed.Position the batteries according to
the directional markings and insert.Slide
the cover closed.

Note: Nickel-cadmium rechargeable

batteries can be used,but their
operating life is half that of alkaline
cells, and they cannot be
recharged in the meter.

LCD Display

BNC

Reference Twist-Lock

1

Note: Not all of the following will dis­play at the same time.

Temperature: The meter displays
the measured temperature when
an electrode with ATC or separate
temperature probe is attached.
Shows M when a manually entered
temperature is being used.

Result: Current measurement.
BAT: Indicates that the meter has

10% of battery life remaining
(approximately 4 hours),or AC
indicates that the meter is con­nected to the Docking or Power
Station.

Channel: Indicates result is from A
(Twist-Lock input) or B (BNC input).

Manual Temperature: M indicates
that measurement is using a manu­ally entered temperature in place
of the automatic temperature.(See
page 13).

Date: The meter displays the cur­rent date,either in mm/dd/yy or
dd/mm/yy format.

Buffers/Standards: Shows individual
buffers or standards that have
been entered.

Stability symbols: S indicates the
reading is stable,U indicates an
unstable reading.

Mode: Indicates the meter is in pH,
mV, ion, rel mV,conductivity,resistivi­ty,salinity or TDS mode.

Time: Displays the current time in
either 12 hour AM/PM or 24 hour
format.

Function Keys

A

M 25.0°C

BAT

7.000

A M pH

4.00

7.00

10.00

1/24/97 11:52 AM

S

G

A

I

F

D

J

C

B

E

H

B

C

D

E

F

G

H

I

J

Single Channel Display

21.3°C

7.000

A pH

1.00

B M mg/L F­1/24/97 11:53 AM

Dual Channel Display

S

S

mode: Selects the mode (pH,mV, ISE

temperature,conductivity,resistivi­ty,salinity,or TDS) to use for the
currently selected channel (elec­trode input).

std: Initiates standardization process

for the currently selected mode to
enter pH buffers, ion standards or
conductivity standards.

channel: Selects the channel(s) (electrode

inputs) to display.

slope: Displays buffers or standards and

calibration data in slope display.
Press data to see the time and
date for each calibration point.

print: Outputs the current result or cali-

bration data to the Docking
Station RS232 interface and the
internal datalog.

setup: Calls the setup menu (see Setup).
Up/Down Scrolls when viewing stored data

Arrows: and sets the display contrast.
data: Enters the datalogging menu

(see Datalogging).

enter: Accepts numeric values,menu

selections or pending operations.

on/off: Turns the meter on and off.
clear: Clears an incorrect number entry

or cancels the current operation.

Numeric Enters number s for menu selec-
Keypad: tion, standard entry and other

operations.

+ Enters a negative value.

•: Enters a decimal point.
10X: Enters the exponential part of a

number.

1

4

7

2

5

8

3

6

9

0

+

.

10

x

mode

std channel

slope

print setup

data

enter

on/off

clear

3

Electrodes

The meter allows you to use a variety of
glass membrane (“glass”) pH/ATC elec­trodes,ion selective electrodes,the Field
Effect Transistor (FET) Solid-State pH/ATC
electrode (PHH-925 only),temperature
(ATC) probes,Conductivity/ATC cells (AP50
only),combination electrodes using a BNC
connector,or separate electrode pairs with
BNC connector and reference pin.The
glass pH,FET pH and conductivity cells with
Twist-Lock connector are automatically
detected and identified by the meter.

Preparing pH and Ion Selective Electrodes

Remove the protective end cover or the
soaker bottle from the electrode.Before
first using your pH electrode or whenever
the electrode is dry,soak it several hours in
an electrode filling or storage solution (4
Molar KCl solution) or in a buffer for pH
electrodes.Store and condition ISE’s in the
recommended solutions.

Preparing Conductivity Cells

Remove the protective end cover from the
cell.Rinse the cell with deionized or de­mineralized water.

To measure Use channel (connector)

pH A (Twist-Lock)

or

B (BNC)
ORP (mV) B (BNC)
FET pH A (Twist-Lock)
ISE B (BNC & Reference)
Conductivity A (Twist-Lock)
pH & ISE A (Twist-Lock pH)

and

B (BNC ISE)
pH & Conductivity A (Twist-Lock Cond.)

and

B (BNC pH)

Connecting Electrodes

Note: If you install an electrode with a

Twist-Lock connector,the meter
automatically senses it and selects
the appropriate mode and stan­dardize menus for that type of

electrode.

Glass pH/ATC, FET pH/ATC electrode, con­ductivity/ATC cell or ATC Probe (with
Twist-Lock connector):

Connect the electrode to the Twist-Lock
input located at the top of the meter.Line
up the white arrow and line on the elec­trode’s Twist-Lock connector and push
until it locks in place.To disconnect,twist
the connector ring in the arrow direction
and pull apart.

pH, ORP or ISE electrode (with BNC con­nector):

Connect the electrode to the BNC input
located at the top of the meter.Push in
and rotate the electrode’s BNC connec­tor until it locks in place.To disconnect,
twist the BNC connector in the opposite
direction and pull.

Electrode Pair Using a Reference
Electrode (with Reference Pin Plug):

Connect the indicating electrode to the
BNC input.Connect the reference elec­trode to the Reference input.Push the
electrode’s tip pin plug into the input to
connect and pull out to disconnect.

BNC
Input

Twist Lock
Input

5

BNC
Input

Reference
Input

Using and Storing Electrodes

pH Electrodes

Provide moderate stirring for faster
electrode response.

Rinse the electrode between each
measurement with a portion of the
next sample or buffer to be measured,
or with deionized or distilled water.

Keep glass electrodes wet when not
being used by moistening the cotton in
their end covers with electrode filling
solution and storing them with end
covers on,or by placing in their stor­age vials.

Keeping glass electrodes “wet”will
improve their performance.In the la b,
store electrodes in electrode filling solu­tion or storage solution (4M KCl).For
electrodes used in field applications,
occasionally leave them in solutions for
several hours.

Solid-State FET Electrode

The model PHH-925 allows use of both
standard glass pH/ATC and Solid-State
FET (Field Effect Transistor) pH/ATC elec­trodes.The meter can store a calibra­tion for both types of electrodes.Plug
the FET electrode into the Twist-lock
input. Allow the FET about 2 minutes to
warm up and stabilize when first con­nected.The FET electrode can be
stored dry or in electrode storage solu­tion.If the FET electrode remains con­nected to the meter (and batteries are
in the meter),further warm up is not
necessary.

Ion Selective Electrodes

Add proper amount of Ionic Strength
Adjuster (ISA) to all standards and
samples.

Provide moderate stirring for faster
electrode response.

Rinse the electrode(s) between each
measurement with a portion of the
next sample or standard to be mea­sured,or with deionized or distilled
water.

In the lab, follow the instruction sheets
for the individual electrode.Store as
recommended.

Conductivity Cells

Rinse the cell between each measure­ment with a portion of the next sample
or standard to be measured.

Immerse the cell fully into the standard
or sample to be measured,lift the cell
to allow the solution inside the cell to
drain,and immerse the cell again.
Repeat three times.

Stir briefly and tap the cell against the
container bottom to dislodge air
bubbles.

Clean any deposits from the cell body
by rinsing with deionized water and
store dry.

7

Setup Menu

Press setup to access the menu options.

1. Check batter y - Indicates the bat­tery power remaining.

2. Set sleep mode - Enter the time in

minutes before the meter auto­matically turns itself off (“sleeps”) if
no keystrokes have been pressed.
Enter a value of 0 to keep the
meter on continuously. The maxi­mum time allowed is 999 minutes.

3. Set sample ID# - Select a starting
value for the sample ID number.
Sample measurements will then
be identified by sequential sample
ID numbers. Each time the print
key is pressed the sample number
will be incremented.

4. Set time and date - Enter time and

format,and date and format.

5. Signal averag ing - Set the meter
to very slow (10 readings),slow
(8),medium (6),fast (4) and very
fast (2).The meter places each
new reading into a moving win­dow,from which it calculates the
average (displayed) and standard
deviation (for stability determina­tion).

6. Manual tempera ture - Enter a tem­perature to be used in the
absence of an ATC probe or with
manual temperature override.

7. Set contrast - Adjust the display
contrast.

8. Pr inter baud rate - Select the baud
rate for the RS232

input/output.

Pressing a number key causes that menu
selection to be chosen or that operation
to be executed.

Setup Menu

1 - Check battery
2 - Set sleep mode
3 - Set sample ID#
4 - Set time and date
5 - Signal averaging
6 - Manual temperature
7 - Set contrast
8 - Printer baud rate

pH Standardization Menu

Press mode and select 1 – pH. Press std
and the standardize pH menu appears:

1. Enter a buffer - Allows you to add
a new buffer or update an existing
buffer.Follow the prompts.

2. Clear buffers - Clears all buffers
currently stored.

3. Select buffer set - There are five auto-

recognition buffer sets,one custom
set and manual entry

available.For some buffer sets the
meter will ask for the nominal refer­ence temperature for the buffers set
(the temperature at which the
buffers are at their nominal values;
e.g.,7.000 at 25°C).

Auto-recognition buffer sets - The
five buffer sets are automatically
recognized and temperature cor­rected for the variation of buffer

pH with temperature.
Custom buffers - Allows you to
enter up to five custom buffers
(each at least two pH units
apart), with no temperature com­pensation.
Manual entry - Allows you to enter
any buffer value.

4. Enter slope - Allows you to enter a
known slope to be used by the meter
with a single-point standardization.
The normal default slope is 59.16

mV/pH.The meter allows between 80
and 120 % efficiency to be entered.

5. Temperature source - Allows the

meter to be set to use the ATC if pre-

sent (Auto) or use a manual tempera­ture override (Manual).

6. Set isopoint - Allows you to enter in an

isopotential point (See Appendix F).

7. Resolution - Allows pH readings to be

set to 0.1,0.01,or 0.001 pH units.

9

Auto-recognition

Buffer Sets

• 2, 4, 7, 10,12

• NIST 1.68,4.01,6.86,

9.18,12.46

• 1,3,6,8, 10, 13

• DIN 1.09,3.06,4.64,

6.79,9.23,12.75

• 1,4,7,10, 13

• Custom buffers

Standardize pH

Channel A

1 - Enter a buffer
2 - Clear buffers
3 - Select buffer set
4 - Enter slope
5 - Temperature

source
6 - Set isopoint
7 - Resolution

Note: Dur ing auto-

matic calibration,the

meter allows pH

electrodes with 90 to

105% efficiency to

be used.

Standardizing and Measuring pH

1. Immer se the electrode in a buffer
and stir moderately.The meter dis­plays the current pH measurement.

2. Press std, then press 1–Enter a buffer.

3. Follow the prompts on the display.

4. The meter automatically recognizes
the buffer,waits for a stable signal,
and enters the buffer. The entered
buffer appears in the display.

5. Alternatively,if the signal is not sta­ble,you can press enter when the
reading stabilizes according to your
tolerance criteria.The meter then
enters the buffer.

6. Repeat steps 1 through 3 to enter a
second,third,fourth or fifth buffer.
With more than one buffer the
meter performs a diagnostic check
on the electrode.The electrode is
considered good if the slope is
between 90 to 105%.If a sixth buffer
is entered,the buffer farthest away is
replaced by the new buffer.

Hints: To achieve better accuracy:

• Standardize using at least two buffers ,
bracketing the expected pH of your
samples.

• Standardize at least daily for the most
accurate readings.

• Rinse the electrode with DI water
between samples and buffers.

• Blot the electrode dry (DO NOT rub or
wipe) between samples and buffers.

• Stir all buffers and samples.

• During standardization,allow time for

mV

4 7 10

pH buffers

samples

the electrode to stabilize before enter­ing the buffer into the meter.

• Always use fresh buffers .

Clearing Buffers

Press std, then press 2–Clear buffers to
clear buffers. If all previously entered
buffers will be re-entered,it is not neces­sary to clear buffers.If re-entering only
some buffers, all the old buffers should be
cleared.

The meter automatically compensates for
the temperature dependence of the
electrode’s response when measuring pH.
The meter also compensates for buffer ‘s
change in pH value with temperature.
Temperature compensation is based on
temperature either from an ATC probe or
a manually entered temperature.

11

Actual Buffer pH vs. Temperature

pH 4.00(4.01)/7.00/10.00 buffer (nominal 25°C)

Temperature Buffer 4 Buffer 7 Buffer 10

(°C)

30 4.016 6.991 9.947
25 4.008 7.003 10.000
20 4.003 7.020 10.057
15 4.000 7.042 10.119
10 3.998 7.069 10.187

Millivolt measurements are used to mea­sure ORP (oxidation-reduction potential)
or redox potential,to check perfor­mance of pH or Ion Selective Electrodes,
and for redox titrations.

The meter will measure millivolts (mV) by
selecting mV mode using the mode key.
Relative mV can be measured by enter­ing a mV offset or using a mV value as
the relative mV reference point.

Relative mV Standardization Menu

In mV mode,press std and the standard­ize mV menu appears:

1. Auto-zero relative mV - Sets the rel­ative mV offset equal to the nega­tive of the current mV reading. The
current mV becomes 0.0 relative
mV.

2. Enter manual mV offset - Allows you

to enter in any mV offset.

3. Clear relative mV mode - This
clears any offset that has been
entered,returning the meter to
absolute mV mode.

4. Resolution - Allows mV readings to
be set to 1 or 0.1 millivolt.

Clearing Relative mV Mode

Press std,then press 3 – Clear relative mV
mode to clear offset and return the

meter to absolute mV mode.

Standardize mV

Channel A

1 - Auto-zero

relative mV

2 - Enter manual

mV offset

3 - Clear relative

mV mode

4 - Resolution

Electrode Potential,mV

Titrant Volume, mL

Redox Titration

The PHH-925 and PHH-950 can be used
with Ion Selective Electrodes (ISE’s) to
directly read ion concentrations.ISE’s are
connected to the channel B (BNC) input.
If a separate reference electrode is
required,connect it to the reference
input jack.

Ion Standardization Menu

Select channel B using the channel
key. Press mode and then press 3–ISE
for ion concentration mode.Press std
and the standardize menu appears.

1. Enter a standard - Allows you to
add a new standard or update
(re-enter) an existing standard.
Follow the prompts.With the first
standard you select the ion
name and units.

2. Clear standards - Clear s standards
for the standardization set in current
use.

3. New ion cal - Allows for another set
of calibration standards to be
entered/stored for a different ISE.
The meter stores up to five ion cali­brations.

4. Recall ion cal - Allows the recall of
an ion calibration set.

5. Enter slope - Allows entry of a known
slope to be used with a single-point
standardization.The nor mal default
slope is 59.16 mV/decade for mono­valent ions and 29.58 mV/decade
for divalent ions at 25°C.

6. Temperature source - Allows the
meter to use the ATC (if present) or
a manually entered temperature
override*.

7. Set Isopoint - Allows you to enter an
isopotential point (See Appendix F).

8. Enter blank - Allows you to enter a
blank.

9. Resolution - Allows the readings to
be set to 1,2 or 3 digits.

Standardizing and Measuring Ion

13

Standardize ISE

Channel B

1 - Enter a standard
2 - Clear standards
3 - New ion cal
4 - Recall ion cal
5 - Enter slope
6 - Temperature source
7 - Set isopoint
8 - Enter blank
9 - Resolution

*Temperature Source

Set to Auto to use the
ATC probe (if present).
Set to manual when
samples being mea­sured on one channel
are at a different tem­perature from samples
with the ATC probe.Use
manual when tempera­ture correction is not
desired or the isopoten­tial is not known (ISE’s).

1. Add the appropriate Ionic Strength
Adjuster (ISA) solution to the stan­dard.

2. Immer se the electrode(s) in the solu­tion and stir continuously.

3. Press std and select 1–Enter a stan-
dard to add a standard.

4. Follow the prompts.

5. The meter waits for a stable signal
and enters the standard.The
entered standard appears in the
display.

6. Alternatively,if the signal is not sta­ble,you can press enter when the
reading stabilizes according to your
tolerance criteria.The meter then
enters the standard.

7. Repeat steps 1 through 6 to enter a
second,third,fourth or fifth standard.
With more than one standard,the
meter performs a diagnostic check
on the electrode.

Helpful Hints:

• Provide stirring.

• Allow the electrode time to reach a
stable reading before entering the
standard into the meter.

• To achieve better accuracy,standardize
using at least two standards,bracketing
the expected range of your samples.

• Standardize from low to high concen­trations.

• Always use fresh standards.

Clearing Standards

mV

ion standards

log [ion]

Press std, then press 2–Clear standards
to clear the current set being used.
This will not clear other stored ion cali­brations.
The meter will automatically recognize
when a conductivity cell is attached
to the meter.

Select channel A using the channel
key. Pressing mode allows the meter
to be set to the proper units.

Conductivity modes and units are:

Conductivity - µS/cm or mS/cm.
Resistivity - Ω•cm , kΩ•cm or MΩ•cm
Practical Salinity - salt concentration

in parts per thousand (ppt) based
upon sea water.
NaCl Salinity - sodium chloride equiva­lent concentration in ppt.
Total Dissolved Solids (TDS) - an empir i­cal scale relating conductivity to total
dissolved solids in ppt.

Conductivity Standardization Menu

Press std and the standardize con­ductivity menu appears:

1. Enter standard - Allows you to
add a new standard or re-enter
an existing standard.Up to five
points may be entered.Follow
the prompts.

2. Clear standards - Clears all stan­dards currently stored.

3. Temperature source - Allows the
meter to use the ATC (if present),

or use a manually entered temper­ature override.

4. Enter known cell constant - Allows
you to enter the nominal or known
actual cell constant.

5. Enter tempera ture coefficient -

15

Select Mode

Channel A

1 - Conductivity
2 - Practical

Salinity
3 - NaCl Salinity
4 - Resistivity
5 - Total Dissolved

Solids
6 - Temperature

Standardize

Conductivity

Channel A

1 - Enter a standard
2 - Clear standards
3 - Temperature

Source
4 - Enter known

cell constant
5 - Enter temperature

coefficient
6 - Resolution
7 - Autoranging

Allows you to select the reference
temperature and the temperature
coefficient (used with conductivity).
The default setting is 1.90%/°C cor­rection to 25°C.

6. Resolution - Allows the readings to be
set to 1,2,3 or 4 digits.

7. Autorang ing (Conductivity/

Resistivity modes)- Select unit
autoranging (µS to mS,Ω to kΩ to
MΩ) or fixed units (µS,KΩ).

or

7. Solids factor (TDS mode) - enters the
solids factor used for TDS.The default
is 0.5.

Standardizing and Measuring
Conductivity, Salinity, Resistivity or TDS

1. Immer se the cell in a standard and
stir moderately.The meter displays
the current measurement.

2. Press std, then press 1 – enter stan-
dard to add or re-enter a standard.
Follow the prompts.

3. The meter waits for a stable signal,
and enters the standard.The entered
standard appears in the

display.

4. Alternatively,if the signal is not stable,
you can press enter when the read­ing stabilizes according to your toler­ance criteria to enter the standard.

5. Repeat steps 1 through 3 to enter a
second,third,fourth or fifth standard.
Standards must be at least two-fold
apart in value.On each standard,
the meter performs a diagnostic
check on the cell.The cell is consid­ered bad if the cell constant is out­side 50% and 200% of the nominal

value.

Helpful Hints:

• Always immerse,then drain, the con­ductivity cell several times when
transferring to a new standard or
sample.

• Ta p the cell gently to remove air bub­bles.

• Always use fresh standards.

• Standards are entered in conductivi­ty as µS/cm,in resistivity as KΩ•cm,
and in salinity and TDS as either
µS/cm or KΩ•cm.

• To achieve better accuracy, stan­dardize using at least two standards,
bracketing the expected range of
your samples.

• Verify that the proper cell constant is
being used for the sample’s conduc­tivity (1 or 10 cm-1).

Clearing Standards

1. Press std,then press 2 – Clear stan­dards.

Temperature Compensation

The meter automatically compensates
for conductivity temperature depen­dence when a temperature coefficient
is used.The range of values for the tem­perature coefficient is from 0 to 4%/°C.To
disable temperature compensation,
enter a value of zero.Resistivity is not
temperature compensated,practical
salinity is referenced to 15°C,and NaCl
equivalent salinity is referenced to 25°C.
For conductivity measurements,select a
reference temperature and enter a tem­perature coefficient.

Determining Temperature Coefficients

17

Conductivity

Concentration

The temperature coefficient of a particu-

lar sample can be determined and
entered to allow temperature correc­tion.A typical temperature coefficient
for a simple salt solution is 1.9%/°C.

To determine temperature coefficient:

• Set reference temperature to 25°C
and temperature coefficient to

0.00%/°C.

• Record the conductivity value and
temperature of the solution (tempera­ture must be different than the refer­ence temperature).

• Heat or cool solution to the reference
temperature.

• Record the conductivity of the solu­tions at the reference temperature.

• Solve the following equation for the
temperature coefficient TC.

Datalogging

TC =

Conductivity at T
Conductivity at T

ref

–1

100

T – T

ref

Typical Temperature Corrections for 15°C to 25°C

NaCl Concentration (M) TC (%/°C)

0.5 1.90

0.1 1.96

0.01 2.01

0.001 2.02

KCl

1 1.75

0.1 1.85

0.01 1.90

0.001 1.96

Data

toggles

between

these

screens

The meter will store up to 250 data
points. Press print to store the current
result with units,temperature,time,
date,channel,sample number and
stability to the internal datalog. Print
also outputs an ASCII text string with
the information to the optional
Docking Station RS-232 interface.

Press data and the Datalogging
menu will appear.

1. Star t interval - Allows you to
enter the time interval for auto­matic datalogging.

2. Stop interval - Stops time-based
datalogging.

3. View datalog - Shows the stored
data,one screen at a time.Press
the data key to move side to
side to show time and date for
each sample.Use the arrow keys
to scroll up and down through
the samples.

4. Clear da talog - Clears all the
data points out of memory.

5. Pr int datalog - Allows you to print
all data points.

The optional Power Station provides a
laboratory bench stand and external

19

Minimum Datalogging

Time Interval

With meter continually on:

1 second at 9600 baud
2 seconds at 2400 baud

With meter in sleep mode:

10 seconds

Datalogging

(43 points)

1 - Start interval
2 - Stop interval
3 - View datalog
4 - Print datalog
5 - Clear datalog

View Datalog

(243 points)

5.432 pH A S
#12345 M 25.4C

9.99E-9 mg/L F- B S
#345 100.0C

180.5 mV B S
#3 34.5C

9.500 ion Cl- A S
#12345 100.2C

100.2 µS/cm A U
#12400 55.2C

screen data

View Datalog

(243 points)

5.432 pH A S
5:43PM 12/30/95

9.99E-9 mg/L F- B S
5:43PM 12/30/95

180.5 mV B S
5:43PM 12/30/95

9.500 ion Cl- A S
5:43PM 12/30/95

100.2 µS/cm A U
5:43PM 12/30/95

screen data

AC power.The optional Docking Station
provides external AC power and RS-232
interface to a printer or computer/ter­minal.

Installing Meter in the Station

1. Connect the power supply to the
Power or Docking Station and to
an AC outlet.

2. Place the meter in the station.

3. The meter displays AC to indicate
external AC power is being used.
The Auto-Off feature is suspended
while the meter is in the

station.

Using with a Printer or
Computer/Terminal

1. Connect your serial ca ble from
the Docking Station to the serial
port on your printer or computer/
terminal. See the next page for
wiring requirements.

2. Set pr inter as follows:

• baud rate must match the
meter

• 8 data bits

• no parity

• 1 stop bit

3. Pressing pr int causes the current
reading to be printed.

Note: During standardization,the
meter automatically prints standard­ization data,including the value,
temperature,slope and the time

and date.
The following serial interface
commands are available:

Add standard: 7.ØØ3 pH B 25.ØC 2/17/97 11:47 AM
Add standard: 4.ØØ9 pH B 25.ØC 2/17/97 11:47 AM
Add standard: 1Ø.ØØØ pH B 25.ØC 2/17/97 11:47 AM

4.ØØ9 mS/cm 2/17/97 11:47 AM 25.ØC 99.8

7.ØØ3 mS/cm 2/17/97 11:47 AM 25.ØC 99.7

1Ø.ØØØ mS/cm 2/17/97 11:47 AM 25.ØC

Sample: 1S 1Ø.ØØ1 pH B 25.Ø M 2/17/97 11:48 AM

Add standard: 1.ØØ ppm Cl- B 25.ØC 2/17/97 11:48 AM
Add standard: 1ØØØ ppm Cl- B 25.ØC 2/17/97 11:49 AM
Add standard: 1ØØ ppm Cl- B 25.ØC 2/17/97 11:49 AM
Add standard: 1Ø.Ø ppm Cl- B 25.ØC 2/17/97 11:49 AM
Sample: 2 S 1Ø.Ø ppm Cl- B 25.ØCM 2/17/97 11:50 AM

Clear standards: cond A
Add standard: 1ØØ uS/cm A 25.ØC 2/17/97 11:52 AM
Sample: 3 S 1ØØ uS/cm A 25.ØC M 2/17/97 11:52 AM

Sample: 4 S 1Ø.Ø kOhm CM A 25.ØC M 2/17/97 11:52 AM
Sample: 5 U 1.ØØ kOhm CM A 25.ØC M 2/17/97 11:52 AM

Command Function

KM Mode
KS Standardize
KC Channel
KL Slope
KP Print
KT Setup
KA Up Arrow
KD Data
KB Down Arrow
KN Enter
KO Off
KX Clear
KF ±
KG Decimal Point
KE 10

x

K(digit) Enter numeric dig it

The complete pin connections for the dig­ital I/O connector to the docking station
are below.

Note: Some printers and computer

serial ports will require only pins
1-3 connection.Those requir ing
more extensive handshaking
may require the other pin con­nections.

Testing the Electrode and Meter

21

Docking Pin At
Station Function Computer

1 common 1
2 serial data in 2
3 serial data out 3
4 no connection 4
5 no connection 5
6 no connection 6
7 common 7
8 common 8
9 no connection 9

To test the pH electrode,place it in a fresh
pH 7 buffer.Select the correct channel for
the electrode.Press mode and select mV.
Verify that the meter is in absolute mV
mode (display shows mV,not rel mV) and
note the mV reading.Repeat for either a
pH 4 or pH 10 buffer.If the electrode
potential is within the limits shown,it is
measuring correctly.

pH 7 0 ± 30 mV
pH 4 159 to 186 mV higher than pH 7 reading
pH 10 159 to 186 mV lower than pH 7 reading

To test the meter for correct operation
with a BNC electrode,short the BNC input
connector using a bent paper clip as
shown.Press mode and select mV mode.
If the meter reads 0 ± 0.1 mV*, it is measur­ing correctly.

To test the meter for correct operation
with a pH Twist-lock electrode,shor t the
Twist-lock input connector using two
paper clips as shown.Each paper clip
must touch two adjacent pins inside the
connector.Press mode and select mV
mode.If the meter reads 0 ± 0.1 mV*, it is
measuring correctly.

* Note: Meter accuracy is ±0.1 mV at

calibration temperature,not including

long term drift and a temperature

error.The zero and slope temperature

coefficients of the meter over the

range of 15 to 40°C specify ±4 mV at

full scale (worst case).The long ter m

drift will not exceed 0.1 mV per month.

Error Messages

pH value out of range
The electrode efficiency is outside the

acceptable limits for the pH electrode: 90
to 105%.

The electrode has drifted too far from the
last calibration.

• pH electrode is not in a solution.

• Insufficient or incorrect filling solution
in reference electrode.

• Cracked or broken glass bulb mem­brane.

• Improper electrode conditioning.

• Bad buffers.

• Blocked or clogged reference elec­trode liquid junction.

• Poor technique not rinsing electrodes
between buffers.

• Loose connector or cable.

• Incorrect manual buffer value entry.

• Defective meter.

mV value out of range

• Electrode is not in a solution.

• Defective electrode.

• mV input exceeds the design range
of the meter.

• Defective meter.

Ion value out of range
The electrode slope is outside the

acceptable limits for an ion selective
electrode.

• Ion electrode is not in a solution.

• Bad standards.

• Entry of incorrect concentration.

• Poor technique,not rinsing elec­trodes between standards.

• Not stirring the standards.

• Improper electrode conditioning.

• Defective ISE or reference electrode

• Insufficient or incorrect filling solution

23

in reference electrode.

• Loose connector or cable.

• Defective meter.

The ion standard (mV signal) is too close to
another standard.

• The standards are made too close
together (should be 10 fold apart).

• Bad standards.

• There is no ISA adjuster in the stan­dards.

• Defective ISE or reference electrode.

• Insufficient or incorrect filling solution in
reference electrode.

Conductivity out of range.
Resistivity out of range.
Salinity or TDS out of range.

• Sample too high in conductivity for
meter range with cell constant used.

• Defective probe.

• Defective meter.

Temperature out of range.

• Defective ATC probe.

• Temperature manually entered out­side of -5 to 105°C.

• Defective meter.

The meter has lost calibration coefficients.

• Battery backed memory has been
corrupted. (The memory does not use
the AA batteries for backup.There is a
separate lithium battery inside the
meter.It is

not

user serviceable).

• Factory service is required to re-cali­brate the meter for accurate mV, tem­perature,or conductivity measure­ments. pH, ion or conductivity mea­surements are still accurate after stan­dardization with buffers or standards.

pH Theory

The measurement of pH plays an
important role in water quality, indus­try and research.pH is a measure of
acidity or alkalinity of a solution,and
is usually written:

pH = -log [H+]

Where [H+] is the concentration of
hydrogen ions.

pH levels generally range from 0 to
14,with a pH value of 7 being the
neutral point.pH values above 7 are
alkaline,and pH values below 7 are
acidic solutions.

Conventional pH meters use a glass
pH electrode paired with a refer­ence electrode.The reference elec­trode provides a stable reference
point and completes the electrical
circuit.The pH meter reads the volt­age between the two electrodes,
converts it to pH units,and displays the
result.

The PHH-925 meter can also use a Field
Effect Transistor (FET) electrode for
measuring pH.The FET uses an ion-sens­ing solid state membrane attached to
a transistor to measure the hydrogen
ion concentration of a solution.
The measurement of ions plays an
important role in water quality, industr y,

25

pH
0 Strong Acid
1
2 Lemon Juice
3
4 Tomato Juice
5 Coffee
6

Neutral 7 Pure water

8 Baking Soda
9
10
11
12 Ammonia
13
14 Strong Base

More Acidic

More Basic

pH scale showing the
relative acidity or basicity of
some common substances

research and environmental monitoring.Ion­selective Electrodes (ISE’s) respond,more or
less exclusively, to a specific type of ion in solu­tion.The par ticular ion to w hich an ISE
responds depends on the chemical makeup
of its sensing membrane.ISE’s operate accord­ing to a form of the Nerst equation:

E = Eo+ (2.303 RT/F) log a

Where:

E = measured electrode potential
E o= standard potential of the system (con-

stant)
R = gas constant
F = Faraday’s constant
T = absolute temperature
a = activity of the ion interest in the solution

Conductivity Theory

Conductivity refers to the ability of a
solution to conduct electricity.The
amount of electrolytes present deter­mine the ease with which a solution
can carry a current.

Conductivity is used as a measure of
the purity of water.Pure water contains
few dissolved ions and has a low con­ductivity and a high resistivity. Ultrapure
reagent grade waters are measured in
resistivity. Practical salinity is a measure
of salt concentration in sea water, NaCl
Salinity is the amount of NaCl dissolved
which would give the same conductivi­ty as the sample,and Total Dissolved
Solids (TDS) is an empirical relationship
between conductivity and dissolved
solids in typical samples.

Isopotential Point

27

Conductivity =

1

Resistivity

TDS = Conductivity x Solids Factor

Where C = Conductivity

T = Temperature °C

The Isopotential point is the potential of
an electrode system which does not
change with temperature.Typical pH
electrodes have isopotential points near
zero mV (which is the default setting for
the meter).For high accuracy pH mea­surements,or for ion measurements where
the sample temperature may widely vary,
the isopotential of the pH or ion electrode
may be experimentally determined and
entered into the meter.

• Prepare a set of buffers or ion stan­dards spanning the linear range of
the electrode.Place the buffers or
standards in a temperature bath at
known temperature.

• Place the meter into mV mode.

• Measure and record mV readings of
each pH or concentration,and
repeat at several temperatures.

• Using graph paper,plot the log of
concentration or pH value versus
mV reading.

• Draw lines connecting the points at
each temperature.

Where the lines intersect is the
Isopotential point.

29

200

100

0

10

-3

10

-4

Log of Ion Concentration, moles/L

Electrode

Output

(mV)

10°C

60°C

Isopotential Point:

3.07 x 10-4moles/L, 162 mV

Ion Electrode Isopotential Point

50

150

-180

0

180

4 7 10

pH

Electrode

Output

(mV)

25°C

10°C

Isopotential Point:

7.04pH 9 mV

pH Electrode Isopotential Point

pH

Range: -2.000 to 20.000
Resolution: 0.1/0.01/0.001
Accuracy: ±0.002

mV

Range: ±1,200
Resolution: 1/0.1
Accuracy: ±0.1mV over ±400mV:

±0.2mV over ±1200mV
Zero temperature coefficient: 0.01 mV/°C max.
Scale temperature coefficient: 85ppm/°C max.

Ion

Range: 1.00E-9 to 9.99E9
Resolution: 1,2,or 3 significant figures
Accuracy: 0.17n%; where n equals electrons

exchanged in the electrode reaction

Conductivity

Conductivity 0.01 – 300,000 µS/cm*
Practical Salinity: 0 to 42 ppt*
NaCl equivalents: 0 to 70 ppt*
Resistivity: 33 to 100 megohms*
TDS: 0.005 – 300,000 ppt*
Resolution: 1, 2, 3 or 4 significant figures
Accuracy: ±0.5% of reading ±0.01 µS/cm
Temperature coefficient: 0.001 µS/cm/°C

with cell constant 1.0 cm

-1

Range 5: 30,000 to 3,000 µS/cm
Range 4: 3,000 to 300 µS/cm
Range 3: 300 to 30 µS/cm
Range 2: 30 to 3 µS/cm
Range 1: 3 to 0.3 µS/cm

Temperature

Range -5° – 105°C
Resolution 0.1°C
Accuracy ±0.3°C

* dependent on cell constant

31

Maintenance

Other than battery replacement, this product contains no
user serviceable par ts . All replacement parts other than
batteries should be obtained from Omega Engineering Inc.

Cleaning

The exterior surfaces of this product may be cleaned with a
damp cloth or with mild detergent.

NOTICE

This equipment has been tested and found to comply with
the limits for a Class A digital device,pursuant to Part 15 of
the FCC rules. These limits are designed to provide reason­able protection against harmful interference when the
equipment is operated in a commercial environment.This
equipment generates,uses, and can radiate radio frequen­cy energy and,if not installed and used in accordance
with the instruction manual,may cause harmful interfer­ence to radio communications.Operation of this equip­ment in a residential area is likely to cause harmful interfer­ence in which case the user will be required to correct the
interference at his own expense.

CAUTION

Changes or modifications not expressly approved by the
manufacturer could void the user’s authority to operate this
equipment.

!

WARRANTY/DISCLAIMER

MEGA ENGINEERING, INC. warrants this unit to be free of defects in materials and

orkmanship for a period of 37 months from date of purchase. OMEGA Warranty adds an
dditional one (1) month grace period to the normal three (3) years product warranty to
over handling and shipping time. This ensures that OMEGA’s customers receive maximum
overage on each product.

the unit should malfunction, it must be returned to the factory for evaluation. OMEGA’s
ustomer Service Department will issue an Authorized Return (AR) number immediately upon
hone or written request. Upon examination by OMEGA, if the unit is found to be defective it will
e repaired or replaced at no charge. OMEGA’s WARRANTY does not apply to defects resulting

om any action of the purchaser, including but not limited to mishandling, improper interfacing,

peration outside of design limits, improper repair, or unauthorized modification. This

WARRANTY is VOID if the unit shows evidence of having been tampered with or shows evidence

f being damaged as a result of excessive corrosion; or current, heat, moisture or vibration;

mproper specification; misapplication; misuse or other operating conditions outside of OMEGA’s

ontrol. Components which wear are not warranted, including but not limited to
ontact points, fuses, and triacs.

MEGA is pleased to offer suggestions on the use of its various products. However,

MEGA neither assumes responsibility for any omissions or errors nor assumes liability for
ny damages that result from the use of its products in accordance with information pro­ided by OMEGA, either verbal or written. OMEGA warrants only that the parts

manufactured by it will be as specified and free of defects. OMEGA MAKES NO OTHER
WARRANTIES OR REPRESENTATIONS OF ANY KIND WHATSOEVER, EXPRESSED OR

MPLIED, EXCEPT THAT OF TITLE, AND ALL IMPLIED W ARRANTIES INCLUDING ANY WAR-

ANTY OF MERCHANTABILITY AND FITNESS FOR A P AR TICULAR PURPOSE ARE HEREBY

ISCLAIMED. LIMITATION OF LIABILITY: The remedies of purchaser set forth herein are
xclusive and the total liability of OMEGA with respect to this order, whether based on con-

ract, warranty, negligence, indemnification, strict liability or otherwise, shall not exceed
he purchase price of the component upon which liability is based. In no event shall OMEGA

e liable for consequential, incidental or special damages.

ONDITIONS: Equipment sold by OMEGA is not intended to be used, nor shall it be used: (1) as

“Basic Component” under 10 CFR 21 (NRC), used in or with any nuclear installation or activity;

r (2) in medical applications or used on humans. Should any Product(s) be used in or with any
uclear installation or activity, medical application, used on humans, or misused in any way,

MEGA assumes no responsibility as set forth in our basic WARRANTY/DISCLAIMER language,

nd additionally, purchaser will indemnify OMEGA and hold OMEGA harmless from any liability

r damage whatsoever arising out of the use of the Product(s) in such a manner .

RETURN REQUESTS / INQUIRIES

irect all warranty and repair requests/inquiries to the OMEGA Customer Service Department.
EFORE RETURNING ANY PRODUCT(S) TO OMEGA, PURCHASER MUST OBTAIN AN
UTHORIZED RETURN (AR) NUMBER FROM OMEGA’S CUSTOMER SERVICE DEPARTMENT

N ORDER TO AVOID PROCESSING DELAYS). The assigned AR number should then be

marked on the outside of the return package and on any correspondence.

he purchaser is responsible for shipping charges, freight, insurance and proper packaging to
revent breakage in transit.

OR W

ARRANTY RETURNS, please have

he following information available BEFORE

ontacting OMEGA:

. P.O. number under which the product was

PURCHASED,

. Model and serial number of the product

under warranty, and

. Repair instructions and/or specific

problems relative to the product.

FOR NON-WARRANTY REPAIRS,

consult
OMEGA for current repair charges. Have the
following information available BEFORE
contacting OMEGA:

1. P.O. number to cover the COST

of the repair,

2. Model and serial number of product, and

3. Repair instructions and/or specific problems

relative to the product.

MEGA’s policy is to make running changes, not model changes, whenever an improvement is possible.

his affords our customers the latest in technology and engineering.

MEGA is a registered trademark of OMEGA ENGINEERING, INC.

Copyright 1996 OMEGA ENGINEERING, INC. All rights reserved. This document may not be copied, photocopied,

produced, translated, or reduced to any electronic medium or machine-readable form, in whole or in part, without

ior written consent of OMEGA ENGINEERING, INC.

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M2831/0298