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Iwaki America Inc.
WEL Series
pH/ORP ELECTRODES
Instruction Manual
Five Boynton Road Hopping Brook Park Holliston, MA 01746
TEL: 508-429-1110 Web: www.walchem.com
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Notice
© 2019 WALCHEM, An Iwaki America Incorporated Company (hereinafter “Walchem”)
5 Boynton Road, Holliston, MA 01746 USA
(508) 429-1110
All Rights Reserved
Printed in USA
Proprietary Material
The information and descriptions contained herein are the property of WALCHEM.
Such information and descriptions may not be copied or reproduced by any means,
or disseminated or distributed without the express prior written permission of
WALCHEM, 5 Boynton Road, Holliston, MA 01746.
This document is for information purposes only and is subject to change without
notice.
Statement of Limited Warranty
WALCHEM warrants equipment of its manufacture, and bearing its identication
to be free from defects in workmanship and material for a period of 24 months for
electronics and 12 months for mechanical parts and electrodes from date of delivery
from the factory or authorized distributor under normal use and service and
otherwise when such equipment is used in accordance with instructions furnished by
WALCHEM and for the purposes disclosed in writing at the time of purchase, if any.
WALCHEM’s liability under this warranty shall be limited to replacement or repair,
F.O.B. Holliston, MA U.S.A. of any defective equipment or part which, having been
returned to WALCHEM, transportation charges prepaid, has been inspected and
determined by WALCHEM to be defective. Replaceable elastomeric parts and glass
components are expendable and are not covered by any warranty.
THIS WARRANTY IS IN LIEU OF ANY OTHER WARRANTY,
EITHER EXPRESS OR IMPLIED, AS TO DESCRIPTION,
QUALITY, MERCHANTABILITY, FITNESS FOR ANY
PARTICULAR PURPOSE OR USE, OR ANY OTHER MATTER.
P/N 180109.Q
April 2019
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Table of Contents
1.0 Operation............................................................ 3
2.0 Installation.......................................................... 5
3.0 Maintenance....................................................... 9
4.0 Specications..................................................... 12
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1.0 Operation
The parts included vary with the model ordered. The electrode assembly always consists
of a replaceable pH or ORP electrode cartridge and a housing. The housing may contain
an optional temperature compensation element, a reliable differential - type preampli-
er with solution ground and/or a 4-20 mA transmitter. For in-line mounted models, a
molded tee or machined adapter are combined with and a mounting nut and o-ring.
Electrode Cartridges:
There are several housings available. Each is best suited for specic applications:
WEL-PHF-NN is a at surface glass pH electrode which will function well in almost any
application, and will perform especially well if the solution tends to coat an electrode
with solids or oils.
WEL-PHB-NN is a bulb-type glass pH electrode which will function well in clean
chemical applications.
WEL-PHH-NN is a at surface glass pH electrode which is highly resistant to attack by
acidic uoride solutions that would quickly etch the glass of a standard pH electrode.
WEL-PHLI-NN is a at surface glass pH electrode with a special gel suitable for use in
low ionic strength water, with conductivity between 10 and 100 µS/cm.
There are two choices of ORP electrode cartridge.
The WEL-MVF-NN is a at surface platinum electrode which will work in almost any
application.
The WEL-MVR-NN uses a platinum rod and is used where the oxidizer level is below
0.25 mg/l.
Electrode Housings:
There are six housings available, which are selected based upon the type of electrode
cartridge used, and the type of instrument to be connected:
The 102581 housing contains a Pt1000 automatic temperature compensation (ATC) element
and differential preamplier with solution ground. This housing is specied in pH
applications when the error due to changing temperature is signicant to your process
(see table below), and the instrument that the electrode will connect to either does not
have an integral preamplier or if the distance between the instrument and the electrode
will exceed 20-30 feet. It should not be specied for ORP applications, since no ATC is
used. It is supplied with a 20 ft. cable with tinned leads and it is dressed for use with the
W400, WebMaster and WIND series controllers.
The 191653-20 housing is identical to the 102581 housing except its cable is dressed
for use with the W100W, W100P, W600 and W900 series controllers
.
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The 102606 housing contains only the differential preamplier with solution ground,
and does NOT contain the Pt1000 ATC element. This housing is specied when the
error due to temperature is insignicant to your process, and the instrument you will attach
does not have a preamplier in it, or is more than 20-30 feet away. It would also be used
with an ORP cartridge, since there is no ATC used in ORP applications. It is supplied
with a 20 ft. cable with tinned leads and it is dressed for use with the W400, WebMaster
and WIND series controllers.
The 191652-20 housing is identical to the 102606 housing except its cable is dressed for
use with the W100W, W100P, W600 and W900 series controllers.
The 102582 housing contains only the Pt1000 ATC element with solution ground, but
does NOT contain the preamplier. This is used in pH applications where the error due
to temperature is signicant to your process, and the instrument to be attached contains
an integral preamplier, and will be located within 20-30 feet of the electrode. It should
not be used in ORP applications. It is supplied with a 20 ft. cable with a BNC connector for
the pH signal and tinned leads for the ATC and solution ground signals and it is dressed for
use with the WPHBW100 series controllers or external preamp box.
The 102607 housing contains neither an ATC element, nor the preamplier. It should
be used in pH or ORP applications where the error due to temperature is insignicant
to your process, and the instrument to be attached contains an integral preamplier, and
will be located within 20-30 feet of the electrode. It is supplied with a 20 ft. coax cable
with a BNC connector and it is suitable for use with the WPHBW100 series controller
or external preamp box.
The 191989 housing contains an internal Pt1000 ATC element, and a transmitter to
convert the pH mV signal to an isolated 4-20 mA signal proportional to 0-14 pH. It is
used to connect to any controller, PLC, SCADA, recorder, or datalogger with a 4-20 mA
input.
The 191988 housing is similar to the 191989, except it is used for ORP cartridges, and
so has no ATC element and the 4-20 mA signal is proportional to -500 to 1000 mV.
pH Temperature Error Table:
°C 2 3 4 5 6 7 8 9 10 11 12
5 .30 .24 .18 .12
15 .15 .12
.09 .06 .03
25 0 0 0 0
35 .15 .12
.09 .06 .03
45 .30 .24 .18 .12
.06
0
.06
.06
0
.03 .06 .09
0
0
0
.03 .06 .09
0
.06
0
.12 .18 .24 .30
.12 .15
0 0 0 0
.12 .15
.12 .18 .24 .30
55 .45 .36 .27 .18 .09 0 .09 .18 .27 .36 .45
65 .60 .48 .36 .24 .12 0 .12 .24 .36 .48 .60
75 .75 .60 .45 .30 .15 0 .15 .30 .45 .60 .75
85 .90 .72 .54 .36 .18 0 .18 .36 .54 .72 .90
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Mounting Adapters:
For in-line applications, included will be either a custom tee or mounting adapter that
ts into a standard tee, and the nut and o-ring that secures the housing to the adapter.
r submersion applications, all that is required is a standard 1” NPTF threaded coupling
Fo
and the appropriate length of 1” pipe. These parts are supplied by the user.
2.0 Installation
General Guidelines
Note: After removing the electrode from the soaker bottle, be sure to remove the large
o-ring from the electrode. This o-ring prevents soaker solution from leaking out of the
bottle and is not part of the electrode.
Instructions for mounting the electrode into the process solution will vary greatly with
the type of electrode and the circumstances that are encountered in your application.
Here are some general guidelines to assist you. Refer also to the typical installation
drawings.
The electrode should be mounted such that the measuring surfaces will always stay wet.
If the electrode dries out, it will respond slowly to changing pH/ORP values for 24
hours, and if dried out repeatedly, will fail prematurely.
For submersion applications, mount the electrode below the minimum solution level. If
the tank will be completely drained, plan on removing the electrode and storing it in tap
water (NOT DI water) or pH 4 buffer solution while the tank is empty. If this is undesirable, a recirculation loop may be installed and the electrode mounted in-line.
For in-line applications, where the electrode is installed in a pipe, the electrode should be
placed on the discharge side of the pump (under positive pressure). A “U” trap should be
installed so that if the flow stops, the electrode is still immersed in the solution. If the
flow through the pipe can not be stopped to allow for cleaning and calibration of the
electrode, then the electrode should be placed in a by-pass line with isolation valves to
allow for electrode removal. Install the electrode vertically, with the measuring surface
pointing down, at least 5 degrees above horizontal. (Refer to Installation drawings)
The electrode should be installed in an area where there is good solution movement and
where it will respond rapidly to chemical additions. The placement of the electrode relative to the placement of chemical replenishment, along with the quality of the mixing,
and the replenishment pump flow rate are all critical to accurate process control.
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Typical Installation
FLOW OUTFLOW IN
SUBMERSION
ELECTRODE
pH
PROBE
ACID
BASE
COOLING TOWER
1
2
3
AC POWER
HEAT
EXCHANGER
METERING
PUMPS
In-line Installation
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ELECTRODE
CARTRIDGE
20 FT CABLE
ELECTRODE HOUSING WITH PREAMP
IN-LINE MOUNT
¾" NPTF TEE (P/N 102884)
20 FT CABLE
MAXIMUM
ELECTRODE HOUSING WITHOUT PREAMP
IN-LINE MOUNT
NUT
(P/N 102586)
¾" NPTF TEE (P/N 102884)
BNC
OPTIONAL
ATC
O-RING
(P/N 102594)
ELECTRODE
CARTRIDGE
NUT
(P/N 102586)
O-RING
(P/N 102594)
Electrode Assembly
For submersion applications, attach the threaded end of the housing to a 1” NPTF
coupling and appropriate length of 1” pipe. This should be sealed to prevent the solution
from contacting the electrode housing cable. Remove the protective cap from the end
of the electrode cartridge, and thread the cartridge into the housing until it is hand tight.
The o-ring should seat against the housing.
20 FT CABLE
1" PIPE
1" NPTF COUPLING
(USER SUPPLIED)
ELECTRODE
CARTRIDGE
ELECTRODE HOUSING WITH PREAMP
SUBMERSION MOUNT
20 FT CABLE
MAXIMUM
1" PIPE
1" NPTF COUPLING
(USER SUPPLIED)
ELECTRODE
CARTRIDGE
ELECTRODE HOUSING WITHOUT PREAMP
SUBMERSION MOUNT
OPTIONAL
ATC
BNC
For in-line applications, feed the electrode housing cable through the adapter nut. Remove
the protective cap from the end of the electrode cartridge, and thread the cartridge into the
housing until it is hand tight. The o-ring should seat against the housing. Place the large
o-ring into the mounting adapter groove, then place the electrode housing into the tee,
and thread the adapter nut onto the tee until it is hand tight.
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Wiring Instructions
For housings that contain the integral preamplier, attach the 7-conductor cable directly
to the controller:
If the required cable length exceeds the 20 feet that is supplied, wire the housing to a
190851 terminal box, then use p/n 102535 cable to reach the instrument.
For housings that contain the integral 4-20 mA transmitter, the wires have the following
purposes:
RED: +
BLK: SHIELD: SHIELD
For Walchem analog inputs, use the wiring instructions for the specic input board for an
input type of 2-wire unpowered transmitter.
For housings that do not contain the integral preamplier, attach the male BNC connector
on the housing to the female BNC connector on the instrument, and the optional temperature
wires to the temperature input terminal strip on the instrument:
RED TC (polarity not critical for TC)
BLK: TC (polarity not critical for TC)
[TC= Temperature Compensation]
The non-amplied signal is extremely sensitive! Never cut, splice or otherwise harm the
integrity of the coaxial cable or BNC connector! If the distance between electrode and
instrument exceeds 20 feet, use the housing that contains a preamplier, or purchase an
externally mounted preamplier.
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3.0 Maintenance
The Combination pH/Reference Electrode or ORP (REDOX) Reference Electrode is ruggedly
made and easy to use. Because the pH responsive glass bulb or at surface is relatively thin,
care should be taken so that the bulb does not become scratched or broken. It is also important
that ORP measuring surfaces are not scratched or gouged. The suggestions in this sheet are
intended to help avoid these problems.
The built-in sealed reference design of this electrode eliminates the need to add lling solutions
and minimizes reference dryout. This design feature also allows the electrode to be used in
pressurized systems (refer to specication sheets or consult the factory for maximum pressure/
temperature limit information).
Important Considerations
1. The pH Electrode is shipped in a plastic bottle or cap containing a solution of 4 buffer
and potassium chloride. ORP (REDOX) Electrodes are shipped in caps containing a
piece of cotton wetted with tap water. The electrode should remain in the bottle
or cap until it is used. If the electrode is used infrequently, the bottle or cap and its
solution should be saved and the electrode stored in it.
2. Electrodes are a form of a battery and have limited shelf lives. Electrodes in inventory
should be rotated so that older electrodes are used rst.
3. Vigorous stirring brings a sample, buffer or rinse solution to the measuring surface
more quickly and will improve speed of response. Care must be taken to keep the electrode’s
measuring surface from striking a surface and getting scratched or broken.
4. After exposure to a sample, buffer or rinse solution, carryover can be minimized by
blotting - never by wiping - the electrode with a clean, non-abrasive paper or a clean
cloth towel.
5. As a rinse solution, use a part of the next sample or buffer which is to be measured.
This action also will minimize contamination from carryover.
6. When calibrating, use a buffer close in value to that expected from the sample for 1
point calibrations or as the rst buffer for 2 point calibrations (see below). This action
will minimize span errors.
7. Readings stabilize faster in some solutions than others; allow time for the reading to
stabilize. In general, with new electrodes stable readings in buffers are obtained in 1015 seconds.
8. All pH electrodes age with time. Aging is characterized by shortened span and slower
speed of response. Aging is best detected by the 2 point calibration method. If the pH
meter has manual or microprocessor slope (span) controls, the controls can be adjusted
to compensate for electrode span errors (but will not affect the speed of the response).
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9. Electrodes should be replaced when their readings cannot be corrected by the
meter’s controls and/or when their speed of response is too slow for the application
for which they are being used. The frequency of electrode replacement is a function
of the application; electrodes operating in hot liquids at very high or very low pH
values will have shorter lives than those operating at neutral pH and ambient temperature.
10. Coatings on an electrode’s surface prevent new liquids from contacting an electrode’ s
measuring surface and can mimic the effects of electrode aging. Before concluding
that an electrode needs replacing, check the surface for coatings.
11. Temperature affects electrode readings in two ways. First, the output of an electrode
varies with temperature. For pH electrodes this effect can be corrected by manual
or automatic temperature compensation (ORP/REDOX readings are not correctable
for the effect of temperature changes). Second, the real pH or ORP value, independent
of the electrode measuring the value or the use of temperature compensation, is temperature
dependent. This fact means, for example, that the readings at 25°C and 75°C will be (and,
in fact are) different.
CALIBRATION
As a rule, follow the procedure shown in the pH Meter’s Instruction Manual. These procedures will vary depending on whether the meter is a simple type with manual adjustments, a micro-processor type or a pH transmitter.
FREQUENCY OF CALIBRATION
The frequency of calibration is a function of many factors. These factors include:
1. The accuracy required by the application.
2. The value of the off-specication product versus the cost of calibration.
3. The coating or abrasive nature of the application.
4. The stability of the pH Electrode and pH Meter as a system.
The frequency of calibration is really determined by experience. At a new installation, calibration might initially be checked every few hours or shift with the calibration
changes noted in a log. As a pattern of longer stability is found, the time between calibration checks can be increased to once a day or once a week. Although the frequency of
calibration is solely the responsibility of the user, once a week is the longest recommended interval between calibrations.
SYSTEM CALIBRATION CONCEPTS
The pH Electrode and the pH Meter should always be calibrated as a system. Electronic
calibration of a pH Meter with a pH signal simulator checks the meter only and does not
correct for imperfections of the pH Electrode. Even if perfect when new, the performance of pH electrodes varies with time, usually in an unpredictable way. When changing electrodes or connecting an electrode to a different pH meter, re-calibration must be
performed.
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Page 12
SINGLE POINT CALIBRATIONS
Single point calibrations involve the use of one pH buffer. They are the easiest to make
but can provide misleading results. They should only be used for quick checking from
time to time.
TWO POINT CALIBRATIONS
As their name implies, 2 point calibrations use 2 pH buffers: for example, buffers 7.00
and 4.00 or buffers 7.00 and 10.00. Two point calibrations correct for the pH electrode’s
offset and span errors. Since both the offset and span vary with time, the 2 point method
is the preferred one.
GRAB SAMPLE CALIBRATIONS
The Grab Sample Calibration method is used when it is difcult or undesirable to
remove an electrode from a system. This method involves obtaining a sample of the
liquid being measured and noting the meter’s reading at that time. The sample’s reading
is obtained by use of a calibrated lab or portable meter and that reading is compared to
that of the on-line meter. The on-line meter is adjusted by the difference between the
readings. It is important to use the difference between the readings because the system’s
reading may have changed in the intervening time. It is important that the sample being
measured by the lab meter be at the process temperature or erroneous results may occur
(See #11 on the previous page).
CALIBRATION PROCEDURES
Stepwise calibration procedures are noted in the pH Meter’s Instruction Manual. The
following suggestions will help make calibrations as accurate as possible:
1. Before placing the electrode in a new buffer, use an absorbent paper towel or clean
absorbent cloth to blot, not wipe, off any liquid that clings to the electrode. This action
will minimize carry-over that could contaminate the buffer.
2. Always use fresh buffers. Safely dispose of the buffers after they have been used for
calibration. Do not return them to their bottles; this action could contaminate the
buffers.
3. Stir the electrode in the buffer to make certain that the fresh buffer quickly reaches
the electrode’s measuring surface.
INTERMITTENT OPERATION
Some facilities are only operated part of the time. When out of operation, electrodes
must not be allowed to be exposed to air and become dry. Electrodes should be removed
from such systems and stored in their bottles and caps or in a beaker, lled, preferably
with 4 buffer. In some instances, power to the meter is shut off; this condition can be
harmful to the electrodes. Electrodes should be disconnected from un-powered meters.
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ELECTRODE CLEANING
Coating of an electrode’s measuring surface can lead to erroneous readings including
shortened span and slow response times. The type of coating determines the type of
cleaning technique.
Soft coatings can be removed by vigorous stirring, by use of a squirt bottle, or very
carefully, by gently wiping with a soft, clean non-abrasive paper or cloth. Hard coatings
should be chemically removed. The chemical used to remove the coating should be the
least harsh chemical that dissolves the coating in 1 or 2 minutes and does not attack the
electrode’s materials of construction. For example, a calcium carbonate coating might
be removed with 5% HCl (muriatic acid).
Oily or organic coatings are best removed with detergents or an appropriate solvent
that does not attack the electrode’s materials of construction. For example, isopropyl
alcohol might be used but acetone should be avoided if the electrode’s body is made of
CPVC.
Note: When using chemicals or solvents, care should be taken and appropriate eye,
face, hand, body and/or respiratory protection should be used.
Never abrade or sand a pH electrode’s surface. However, the measuring surface of an
ORP/REDOX electrode may be gently abraded by use of 600 grade wet silicon carbide
paper, jewelers rouge or very ne steel wool.
4.0 SPECIFICATIONS
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Page 14
Bar
24.1
20.7
17.2
13.8
10.3
6.9
3.4
PSI
350
300
250
200
150
100
50
Pressure (PSI) vs. Temperature (F)
0
30
40
50
60
70
80
90
100
110
120
130
140
150
160
°F
170
180
-1.1
4.4
10.0
15.5
21.1
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26.6
32.2
37.7
43.3
48.8
54.4
60.0
65.5
71.1
76.6
82.2
°C
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Five Boynton Road Hopping Brook Park Holliston, MA 01746
TEL: 508-429-1110 FAX: 508-429-7433 Web: www.walchem.com
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