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OPERATING INSTRUCTION MANUAL
Model ES-5
Toroidal 4-20 mA Output Probe
N116-127 REV. 3
Aquametrix, by Water Analytics Inc.
100 School Street
Andover, MA 01810
Tel: (978) 749-9949
Toll Free: (855) PH-PROBE
Fax: (978) 749-9961
www.AquaMetrix.com
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ES-5 Toroidal Sensor Manual
Table of C ontents
1!General Information
...................................................................................................................... 3!
2!Specifications
................................................................................................................................ 3!
3! Introduction to Conductivity ............................................................................................................ 3!
3.1!What is Conductivity?
..................................................................................................................................................... 3!
3.2!Principle of Toroidal Cell Operation
......................................................................................................................... 6!
3.3!Advantages of the Electrodeless Conductivity System
................................................................................... 6!
3.4!Temperature effects
......................................................................................................................................................... 6!
4! Installation ...................................................................................................................................... 6!
4.1! Electrode Connections ..................................................................................................................................................... 6!
4.2! Positioning of the Sensor ................................................................................................................................................. 7!
5! Operation ....................................................................................................................................... 7!
5.1!Calibration
............................................................................................................................................................................ 7!
5.2!Sample Requirements
.................................................................................................................................................... 7!
5.3!Measurement
...................................................................................................................................................................... 8!
5.4!Cleaning Methods
............................................................................................................................................................ 8!
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1 General Information
The ES-5 Conductivity Monitoring System consists of:
1. A loop powered micro-transmitter and an electrodeless conductivity sensor combined into a single
package. The probe consists of two measuring toroidal coils and a 4/20 current loop calibrated
transmitter.
2. RTD PT100 built into the sensor to provide Temperature Compensation.
Applications include water treatment, cooling tower and water monitoring.
2 Specifications
Measuring Method
Toroidal
Range ES-5-C-1
0-10 mS/cm
Range ES-5-C-2
0/100 mS/cm
Range ES-5-C-3
0/1000 mS/cm
Power Supply
11/30 VDC
Current Loop
4/20 mA isolated
Load
600 Ω max. @ 24 VDC
Installation
In-line or Immersion
Cell
Inductive
Temperatur e Co mpen sation
RTD PT100
Maximum Operating Temperature
50 oC for part in contact with the liquid
Temperature Coeff icient
2.2%/°C
Temperatur e Refer ence
25 °C
Maximum Pressure
10 bar at 25 °C
Length
207 mm
Thread
1.5" MNPT
Materials
CPVC (Kynar upon special request)
Cable Length
3 meters (other upon request)
3 Introduction to Conductivity
3.1 What is Conductivity?
Conductivity (or specifically electrolytic conductivity) is defined as the ability of a substance to conduct
electric current. It is the reciprocal of the more commonly encountered term, resistivity. All substances
possess conductivity to some degree, but the amount varies widely, ranging from extremely low
(insulators such as benzene, glass) to very high (silver, copper, and metals in general). Most industrial
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interest is in the conductivity measurement of liquids. Electric current will readily flow through some
liquids. The less ordered arrangement of the liquid molecules is not conducive to free electron movement.
Therefore , another sort of c harged particle mu st se rve th is pur pose i f any current is to flow at all. In solvents
where electrical conductance occurs, notably in water, ionization will provide the needed carriers.
Ionization refers to the tendency of most soluble inorganic compounds to partially or completely
separate into two or more elemental components, called ions, having opposite electrical charges. These
charged particles, or ions, act as current carriers producing electrolytic current flow. It is the physical
characteristics of the carriers as much as that of the medium that determines electrical conductance of a
solution. These solutions have conductivities approximately midway between insulators and metallic
conductors. This conductivity can be measured quite easily by electronic means, and this offers a simple
test, which can tell much about the quality of the water, or the makeup of the solution. A broad line of
conductivity equipment is available to measure liquids ranging from ultrapure water (low
conductivity) to concentrated chemical streams (high).
Advantages and Constraints of Conductivity Measurement
In general, conductivity offers a fast, reliable, nondestructive, inexpensive and durable means of
measuring the ionic content of a sample. Reliability and repeatability are excellent.
The pr inci ple dr awb ack of co nduc tiv ity is th at it is a n ons peci fic me asur eme nt; it can not dis tin gui sh between
different types of ions, giving instead a reading proportional to the combined effect of all ions present.
The refor e it mus t be applied with some prior knowledge of the solution composition or used in relatively
pure (single solute) solutions to be successful.
Units of Conductivity
The units of measurement used to describe conductivity and resistivity are quite fundamental and are
frequently misused. Once the units are known, various waters can be quantitatively described.
The basic unit of resistance is th e fam iliar ohm. Conductance is the reciprocal of resistance, and its
basic unit is the Siemen, formerly called mho. In discussions of bulk material, it is convenient to talk of its
specific conductance, now commonly called its conductivity. This is the conductance as measured between
the opposite faces of a 1-cm cube of the material. This measurement has units of siemens/cm. The units
microSiemens/cm (µS/cm) and milliSiemens/cm (mS/cm) are most commonly used to describe the
conductivity of aqueous solutions. The corresponding terms for specific resistance (or resistivity) are
ohm-cm (Ω-cm), megaohm-cm (MΩ-cm) and kilohm-cm (kΩ-cm).
Users of ultrapure water prefer to use resistivity units of MΩ-cm, because measurement in these units span
the typical range of interest. These same users frequently use kΩ-cm when dealing with less pure water
such as tap water. Others, however, use the units of S/cm and mS/cm when dealing with any stream from
quite pure to very concentrated chemical solutions. In these applications, the use of conductivity has the
advantage of an almost direct relationship with impurities, especially at low concentration. Hence, a rising
conductivity reading shows increasing impurities, or a generally increasing concentration in the case of a
chemical stream (with some exceptions in concentrated solutions). See
Table 1
for a comparison of
resistance and conductivity
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Tabl e 1 - Conductivity - Resistivity - TDS Conversion
Conductivity (µS/cm)
Resistivity (Ω-cm)
Dissolved Solids (ppm)
0.056
18000000
0.028
0.084
12000000
0.042
0.167
6000000
0.083
1.00
100000
0.500
2.50
400000
1.25
20.0
50000
10.0
200
5000
100
2000
500
1000
20000
50
10000
Table 2
lists conductivity value of common aqueous solutions. Conductivity is
approximately proportional to concentration of ions from salts but is highly non-linear
as a function of concentration for acids and bases.
Tabl e 2 - Conductivity of Various Aqueous Solutions at 25 oC
Solution
Conductivity
Resistivity
Pure Water
0.055 µS/cm
18.3 MΩ-cm
Power Plant Boiler Water
1.0 µS/cm
1 MΩ-cm
Distilled Water
0.5 µS/cm
2 MΩ-cm
Deionized Water
0.1-10 µS/cm
0.1-10 MΩ-cm
Demineralized Water
1-80 µS/cm
0.01-1 MΩ-cm
Mountain Water
10 µS/cm
0.1 MΩ-cm
Drinking Water
0.5-1 mS/cm
1-2 KΩ-cm
Wastewater
0.9-9 mS/cm
0.1-1 KΩ-cm
KCl Solution (0.01M)
1.4 mS/cm
0.7 KΩ-cm
Potable Water Maximum
1.5 mS/cm
0.7 KΩ-cm
Brackish Water
1-80 mS/cm
0.01-1 KΩ-cm
Industrial Process Water
7-140 mS/cm
Rarely Stated
Ocean Water
53 mS/cm
Rarely Stated
10% NaOH
355 mS/cm
Rarely Stated
10% H2SO
4
432 mS/cm
Rarely Stated
31% HNO3
865 mS/cm
Rarely Stated
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3.2 Principle of Toroidal Cell Operation
The ES-5 electrodeless conductivity sensor employs two toroidally wound coils
in close proximity to each other. An alternating current is applied to one of the
coils, generating an electric field in the solution being measured. The second
toroidal coil acts as a receiver to detect the small current formed from ion
movement in the conducting loop of solution, which is proportional to the solution
Conductivity. The entire assembly is encapsulated in CPVC, so no metallic
contact with the solution occurs.
3.3 Advantages of the Electrodeless Conductivity System
The design of th e electrodeless conductivity system eliminates any form of
polarization, so accurate readings in all types of solutions are possible.
Electrode contamination, which can lead to erroneous readings, is also not a
problem. Since the conduction process occurs in a volume of solution, any fouling
(such as a coating of oil formed on the probe) merely reduces the conductivity reading
by the insignificant amount of volume reduction.
The CPVC e nca psulat ion pr events any s olutio n to m etallic c ontact , the reby
eliminating the possibility of gas formations at the electrode surface, which can occur
using the more conventional contacting type conductivity systems.
The electrodeless conductivity probe measures up to the highest known
conductivity (approximately 1 S/cm) with great accuracy.
3.4 Temperature effects
Conductivity has a substantial dependence on temperature. This dependence is
usually expressed as percent/oC at 25oC. Ultrapure water has the largest
dependence on temperature, at 5.2%/oC. Ionic salts has a dependence of about
2%/oC, with acids, alkalis, and concentrated salts solutions are around 1.5%/oC.
Temperature variation causes frequent problems with conductivity measurements
when the solution under testing has a rapid varying temperature. The change in
conductivity is instantaneous, since it is an electrical measurement. The thermistor,
however, has a response time of 15 seconds to several minutes. A good rule of
thumb is to allow 5 times the time it takes for the thermistor to respond to allow
the reading to stabilize. Any sudden dips or peaks should be ignored during this
time.
4 Installation
4.1 Electrode Connections
The ES-5 is a two-wire, loop-powered sensor so there are only two connections plus
an optional ground. Figure 1 shows the electrical connections.
1. Connect the white wire of the electrode to the signal input.
2. Connect the black wire of the electrode to 24 VDC.
3.
Connect the bare silver ground wire of the electrode to ground. It can
be left unconnected in most applications.
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Figure 1 - Electrical Connections of the ES-5. The clear wire connects to the 24
VDC of the current loop and the black wire connects to the signal input.
4.2 Positioning of the Sensor
The ES-5 comes with two 1.5” MNPT threads—on the front and back end. In tank
applications the ES-5 mounts on to the end of a submersion arm that terminates
via the rear 1.5” FNPT thread. AquaMetrix sells the STC60L submersion arm for this
purpose. For mounting in a pipe a union tee is required. Because of the insertion
depth only pipes with a pipe diameter greater than 4” may be used.
It’s very important that the sensor does not contact the walls of the container or
pipe as that will cause a decrease in the observed conductivity reading.
5 Operation
5.1 Calibration
1. Place electrode in the air. Calibrate the meter to read 0.00 by turning
the setscrew on the zero control of the controller.
2. Prepare a 10, 95.5, or 500 mS/cm conductivity standard depending on
the measurement range of the toroidal cell connected to the controller. To
make a 10 mS standard, dissolve 11.4 g KCl (potassium chloride) in 2 liter of
distilled water. To make a 95.5 mS standard, dissolve 200 g KNO3 (potassium
nitrate) in 2 liter of distilled water. To make a 500 mS/cm standard, dissolve 200
ml of concentrated HNO3 (nitric acid) in 2 liters of distilled water.
3. Place the electrode into the selected conductivity standard placed in a 2-liter
beaker. Do not stir. Do not allow the electrode to be in contact with the
walls or the bottom of the beaker. The electrode should react
immediately and show a rapid increase in the reading. After 60 seconds,
calibrate the meter to read the value of the standard.
5.2 Sample Requirements
For maximum accuracy and efficiency, the conductivity probe must meet
the following requirements: - The sample in the cell mu st be rep resentative
of the whole solution.
1. The solution must circulate continuously through the cell.
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2. The flow velocity must not be so high as to cause cavitations.
3. The position /orientation of the cell m ust not t rap air bu bbles near the
electrode area.
4. Sediment must not accumulate within the electrode area.
5. For immersion applications, the water must be continuously agitated.
6. For in-line applications, 100mm is the minimum size pipe the cell may be
installed in. The probe has a 1.5-inch MNPT fitting for screwing into a pipe.
7.
Keep the overall length of cabling away from power wires.
5.3 Measurement
After immersion or mounting the electrode, read the conductivity value in mS
directly from the controller display.
5.4 Cleaning Methods
For most applications, hot water mixed with domestic cleaning detergent
can be used for cleaning.
1. For lime and other scaling
compounds
, clean with a 5-10% solution of
hydrochloric acid.
2. For solutions containing organic fouling agents (fats, oils, etc.), clean
probe with acetone or alcohol.
3.
For algae and bacteria containing solutions, clean the probe with a
bleach solution and a soft brush.
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