Conductivity Analyzers

Yokogawa is a recognized world leader for reliable conductivity equipment, providing credible and repeatable measurement solutions for maintaining and controlling even the most demanding process applications.

Yokogawa offers conductivity analyzers suitable for measuring the two most common conductivity measurement methods: contacting and inductive (also known as toroidal or electrodeless). Our conductivity analyzers provide high precision measurement and are built to withstand the harshest applications, requiring minimum maintenance and helping you achieve increased efficiency and reduced operating costs.



  SC450G/ISC450G FLXA202/21 FLXA402 DC402

Area Classification General Purpose, Class I Div II General Purpose, Class I Div II, Class I Div I General Purpose, FM Class I Div II pending Class I Div II
Power Supply 4-Wire 110-256 VAC, Mains Power; 4-Wire 24 VDC 2-Wire Loop Powered 24VDC 4-Wire 100-240 VAC; 4-Wire 12-24 VDC 4-Wire 110-256 VAC, Mains Power
Communication 4-20mA, HART 4-20mA, HART, FF and PA* 4-20mA, HART, Ethernet (Modbus TCP), RS-485 (Modbus RTU) 4-20mA, HART
Contacts and Relays 4 SPDT relay contacts with display indicators N/A 4 SPDT relay contacts with display indicators 4 SPDT relay contacts with LED indicators
Measurement Type Contacting Conductivity, Resistivity, Percent Concentration (SC450G)
Inductive, Toroidal, Non-Contacting Conductivity, Percent Concentration (ISC450G)
Contacting Conductivity, Resistivity
Inductive Conductivity, Percent Concentration
pH, ORP (oxidation- reduction potential) , Contacting Conductivity, Resistivity
Inductive Conductivity, Percent Concentration, Dissolved Oxygen and 4-20 mA input
Universal Conductivity/Resistivity

*FF and PF available in the Plastic FLXA21 for contacting conductivity and resistivity

  • The FLEXA™ series analyzers are modular-designed analyzers used for continuous online measurements in industrial installations. They offer single or multi-sensor measurement.


  • The EXAxt450 series covers all Conductivity Applications including all special software functions in the standard analyzers to reduce the number of configurations. This results in less inventory and less training needs for users that have multiple Conductivity applications.

  • The FLEXA™ series analyzers are used for continuous on-line measurements in industrial installations. With an option for single or dual sensor measurement, they are the most flexible two-wire analyzer available.

  • Designed to accept two sensor inputs. Differential, ratio, deviation, % passage or % rejection can be indicated and/or transmitted.

  • Compact, lightweight, and dripproof, the SC72 is the ideal Conductivity meter for field use. Features wide-range auto-ranging, automatic temperature compensation, self-diagnostic functions, and a large, easy-to-read LCD display.

Water Purification

Brine Manufacturing
Brine is often used within industrial processes such as food and beverage, refineries, textile dyeing house, and chemical plants as well as in municipalities or for commercial use as a final product applied to pavement roadways or commercial parking lots as an anti-icing or de-icing agent.

Conductivity measurement can be used as a reliable indicator of the real-time brine concentration. Utilizing online process analyzers removes the need for timely grab sample analysis. Yokogawa’s inductive conductivity analyzers help you achieve increased efficiency and reduced operating costs while realizing reliable brine concentration measurements.

Boiler Blowdown
The frequency and duration required for boiler blowdown is significantly affected by water quality. Raw water used to feed the boilers contains varying levels of impurities that must be removed to protect the boiler and associated equipment. Pretreatment processes such as reverse osmosis, ion exchange, filtration, softening and demineralization may be used to reduce the level of impurities. Unfortunately, even the best pretreatment processes will not remove all impurities and will continuously carry some dissolved mineral impurities into the boiler.

Improving feedwater quality through make-up water, chemical treatment, and proper blowdown control can significantly reduce costs including:

  • Reduced operating costs
  • Reduced maintenance and repair costs
  • Cleaner and more efficient steam
  • Energy savings
  • Increase efficiency and reduce operating costs using Yokogawa’s conductivity products.


Pharmaceutical Waters
Yokogawa’s conductivity transmitters and converters possess USP (United States Pharmacopoeia) functions to simplify and automate USP requirements. The FLEXA two-wire conductivity transmitter has the USP23/24 Stage One table pre-programmed in its software. When enabled, the transmitter will send a FAIL signal when the water exceeds the USP limit and can display and transmit the uncompensated conductivity that USP mandates for compliance recording.

The SC450 and DC402 four-wire conductivity converters have additional USP features with the ability to display and transmit the uncompensated conductivity for USP compliance, as well as the NaCl temperature compensated measurement, valuable for process control.

The USP23/24 Stage One table is pre-programmed into these instruments, and a FAIL alarm will be given if the conductivity limits are exceeded. Alarms on these units can be dedicated as USP “warning” alarms with user-defined safety margins. These “warning” alarms will inform the operator that his/ or her water is trending towards the USP limit and will allow him/or her to take preemptive corrective action.


Ion Exchange is a method for the exchange of ions between two electrolytes or between an electrolyte solution and a complex molecule. In most cases, the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic ion exchangers.

The dual channel process liquid analyzer gives you the ability to measure the bed’s inlets and outlets and calculate the ratio or % passage of the bed.


Heat Exchanger Leakage
Corrosion on the process side causes the heat exchanger tubing to mechanically fail, allowing the process fluid to leak into the condensate return line. This can cause serious damage to the boiler. Therefore, it is necessary to monitor the condensate downstream of the heat exchanger and to dump it as soon as it shows signs of contamination.

An excellent indication of contamination can be obtained by measuring the conductivity of the condensate because pure condensate has a very low conductivity value (1 to 10 µS) while contaminates (typically salts, acids or alkalis) that are introduced when leakage occurs have a significantly higher conductivity value. Because of the sizeable differences in values, even the slightest leak will sharply increase the conductivity reading. Any marked increase in the conductivity of the condensate indicates that leakage is present and that the condensate should be sent to drain.

Measurement and control of heat exchanger leakage can help prevent costly maintenance, repair, and downtime. The simple, essentially maintenance-free measurement of condensate conductivity gives operators the necessary information (or provides automatic control) to prevent severe damage to the boiler should a breakthrough of the heat exchanger occur.


Measuring the Electric Conductivity with Clean-in-Place (CIP) System

In the Pharmaceutical, Chemical and Food & Beverage industries, after manufacturing products, the cleaning and sterilization of tanks and piping are done with various cleaning solutions, fresh or hot water and steam. Clean-in-Place (CIP) is a system designed for automatic cleaning and disinfecting.

Yokogawa’s inductive conductivity liquid process analyzer takes measurements with good boundary surface precision over a wide range, earning it a reputation in the recovery of cleaning, which contributes significantly to reduce chemical and wastewater processing costs.

Percent Concentration

There are numerous industrial applications where measurements and/or control of a specific chemical strength of the process is critical for optimizing the production of the end product. These specific concentrations are obtained by mixing a full strength solution with water to achieve the desired percent concentration. Conductivity measurement is a reliable indicator of the concentration of most acid or base solutions.


In a semiconductor plant, a variety of chemicals are used in various manufacturing processes. The chemicals used for specific purposes are produced by diluting raw liquid with demineralized water using in diluting equipment, and the control of the concentration at this point is performed by conductivity measurement. 

Application Note

To defray energy costs, many industrial plants have their own boilers to generate steam to produce a portion of their energy needs. In addition to generating power, the steam may also be used directly in plant processes or indirectly via heat exchangers or steam jacketed vessels. 


Reverse osmosis (RO) is a separation process that uses pressure to force a solution through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.

Application Note

The kraft process (also known as kraft pulping or sulfate process) describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers. Wood chips are by harsh chemicals (white liquor) to produce pulp and spent liquor (black liquor).

Application Note


The United States Pharmacopoeia (USP) and European Pharmacopoeia (EP) regulations require total organic carbon (TOC) to be monitored in pharmaceutical waters. Implementing these guidelines is required for companies that bring drugs to the US market. These guidelines are contained in the USP monograph (article). 

Among other functions, the USP states qualifications for sterility and packaging methods that delineate between the various specific types of water. However, there are two basic types of water preparation, Water for Injection and Purified Water. The analytical standards for these two types of water are very similar, differing in the fact that Water for Injection has stricter bacterial count standards and must also pass the bacterial endotoxin test. Preparation methods are very similar to a point, however, Water for Injection preparation must incorporate distillation or double pass reverse osmosis. Discussion of the various methodologies used in preparation of USP water applies equally to Purified Water (PW) and Water for Injection (WFI). 

There are two main types of water, purified water (PW) and water for injection (WFI). Purified Water is water obtained by distillation, ion-exchange treatment, reverse osmosis, or other suitable process. It is prepared from water complying with the regulations of the U.S. Environmental Protection Agency (EPA) with respect to drinking water. It contains no added substances. And, Water for Injection (WFI) is water purified by distillation or reverse osmosis. 

These waters are used as ingredients in either dose form or bulk pharmaceuticals, so purity is critical. WFI is the purest grade of bulk water monographed by the USP, and is found in the manufacture of parenteral (injected), ophthalmic (eye drops), and inhalation products. The Fundamental objectives of the USP are:

I. To maintain or improve the existing water quality
II. Improvement of the reliability of the measured values by means of modern analytic instruments
III. Reduction of the number of samples
IV. Authorization of the in-line measuring method

USP 23 and 24

Before 1996, the quality of these waters was determined by a number of off-line, “antiquated” laboratory tests. The USP monograph 23 (and currently 24) replaced these tests with an on-line conductivity measurement as the initial marker. While PW only needs to meet a TOC limit, the WFI has to meet bacterial tests in addition to the TOC and conductivity limits. In this application note we will concentrate on the USP requirements for conductivity only. This change to an on-line conductivity measurement was precipitated by many desires including improving the reliability of the testing by using modern instrumentation, providing immediate alarms and options for quality control, eliminating sample collection and handling errors, and reducing the cost of testing. 

The conductivity requirements mandated by USP are tiered in three stages:

Stage One: Use In-line or grab sample methods to measure the conductivity and water temperature. This conductivity reading must not be temperature compensated. Compare these readings to the Stage I graph shown, or the values in table I. If the conductivity is below the limit stated for that temperature, the water meets the requirements. If the conductivity is above the limit, proceed to Stage Two. Advantages to In-Line measurement are:

I. Real-time information for conductivity and temperature
II. Immediate limit value alarm
III. Data output for recording and documentation of the water quality
IV. Simple and reasonably-priced measurement
V. Avoiding errors due to sampling, handling and transport

Stage Two: Take a grab sample and measure the conductivity after equalization with atmosphere and temperature normalization to 25ºC. If the water conductivity is below 2.1 μS then Stage Three is needed. 

Stage Three: If Stage Two is exceeded, measure the pH of the grab sample and check conductivity against the results in table I of conductivity vs. pH. If the sample is within the limits, it passes. If it does not, the water is deemed unacceptable for PW or WFI use. 


Yokogawa’s conductivity transmitters and converters possess USP functions that make this seemingly complex and troublesome requirement pain free, and automatic. The FLEXA two-wire conductivity transmitter has the USP23/24 Stage One table pre-programmed in its software. When enabled, the transmitter will send a FAIL signal when the water exceeds the USP limit. It also can display and transmit the uncompensated conductivity that USP mandates for compliance recording.

The SC450 and DC402 four-wire conductivity converters have additional USP features. These units have the ability to display and transmit the uncompensated conductivity for USP compliance, as well as the NaCltemperature compensated measurement, valuable for process control. The USP23/24 Stage One table is pre-programmed into these instruments, and a FAIL alarm will be given if the conductivity limits are exceeded. Alarms on these units can be dedicated as USP “warning” alarms with user defined safety margins. These “warning” alarms will inform the operator that his/ or her water is trending towards the USP limit, and will allow him/or her to take preemptive corrective action.


The input module you need depends on the Model Number of your FLXA Analyzer.


Use the link at the top of the page to download a compressed (ZIP) file containing the GS Sheet and Manual for the SC150.

  • With an Ohm meter check the following wires on the ISC40G sensor cable:
    • 11 to 12 (Pt1000 or Thermistor)
    • 13 to 17 – Sensor coil – expect low resistance. If unstable or above 100Ω it is bad.
    • 15 to 16 - Sensor coil – expect low resistance. If unstable or above 100Ω it is bad.
    • 14 to every other wire – The ohm meter should stay off scale. If the ohm meter moves/jumps/reads anything that is bad.


Simulating a conductivity reading on an ISC convertor.

  • You will need:
    • A known working ISC Converter
    • A piece of wire
    • One or two decade box/resistance sources.
  • Connect sensor wires 13-17 to analyzer.
  • Connect wire through the toroidal sensor and connect the wire to the decade box. Be sure not to cross the leads or wire.
  • Use second decade box resistance source to simulate the temp sensor.
    • If you don’t have a second resistance source you can just connected the temp sensor wires 11&12 from the sensor, you will just not be able to vary the input readings.
  • Write down the Cell Constant, change it to 1.000
  • Set the temperature to the reference temperature or: Write down the Temp. Compensation method, and change it to “None.”
  • The Conductivity reading should be 1/R where R = Resistance on the decade box.
  • If you need higher resistance than the decade box you can use multiple loops of wire through the sensor.  The reading will be L2 / R where L = Number of loops, R = Resistance on the decade box.
  • Return all settings to the original settings when finished.

There is no way to "turn off" an unused input on a DC402. If you leave the terminals open you will get error messages. 

Connect a simulated sensor to the unused input to clear the errors. Use a resistor on 11-12 to simulate the temp sensor, 1000 ohms for PT1000, 100 Ohms for PT100. Simulate the same type temperature sensor that the other channel is using. 

Use a resistance to simulate the cell that gives a conductivity reading within the range, usually 1000 ohms between 14-15 will work. Once you have connected the resistors the input the errors will clear.


If you forgot the password to your FLXA Transmitter you can use the password #PW123# - this will allow you go into the menus. Remember to change or remove the password.


If you have lost the password for your SC150 you can use password   #PW123#   to get into the menu. The next thing you should do is to reset the password.


If you forget the password you have set in one of these transmitters there are only 9 passwords that can be set. 

The password setting on the unit is a little difficult to understand. When you put a 3 digit code in service code 52 you are setting up 3 passwords, not just 1. The first digit is for the maintenance mode (calibration) The second digit is for the commissioning mode (when you hit the * key) The third digit is for the service menu (when you hit yes on the SERV menu under commissioning). 

Here are the password options: 

1 = 111
2 = 333
3 = 777
4 = 888
5 = 123
6 = 957
7 = 331
8 = 546
9 = 847 

So, and example:

if you setup a password of 1.2.3:

  • To calibrate you would have to enter 111 
  • When you hit the * key the password would be 333
  • To access the SERV menu the password would be 777

There are no bypass passwords, these are the only passwords available for the unit.


To test the conductivity input do the following: 

  1. Write down the cell constant and change it to 1.00 (this is not mandatory, it makes the math easier) 
  2. Place a jumper wire between 13 to 14 and another one on 15 to 16 (not necessary on the DC400/402) 
  3. Place a resistance between the 13/14 and 15/16 connection. If the unit is set in resistivity it should match the resistance. If it is displaying conductivity it should read Y where Y = (cell constant)/(input resistance) and the units are Siemens. So if the result is 0.005 Siemens this equals 5 milliSiemens.and 0.000005 Siemens equals 5 microSiemens. 

Remember to set the cell constant back to the original value if you changed it.




    In this 40 min session you will learn the fundamental requirements for aqueous conductivity measurements; the differences between "Contacting" and "Inductive" measurement techniques and which one to use for a particular application. As well as learn the importance of online diagnostics. The goal is to provide participants with simple techniques they can implement to improve their day to day operations and to identify causes of errors and how to correct them

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