TechPro
™
Operation
Manual
Model ARH1
MYRON L
COMPANY
10-02 (WEB) EG
Instrument Illustration
METER
pH/CONDUCTIVITY
Reference
Junction
(under Glass
Bulb)
pH Sensor
(User replaceable)
Conductivity Cell
(Built-in
Electrodes)
Temperature
Sensor
User selectable
temperature
compensation
ratios (Solution
Selection)
Icon for pH
LO BATT
KCl
NaCl
442
COND
TDS
pH/CONDUCTIVITY
mS
µS
PPM
PPT
°C
pH
TDSCOND
pH
pH Glass
Electrode
pH Sensor
Protective Cap
Units of Measurement
mS - millisiemens/cm
(millimhos/cm)
µS - microsiemens/cm
(micromhos/cm)
PPM - parts per million
PPT - parts per thousand
Icons for either
Conductivity or
Total Dissolved
Solids (TDS)
pH key
Conductivity or TDS key:
User selectable for either
Conductivity or TDS
(Switch Selectable)
Parameter
Conductivity
Conductivity
TDS
TDS
ARH1
MYRON L
COMPANY
For detailed explanations, see Table of Contents
Wrist/neck strap slot
(user supplied)
1-12-99
1
FEATURES and SPECIFICATIONS
A. Features
• Superior resolution 3 1/2 digit LCD
• Conductivity/TDS accuracy of ±1% of full scale
• pH accuracy of ± .05 pH units
• All electrodes are internal for maximum protection
• Latest electrode cell technology
• Water resistant
• Autoranging Conductivity/TDS
• Easy Conductivity/TDS and pH calibration
• User selectable Conductivity/TDS modes
• 3 “User Selectable” solution conversions (tempcos)
• Temperature Accuracy of ±1° C/F
B. General Specifications
Display 3 1/2 Digit LCD
Dimensions (LxWxH) 7.7x2.7x2.5 in.
196x68x64 mm
Weight 11.2oz./320g
Case Material ABS
Cond/TDS Cell Material ABS
Cond/TDS Cell Capacity 0.2 oz./5 ml
pH Sensor Well Capacity 0.04 oz./1.2 ml
Power 9V Alkaline Battery
Battery Life >100 Hours/5000 Readings
Operating/Storage Temperature 32-132°F/0-55°C
Protection Ratings IP64/NEMA 3
C. Specification Chart
D. Warranty/Service
The ARH1 has a 2 year warranty, excluding the pH sensor, which has
limited 6 month warranty. If an instrument fails to operate properly, see the
Troubleshooting Chart, pg. 17. The battery and pH sensor are user-replaceable
For other service, return the instrument prepaid to the Myron L Company.
MYRON L COMPANY
2450 Impala Drive
Carlsbad, CA 92010
USA
760-438-2021
If, in the opinion of the factory, failure was due to materials or
workmanship, repair or replacement will be made without charge. A
reasonable service charge will be made for diagnosis or repairs due to
normal wear, abuse or tampering. This warranty is limited to the repair or
replacement of the ARH1 only. The Myron L Company assumes no other
responsibility or liability.
E. TechPro™ Series Models
TechPro Series Models pH1 AR1 ARH1
Parameters pH Conductivity or TDS, Conductivity or TDS,
& Temperature & Temperature pH & Temperature
Additional information available on our web site at:
www.myronl.com
ARH1 p H Conductivity TDS Temperature
Ranges 0-14 pH 0-1999 µS 0-1999 ppm 0-71° C
2-19.90 mS 2-19.90 ppt 32 - 16 0° F
in 3 autoranges in 3 autoranges
Resolution .01 pH 0.1 (<200 µS) 0.1 (<200 ppm) 0.1° C/F
1 (<2000 µS) 1 (<2000 ppm)
0.01 (>2 mS) 0.01 (>2 ppt)
Accuracy ±.05 pH ±1% of Full Scale ±1.0° C/F
Auto Temperature 0-71° C 0-71° C
Compensation 32 - 160° F 32 - 160° F
Conductivity or KCl, NaCl or 442™
TDS Ratios
2 3
TABLE OF CONTENTS
Instrument Illustration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
FEATURES and SPECIFICATIONS. . . . . . . . . . . . . . . . . . . . . . . . . 2
A. Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
B. General Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . 2
C. Specification Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
D. Warranty/Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
E. TechPro Series Models . . . . . . . . . . . . . . . . . . . . . . . . .3
I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
II . RULES of OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
A. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
B. Characteristics of the Keys . . . . . . . . . . . . . . . . . . . . . . 6
C. Operation of the Keys . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Measurement Keys in General . . . . . . . . . . . . 6
2. COND/TDS Key. . . . . . . . . . . . . . . . . . . . . . . . .7
3. pH Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
III. AFTER USING the ARH1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
A. Maintenance of the Conductivity Cell . . . . . . . . . . . . . 7
B. Maintenance of the pH Sensor. . . . . . . . . . . . . . . . . . . 7
IV. THE SPECIFIC RECOMMENDED MEASURING
PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
A. Measuring Conductivity/Total Dissolved Solids . . . . .8
B. Measuring pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
VII. CALIBRATION INTERVALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
A. Suggested Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . .13
B. Calibration Tracking Records . . . . . . . . . . . . . . . . . . . 13
C. Conductivity or TDS Practices . . . . . . . . . . . . . . . . . . 13
D. pH Practices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
VIII. CHANGING from CENTIGRADE to FAHRENHEIT. . . . . . . . . . . . 14
IX. CARE and MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
A. Temperature Extremes . . . . . . . . . . . . . . . . . . . . . . . . 14
B. Battery Replacement (LO BATT) . . . . . . . . . . . . . . . . 14
C. pH Sensor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
D. Cleaning Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
X. TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
XI. ACCESSORIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
A. Conductivity/TDS Standard Solutions . . . . . . . . . . . 18
B. pH Buffer Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
C. pH Sensor Storage Solution . . . . . . . . . . . . . . . . . . . .18
D. Soft Protective Case . . . . . . . . . . . . . . . . . . . . . . . . . . 18
E. Replacement pH Sensor. . . . . . . . . . . . . . . . . . . . . . . 19
XII. TEMPERATURE COMPENSATION . . . . . . . . . . . . . . . . . . . . . . . 19
A. Standardized to 25°C . . . . . . . . . . . . . . . . . . . . . . . . . .19
B. Tempco Variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
C. An Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
D. A Chart of Comparative Error . . . . . . . . . . . . . . . . . . . .20
E. Other Solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
V. SOLUTION SELECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
A. Why Solution Selection is Available . . . . . . . . . . . . . . .8
B. The 3 Solution Types . . . . . . . . . . . . . . . . . . . . . . . . . . .8
C. Procedure to Select a Solution . . . . . . . . . . . . . . . . . . 9
D. Procedure to Select the Units of Measurement . . . . .9
VI. CALIBRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
A. Calibration Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
B. Rules for Calibration of the ARH1 . . . . . . . . . . . . . . . .10
1. Calibration Steps . . . . . . . . . . . . . . . . . . . . . . .10
2. Calibration Limits . . . . . . . . . . . . . . . . . . . . . . .10
C. Calibration Procedures. . . . . . . . . . . . . . . . . . . . . . . . .10
1. Conductivity or TDS Calibration. . . . . . . . . . .10
2. pH Calibration . . . . . . . . . . . . . . . . . . . . . . . . . 11
4 5
XIII. CONDUCTIVITY CONVERSION to TOTAL DISSOLVED SOLIDS
(TDS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
A. How it’s Done . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
B. Solution Characteristics . . . . . . . . . . . . . . . . . . . . . . . .21
C. When does it make a lot of difference? . . . . . . . . . . . 22
XIV. TEMPERATURE COMPENSATION (Tempco)
and TDS DERIVATION. . . . . . . . . . . . . . . . . . . . . . . . . . . .22
XV. pH MEASURING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
XVI. GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
NOTES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 27
I. INTRODUCTION
Thank you for selecting the TechPro™ Series, Model ARH1, one of the
Myron L Company’s latest in a new line of digital instruments utilizing
advanced circuitry. This circuitry makes it very accurate and easy to use
(see pages 2 & 3 for Features and Specifications on this and other
models). For your convenience, on the bottom side of your ARH1 is a
brief set of instructions.
Special note ...... Conductivity/TDS require mathematical correction to
25°C values (ref. Temperature Compensation, pg. 19).
On the left side of the ARH1 liquid crystal display is shown an indicator of
the salt solution characteristic used to model temperature compensation
(Tempco) of conductivity or its TDS conversion. The indicator can be KCl,
NaCl or 442. Internal selection affects the temperature correction of
conductivity, and the calculation of TDS from compensated conductivity
(ref. Conductivity Conversion to TDS, pg. 21).
The selection can affect the reported conductivity of hot or cold
solutions, and will change the reported TDS of a solution. Generally,
using KCl for conductivity and 442™ (Natural Water characteristic) for TDS
will reflect present industry practice for standardization. NaCl may also be
selected for either conductivity or TDS as is needed.
Your instrument, as shipped from the factory, is set for conductivity with
the KCl tempco. However, if you are measuring natural waters and wish to
have maximum accuracy, you may want to change it to the 442 tempco
setting. To change the Tempco or to read in TDS/ppm, see Solution
Selection on pg. 8.
The mode is shown at the bottom of the display, and the measurement
units appear at the right.
2. COND/TDS Key
This key is used with solution in the Conductivity Cell.
Precautions:
• While filling cell cup ensure no air bubbles cling on the cell wall.
• If the proper solution is not selected (KCl, NaCl or 442), refer to
Solution Selection on pg. 8.
Solution to be tested is introduced into the conductivity cell and a press
COND
of displays conductivity or Total Dissolved Solids (TDS) with units
TDS
on the right. On the left is shown the solution type selected for
conductivity. An overrange condition will show only [- - - -].
3. pH Key
Measurements are made on the solution held in the pH sensor well (ref.
pH Measuring, pg. 23). The protective cap is removed, and the sensor
well is filled and rinsed with sample enough times to completely replace
the storage solution. After use, the pH sensor well must be refilled with
Myron L Storage Solution, and the protective cap reinstalled securely
(ref. Maintenance of the pH Sensor, below, and pH, pg. 15).
A press of displays pH readings. No units are displayed.
pH
II. RULES of OPERATION
A. Operation
Using the instrument is simple:
• Individual or dual parameter readings may be obtained by filling
individual sensors or entire cell cup area.
• Rinse the Conductivity cell or pH sensor well with test solution 3
times and Refill.
III. AFTER USING the ARH1
A. Maintenance of the Conductivity Cell
Rinse out the cell cup with clean water. Do not scrub the cell. For oily
films, squirt in a foaming non-abrasive cleaner and rinse. Even if a very
active chemical discolors the electrodes, this does not affect the
accuracy; leave it alone (ref. Conductivity or TDS, pg. 15).
• Pressing either measurement key starts a 20 second timer.
• Note the value displayed. It’s that simple!
B. Maintenance of the pH Sensor
The sensor well must be kept wet with a solution. Before replacing the
B. Characteristics of the Keys
• Your ARH1 is designed to provide quick, easy, accurate
measurements by simply pressing one key.
• Both functions are performed one key at a time.
C. Operation of the Keys (See Instrument Illustration on page 1)
1. Measurement Keys in General
The measurement keys turn on the instrument in the mode selected.
rubber cap, rinse and fill the sensor well with (in order of preference):
Myron L Storage Solution, an almost saturated KCl solution, pH 4 buffer
(ref. pH Buffer Solutions, pg. 18) or at least a strong table salt solution.
Not distilled water (ref. pH, pg. 15).
IV. THE SPECIFIC RECOMMENDED MEASURING
PROCEDURES
If the proper solution is not selected (KCl, NaCl or 442), see Solution
Selection, Pg. 8.
6 7
NOTE: After sampling high concentration solutions or temperature
extremes, more rinsing may be required. When sampling low conductivity
solutions, be sure the pH cap is well seated so no solution washes into
the conductivity cell from around the pH cap.
A. Measuring Conductivity/Total Dissolved Solids (TDS)
1. Rinse cell cup 3 times with sample to be measured. (This
conditions the temperature compensation network and prepares
the cell).
model temperature compensation of conductivity and its TDS
conversion. Generally, using KCl for conductivity and 442 (Natural Water
characteristic) for TDS will reflect present industry practice for
standardization. Your instrument as shipped from the factory is set for
conductivity with the KCl tempco. If you are measuring natural waters and
wish to have maximum accuracy, it may be better to change it to the 442
setting. However, selecting NaCl for either conductivity or TDS may best
reflect your specific specialized needs (ref. Solution Characteristics, pg.
21). NOTE: Before opening instrument, Dry THOROUGHLY.
2. Refill cell cup with sample.
3. Press .
COND
TDS
NOTE: Check display to see if solution displayed (KCl, NaCl or 442) is
already the type desired. If not:
C. Procedure to Select a Solution
4. Take reading. A display of [- - - -] indicates an overrange
condition.
B. Measuring pH
1. Remove the 4 bottom screws and carefully open Instrument.
2. Locate dip switch labeled “TEMP COMP” on the right side of the
circuit board. Switch positions are 1-4 (left to right).
1. Remove protective cap by squeezing its sides and pulling up.
3. Set switch numbers 1 and 2 to the desired position.
2. Rinse sensor well 3 times with sample to be measured. Shake
out each sample to remove any residual liquid.
4. Carefully turn instrument over and press the key. The
3. Refill sensor well with sample.
Note: Factory setting is for KCl - both switches UP or ON.
COND
TDS
correct icon “KCl”, NaCl” or “442” should be shown on the left
4. Press .
pH
5. Take reading.
5. Replace bottom, ensuring the sealing gasket is installed in the groove
side of the display.
of the top half of case. Tighten screws securely. (Do NOT overtighten)
6. IMPORTANT: After use, fill pH sensor well with Myron L
Storage Solution, a strong KCl solution or pH 4 buffer, and
6. Recalibrate as necessary. See Calibration, pg. 10.
replace protective cap. Do not allow pH sensor to dry out.
D. Procedure to Select the Units of Measurement
NOTE: If a storage solution, KCl or pH 4 solution is unavailable, use a
i.e. µS to ppm
saturated solution of table salt and water (ref. pH, pg. 15).
1. Remove the 4 bottom screws and open Instrument.
V. SOLUTION SELECTION
A. Why Solution Selection is Available
Conductivity and TDS require temperature correction to 25°C values (ref.
2. Locate dip switch labeled “TEMP COMP” located on the right
side of the circuit board. Switch positions are 1-4 (left to right).
Standardized to 25°C, pg. 19). Selection determines the temperature
correction of conductivity and calculation of TDS from compensated
conductivity (ref. Conductivity Conversion to TDS, pg. 21).
B. The 3 Solution Types
On the left side of the display is the salt solution characteristic used to
8 9
3. Set switch number 3 to the desired position - COND or TDS.
Note: Factory setting is for COND - DOWN or OFF.
4. Carefully turn instrument over and press the key. The
COND
TDS
correct icon, “µS” or “ppm”, should be shown on the right side of
the display.
5. Replace bottom, ensuring the sealing gasket is installed in the groove
of the top half of case. Tighten screws securely. (Do NOT overtighten)
d. Remove cap plug labeled COND CAL on bottom of Instrument.
e. Refill conductivity cell with same standard solution.
f. While pressing the key, adjust COND CAL Control with
COND
TDS
6. Recalibrate as necessary. See Calibration, below.
finger until the display agrees with the value on the standard
solution bottle.
In the first five sections, you have learned all
you need to make accurate measurements.
The following sections contain calibration,
advanced operations, and technical information.
VI. CALIBRATION
g. Repeat steps b. & c. to verify the setting.
h. Replace bottom cap plug securely to maintain water resistance.
The COND/TDS Calibration procedure is now complete.
2. pH Calibration
A. Calibration Intervals
Generally, calibration is recommended about once per month with
Conductivity or TDS solutions. Calibration with pH solutions should be
IMPORTANT: Always “zero” your ARH1 with a pH 7 buffer solution
before adjusting the gain with acid or base buffers, i.e., 4 and/or 10, etc.
checked twice a month.
a. pH Zero Calibration
B. Rules for Calibration of the ARH1
1. Calibration Steps
1. Remove protective cap.
Each calibration is accomplished by a Calibration Control located under
the respective cap plug on the bottom of the instrument.
2. Rinse sensor well 3 times with 7 buffer solution.
After pressing the respective key, the reading is changed/adjusted to
match the known standard or buffer value.
3. Refill sensor well with 7 buffer solution.
Depending on what is being calibrated, there may be 1, 2 or 3 steps to
the calibration procedures.
2. Calibration Limits
In Conductivity or TDS, the inability to calibrate may indicate improper or
4. Press to verify the pH calibration. If the display reads 7.00,
pH
skip the pH Zero Calibration and proceed to section b. pH Gain
Calibration. If reading is not acceptable, continue.
contaminated calibration solution, or a damaged conductivity cell.
In pH, the inability to calibrate may indicate improper or contaminated
5. Remove cap plug labeled ZERO CAL on bottom of Instrument.
buffer solution or a damaged pH Sensor.
NOTE: If the pH reading displayed will not adjust to the proper reading,
C. Calibration Procedures
1. Conductivity /TDS Calibration
a. Rinse conductivity cell three times with proper standard (KCl,
the sensor well needs additional rinsing or fresh buffer solution, or the pH
sensor is bad and needs to be replaced (ref. Troubleshooting Chart, pg.
17).
NaCl or 442) (ref. Conductivity/TDS Standard Solutions, pg. 18).
6. Refill sensor well again with 7 buffer solution.
b. Refill conductivity cell with same standard solution.
c. Press key. If reading is acceptable, end procedure. If
COND
TDS
7. While pressing the key, adjust ZERO CAL Control with
finger until the display reads 7.00.
pH
reading is unacceptable, continue.
10 11
8. Replace bottom cap plug securely to maintain water resistance.
The pH ZERO Calibration procedure is now complete. You may continue
with pH Gain Calibration or stop and replace storage solution & pH cap.
The most common sources of error were eliminated in the design, and
there are simple electromechanical adjustments. Still, to ensure specified
accuracy, any instrument has to be checked against chemical standards
occasionally.
b. pH Gain Calibration
IMPORTANT: Always calibrate or verify your ARH1 with a pH 7 buffer
solution before adjusting the gain with acid or base buffers, i.e., 4 and/or
10, etc. The pH gain calibration is performed in the same manner as the
ZERO. For maximum accuracy use a buffer value closest to instrument’s
normal area of use, i.e., if you normally measure acidic solutions, use “4”
buffer.
1. Rinse the sensor well 3 times with acid or base buffer solution.
2. Refill sensor well again with same buffer solution.
3. Press key. If reading is acceptable, end procedure. If
not, continue.
4. Remove cap plug labeled GAIN CAL on bottom of Instrument.
5. Refill sensor well again with same buffer solution.
6. While pressing the , adjust GAIN CAL Control with
finger until reading agrees with buffer solution.
7. If the instrument will be used to read both acids and bases,
repeat steps 1 and 6 using opposite buffer solution.
8. If reading is different by more than is acceptable, split the
difference with the previous setting. (If it is not possible to
adjust Gain, it is an indication of bad buffers or a deteriorating
or damaged pH sensor.)
9. Replace bottom cap plug securely to maintain water resistance.
The pH GAIN Calibration procedure is now complete.
pH
pH
A. Suggested Intervals
On the average, we expect calibration need only be checked monthly for
the Conductivity or TDS functions. The pH function should be checked
every 2 weeks to ensure accuracy. Measuring some solutions will require
more frequent intervals.
B. Calibration Tracking Records
To minimize your calibration effort, keep records. If adjustments you are
making are minimal for your application, you can check less often.
Changes in conductivity calibration should be recorded in percent.
Changes in pH calibration are best recorded in pH units.
Calibration is purposely limited in the ARH1 to ±8% for the conductivity
cell because more than that indicates damage, not drift. Likewise, pH
calibration changes are limited to ±1 pH unit because more than that
indicates the end of the sensor lifetime, and it should be replaced.
C. Conductivity or TDS Practices to Maintain Calibration
1. Clean oily films or organic material from the cell electrodes with
foaming cleaner or mild acid. Do not scrub inside the cell.
2. Calibrate with solutions close to the measurements you make.
Readings are compensated for temperature based on the
type of solution. If you choose to measure tap water with a
KCl compensation, which is often done (ref. Temperature
Compensation, pg. 19), and you calibrate with 442 solution
because it is handy, the further away from 25°C you are, the
more error you have. Your records of calibration changes
will reflect temperature changes more than the instrument’s
accuracy.
3. Rinse out the cell with pure water after making measurements.
Allowing slow dissolving crystals to form in the cell contaminates
future samples.
VII. CALIBRATION INTERVALS
There is no simple answer as to how often one should calibrate an
instrument. The ARH1 is designed to not require frequent recalibration.
12 13
4. For maximum accuracy, keep the pH cell cover on tight so no fluid
washes into the conductivity cell.
D. pH Practices to Maintain Calibration.
and securely. (Do NOT overtighten)
1. Keep the sensor wet with Myron L Storage Solution.
Order model RPG. When ordering, be sure to include the model and
2. Rinse away caustic solutions immediately after use.
VIII. CHANGING from CENTIGRADE to FAHRENHEIT
(Note: °F to °C is the reverse)
1. Dry Instrument THOROUGHLY.
2. Remove the 4 bottom screws and carefully open Instrument.
3. Locate dip switch labeled “TEMP COMP” on the right side of the
circuit board. Note: Factory setting is degrees “C”.
4. Set switch number 4 to the down position.
5. Carefully turn instrument over and press the key. The
displayed reading will be in Fahrenheit “°F”.
6. Replace bottom, ensuring the sealing gasket is installed in the groove
of the top half of case. Tighten screws securely. (Do NOT overtighten)
IX. CARE and MAINTENANCE
The ARH1 should be rinsed with clean water after each use. Solvents
should be avoided. Shock damage from a fall may cause instrument
failure.
A. Temperature Extremes
Solutions in excess of 160°F/71°C should not be placed in the cell cup
area; this may cause damage. The pH sensor may fracture if the ARH1
temperature is allowed to go below -10°C (14°F). Care should be
exercised not to exceed rated operating temperature. Leaving the ARH1
in a vehicle or storage shed on a hot day can easily subject the instrument
to over 150°F. This will void the warranty.
B. Battery Replacement (LO BATT)
Dry Instrument THOROUGHLY. Remove the 4 bottom screws.
Open instrument. Carefully detach battery from circuit board. Replace
with 9 volt alkaline battery. Replace bottom, ensuring the sealing gasket
is installed in the groove of the top half of case. Tighten screws evenly
14 15
pH
serial number of your instrument to ensure receiving the proper type.
Complete installation instructions are provided with each replacement
sensor.
The cell cup should be kept as clean as possible. Flushing with clean
water following use will prevent buildup on electrodes. However, if very
dirty samples — particularly scaling types — are allowed to dry in the cell
cup, a film will form. This film reduces accuracy. When there are visible
films of oil, dirt, or scale in the cell cup or on the electrodes, use a foaming
non-abrasive household cleaner. Rinse out the cleaner, and your ARH1
is ready for accurate measurements.
The unique pH sensor in your ARH1 is a nonrefillable combination type
which features a porous liquid junction. It should not be allowed to dry
out. If it does, the sensor can sometimes be rejuvenated by first cleaning
the sensor well with a liquid spray cleaner such as Windex™ or Fantastic™
and rinsing well. Do not scrub or wipe the pH sensor.
Then use one of the following methods:
1. Pour a HOT salt solution ~60°C (140°F), preferably potassium
Or
2. Pour DI water in the sensor well and allow to stand for no more
If neither method is successful, sensor must be replaced.
"Drifting" can be caused by a film on the pH sensor bulb. Spray a liquid
cleaner such as Windex™ or Fantastic™ into the sensor well to clean it.
The sensor bulb is very thin and delicate. Do not scrub or wipe the pH
sensor.
Leaving high pH (alkaline) solutions in contact with the pH sensor for long
periods of time can damage it. Rinsing such liquids from the pH sensor
well and refilling well with Myron L Storage Solution, a saturated KCl
solution, pH 4 buffer, or a salty tap water, will extend the useful life.
C. pH Sensor Replacement
D. Cleaning Sensors
1. Conductivity or TDS
2. pH
chloride (KCI) solution — HOT tap water with table salt (NaCl)
will work fine — in the sensor well and allow to cool. Retest.
than 4 hours (longer can deplete the reference solution and
damage the glass bulb). Retest.
pH Sensor
Top View
Sensor
Body
Samples containing chlorine, sulfur, or ammonia can "poison" any pH
electrode. If it is necessary to measure the pH of any such sample,
thoroughly rinse the pH sensor well with clean water immediately after
taking the measurement. Any sample element which will reduce (add an
electron to) silver, such as cyanide, will attack the reference electrode.
Replacement pH sensors are available only from the Myron L Company or
our authorized distributors.
pH Glass
Electrode
Reference
Junction
under Glass
pH Bulb
16
X. TROUBLESHOOTING CHART
Symptom Possible Cause Corrective Action
No display, even though Battery weak or not connected. Check connections or replace battery
measurement key pressed. (ref. Battery Replacement, pg. 14).
Inaccurate pH readings 1. pH calibration needed (ref. pH Cal., pg. 11). 1. Recalibrate instrument.
2. Cross-contamination from residual 2. Thoroughly rinse sensor well.
pH buffers or samples in sensor well. 3. Recalibrate using fresh buffers (ref.
3. Calibration with expired pH buffers. pH Buffer Solution, pg. 18).
No response to pH changes Sensor bulb is cracked or an electro- Replace pH sensor (ref. pH Sensor, pg. 15).
mechanical short caused by an internal crack.
Will not adjust down to pH 7. pH sensor has lost KCl. Clean and rejuvenate sensor (ref. pH, pg. 15)
and recalibrate. If no improvement, replace
pH sensor (ref. pH Sensor Replacement, pg.
15).
pH readings drift or respond 1. Temporary condition due to “memory” of Clean and rejuvenate sensor (ref. pH, pg. 15)
slowly to changes in solution in pH sensor well for long periods. and recalibrate. If no improvement, replace
buffers/samples. 2. Bulb dirty or dried out. pH sensor (ref. pH Sensor Replacement, pg.
3. Reference junction clogged or coated. 15).
Unstable Conductivity or Film or deposits on electrodes. Clean cell cup and electrodes
TDS readings. (ref. Conductivity or TDS, pg. 15).
Unable to calibrate Film or deposits on electrodes. Clean cell cup and electrodes (ref.
Conductivity or TDS. Conductivity or TDS, pg. 15).
17
XI. ACCESSORIES
A. Conductivity/TDS Standard Solutions
Your ARH1 has been factory calibrated with the appropriate Myron L
Company NIST traceable standard solution. Most Myron L conductivity
standard solution bottles show three values referenced at 25°C:
Conductivity in microsiemens/micromhos and the ppm/TDS equivalents
based on our 442 Natural Water™ and NaCl standards. All standards are
within ±1.0% of reference solutions.
1. Potassium Chloride (KCl)
The concentrations of these reference solutions are calculated from data
in the International Critical Tables, Vol. 6. The 1800 µS or 18,000 µS are
the recommended standards. Order KCl-1800 or KCl-18,000.
2. 442 Natural Water™
442 Natural Water Standard Solutions are based on the following salt
proportions: 40% sodium sulfate, 40% sodium bicarbonate, and 20%
sodium chloride which represent the three predominant components
“anions” in freshwater. This salt ratio has conductivity characteristics
approximating fresh natural waters and was developed by the Myron L
Company over three decades ago. It is used around the world for
measuring both conductivity and TDS in drinking water, ground water,
lakes, streams, etc. The 1500 ppm or 15,000 ppm are the recommended
standards. Order 442-1500 or 442-15,000.
3. Sodium Chloride (NaCl)
This is especially useful in sea water mix applications, as sodium chloride
is its major salt component. Most Myron L standard solution labels show
the ppm NaCl equivalent to the conductivity and to ppm 442 values. The
14.0 mS is the recommended standard. Order NaCl-14.0.
E. Replacement pH Sensor
Model RPG is gel filled and features a unique porous liquid junction. It is
user-replaceable and comes with easy to follow instructions.
XII. TEMPERATURE COMPENSATION
(Tempco) of Aqueous Solutions
Electrical conductivity indicates solution concentration and ionization of
the dissolved material. Since temperature greatly affects ionization,
conductivity measurements are temperature dependent and are normally
corrected to read what they would be at 25°C.
A. Standardized to 25°C
Conductivity is very accurately measured in the ARH1 by a method that
ignores fill level, electrolysis, electrode characteristics, etc., and uses a
unique circuit to perform temperature compensation. In simpler
instruments, conductivity values are usually assigned an average
correction similar to KCl solutions for correction to 25°C. The correction to
an equivalent KCl solution is a standard set by chemists. It standardizes
the measurements and allows calibration with precise KCl solutions,
recognized for stability. In the ARH1, this correction can be set to either
KCl, NaCl or 442 to best match your applications.
B. Tempco Variation
Most conductivity instruments use an approximation of the temperature
characteristics of solutions, perhaps even assuming a constant value.
The value for KCl is often quoted simply as 2%/°C. In fact, KCl tempco
2.500%
2.400%
2.300%
B. pH Buffer Solutions
pH buffers are available in pH values of 4, 7 and 10. Myron L Company
buffer solutions are traceable to NIST certified pH references and are
color-coded for instant identification. They are also mold inhibited and
accurate to within ±0.01 pH units @ 25°C. Order 4, 7 or 10 buffer.
C. pH Sensor Storage Solution
Myron L Storage Solution prolongs the life of the pH sensor. It is available
2.200%
2.100%
2.000%
1.900%
1.800%
1.700%
% / °C
KCl % / °C
in quarts and gallons. Order SSQ or SSG.
1.600%
D. Soft Protective Case
Padded Cordura® Nylon carrying case features a belt clip for hands-free
mobility. Order Model: UCC ® Registered trade mark of DuPont
1.500%
0 5 10 15 20 25 30 35 40 45 50 55 60
Temperature
Chart 1
18 19
varies with concentration and temperature in a non-linear fashion. Other
solutions have more variation still. The ARH1 uses corrections that
change with concentration and temperature instead of single average
values (see Chart 1, pg. 19).
C. An Example of 2 different solution selections and the
resulting compensation:
How much error results from treating natural water as if it were KCl at
15°C?
A tap water solution should be compensated as 442 with a tempco of
1.68 %/°C, where the KCl value used would be 1.90 %/°C.
Suppose a measurement at 15°C (or 59°F) is 900 microsiemens of true
uncompensated conductivity.
Using a 442 correction of 10 (degrees below 25) x 1.68% indicates the
solution is reading 16.8% low. For correction, dividing by (.832) yields
1082 microsiemens as a compensated reading.
A KCl correction of 10 (degrees below 25) x 1.9% indicates the solution
is reading 19% low. Dividing by (.81) yields 1111 microsiemens for a
compensated reading. The difference is 29 out of 1082 = 2.7%.
D. A Chart of Comparative Error
In the range of 1000 µS, the error using KCl on a solution that should be
compensated as NaCl or as 442, is shown in the graph below.
7%
442 error with KCl tempco
6%
Users wanting to measure natural water based solutions to 1% would
have to alter the internal compensation to the more suitable preloaded
“442” values or stay close to 25°C. Some who have standardized to KCl
based compensation may want to stick with it, regardless of increasing
error as you get further from 25°C. The ARH1 will provide the repeatability
and convertibility of data needed for relative values for process control.
E. Other Solutions
A salt solution like sea water or liquid fertilizer acts like NaCl. An internal
correction for NaCl can be selected for greatest accuracy with such
solutions. Many solutions are not at all similar to KCl, NaCl or 442. A sugar
solution, or a silicate, or a calcium salt at a high or low temperature may
require a value peculiar to the application to provide readings close to the
true compensated conductivity.
Clearly, the solution characteristics should be chosen to truly represent
the actual water under test for rated accuracy of ±1% of full scale. Many
industrial applications have always been relative measurements seeking a
number to indicate a certain setpoint or minimum concentration or trend.
The ARH1 gives the user the capability to take data in “KCl conductivity
units” to compare to older published data, as in terms of NaCl or 442, or
as may be appropriate.
XIII. CONDUCTIVITY CONVERSION to TOTAL
DISSOLVED SOLIDS (TDS)
Electrical conductivity indicates solution concentration and ionization of
the dissolved material. Since temperature greatly affects ionization,
conductivity measurements are temperature dependent and are normally
corrected to read what they would be at 25°C (ref. Temperature
Compensation, pg. 19).
NaCl error with KCl tempco
5%
4%
3%
2%
1%
Once the effect of temperature is removed, the compensated
conductivity is a function of the concentration (TDS). Temperature
compensation of the conductivity of a solution is performed automatically
by the internal processor, using data derived from chemical tables. Any
dissolved salt at a known temperature has a known ratio of conductivity to
concentration. Tables of conversion ratios referenced to 25°C have been
published by chemists for decades.
A. How it’s Done
0%
(1)%
Temperature
(2)%
0 5 10 15 20 25 30 35 40 45 50 55
20 21
Chart 2
Real world applications have to measure a wide range of materials and
mixtures of electrolyte solutions. To solve this problem, industrial users
commonly use the characteristics of a standard material as a model for
B. Solution Characteristics
their solution, like the KCl favored by chemists for its stability.
Users dealing with sea water, etc., use NaCl as the model for their
concentration calculations. Users dealing with freshwater work with
mixtures including sulfates, carbonates and chlorides, the three
predominant components (anions) in freshwater that Myron L Company
calls “natural water”. These are modeled in a mixture called “442” which
the Myron L Company markets for use as a calibration standard, as it does
standard KCl and NaCl solutions.
Another solution would have a different tempco because of its ionization
activity. And, that tempco may be a little different at a different
concentration or temperature. This is why the ARH1 uses mathematically
generated models for known salt characteristics that vary with
concentration and temperature.
The ARH1 contains circuitry for characteristics of the 3 most commonly
referenced compounds — KCl, NaCl and 442. In the display, the solution
type being used is shown on the left.
C. When does it make a lot of difference?
First, the accuracy of temperature compensation to 25°C determines the
accuracy of any TDS conversion. Assume we have industrial process
water to be pretreated by R.O. Assume it is 45°C and reads 1500 µS
uncompensated.
1. If NaCl compensation is used, an instrument would report 1035
µS compensated, which corresponds to 510 ppm NaCl.
2. If 442 compensation is used, an instrument would report 1024
µS compensated, which corresponds to 713 ppm 442.
The difference in values is 40%.
In spite of such large error, some users will continue to take data in the
NaCl mode because their previous data gathering and process
monitoring was done with an older NaCl referenced device.
Those who want true TDS readings that will correspond to evaporated
weight will select the correct Solution Type.
The ARH1 contains circuitry for the 3 most commonly referenced
compounds — KCl, NaCl and 442. In the LCD display, the solution type
being used is shown on the left.
XIV. TEMPERATURE COMPENSATION (Tempco)
and TDS DERIVATION
When making conductivity measurements, the Solution Selection
determines the characteristic assumed as the instrument reports what a
measured conductivity would be if it were at 25°C. The characteristic is
represented by the tempco, expressed in %/°C. If a solution of 100 µS at
25°C increases to 122 µS at 35°C, then a 22% increase has happened
over this change of 10°C. The solution is said to have a tempco of 2.2
%/°C.
22 23
XV. pH MEASURING
A. pH as an Indicator
pH is the measurement of Acidity or Alkalinity of an aqueous solution. It is
also stated as the Hydrogen Ion activity of a solution. pH measures the
effective, not the total, acidity of a solution.
A 4% solution of acetic acid (pH 4, vinegar) can be quite palatable, but a
4% solution of sulfuric acid (pH 0) is a violent poison. pH provides the
needed quantitative information by expressing the degree of activity of
an acid or base.
In a solution of one known component, pH will indicate concentration
indirectly. However, very dilute solutions may be very slow reading, just
because the very few ions take time to accumulate.
B. pH Units
The acidity or alkalinity of a solution is a measurement of the relative
availabilities of hydrogen (H ) and hydroxide (0H ) ions. An increase in
(H ) ions will increase acidity, while an increase in (OH ) ions will increase
alkalinity. The total concentration of ions is fixed as a characteristic of
water, and balance would be 10 mol/liter (H ) and (OH ) ions in a neutral
solution (where pH sensors give 0 voltage).
pH is defined as the negative logarithm of hydrogen ion concentration.
Where (H ) concentration falls below 10 , solutions are less acidic than
neutral, and therefore are alkaline. A concentration of 10 mol/liter of (H )
would have 100 times less (H ) ions than (OH ) ions and be called an
alkaline solution of pH 9.
The active part of the pH sensor is a thin glass surface which is selectively
receptive to hydrogen ions. Available hydrogen ions in a solution will
accumulate on this surface and a charge will build up across the glass
interface. The voltage can be measured with a very high impedance
+
C. The pH Sensor
+-
-+
-7 +-
-7
-9
+
-
+
voltmeter circuit; the trick is to connect the voltmeter to solution on each
side.
E. Sources of Error
The basics are presented in pH, pg. 15.
The glass surface encloses a captured solution of potassium chloride
holding an electrode of silver coated with silver chloride. This is as inert a
connection as can be made from metal to an electrolyte. It still can
produce an offset voltage, but using the same materials to connect to the
solution on the other side of the membrane allows the 2 equal offsets to
cancel.
The problem is... the other side of the
membrane is some test solution,
Glass surface
H+ ions
Junction plug
not potassium chloride. The
outside electrode, also called the
Reference Junction, is of the same
construction with a porous plug in
place of a glass barrier to allow the
junction fluid to contact the test
solution without significant
migration of liquids through the
plug material. The figure to the
right shows a typical 2 component
Electrode wire
KCl solution
Electrode wire
pair. Migration does occur, and this
limits the lifetime of a pH junction from depletion of solution inside the
reference junction or from contamination. The junction is damaged by
drying out because insoluble crystals may form in a layer, obstructing
contact with test solutions. See pH, pg. 15.
1. Reference Junction
The most common sensor problem will be a clogged junction because a
cell was allowed to dry out. The symptom is a drift in the “zero” setting at 7
pH. This is why the ARH1 does not allow more than 1 pH unit of offset
during calibration. At that point the junction is unreliable.
2. Sensitivity Problems
Sensitivity is the receptiveness of the glass surface, which can be
diminished by a film on the surface, or a crack in the glass. These
problems also cause long response time.
3. Temperature Compensation
pH sensor glass changes its sensitivity slightly with temperature, so the
further from pH 7 one is, the more effect will be seen. A pH of 11 at 40°C
would be off by 0.2 units. The ARH1 senses the cell temperature and
compensates the reading.
D. The Myron L Integral pH Sensor
The sensor in the ARH1 (figure at right)
is a single construction in an easily
Glass Surface
Junction plug
replaceable package. The sensor body
holds an oversize solution supply for
long life. The reference junction “wick”
KCl solution
is porous to provide a very stable, low
permeability interface. It is formed in a
ring around the pH sensing electrode.
The construction combines all the best
Glass
Sleeve
features of any pH sensor known.
Electrode wires
24 25
XVI. GLOSSARY
Anions - Negatively charged ions.
See Solution Characteristics, pg. 21.
Algorithm - A procedure for solving a mathematical problem.
See Temperature Compensation and TDS Derivation,
pg. 22.
Logarithm - An arithmetic function. See pH Units, pg. 23.
TDS - Total Dissolved Solids or the Total Conductive Ions
in a solution. See Conductivity Conversion to TDS,
pg. 21.
Tempco - Temperature Compensation
See Temperature Compensation, pg. 19.
For details on specific areas of interest refer to Table of Contents.
NOTES
26 27
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