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LDL sensors for phase separation and CIP monitoring – a new approach

Introducing the conductivity sensors from ifm


Reduce inaccuracies associated with a time-based cleaning process.
Measurement at each piece of equipment or process segment verifies the product and confirms cleaning or rinsing has been properly completed. Eliminating a time-based process control ensures that you run the cleaning and rinsing cycles only as long as needed.
Achieve higher safety margin with feedback during recipe changes and cleaning cycles.
Without a way of measuring concentration of chemicals in a CIP system, a purely time-based method is used. This assumes the entire system is set with the correct chemical concentrations and the wash cycle is run for sufficient time.
Cycle time usually includes some safety margin to ensure complete cleaning.
Because cycle time is likely longer than necessary, more energy is used to pump and heat the fluids and more resources (cleaning agents, water, etc.) is used throughout the cycle.
Improve process performance with flexible measurement points.
More measurement points increases your ability to segment and refine the control of your process. These additional points provide you with the information to reduce cycle time, usage of water / chemicals, and decrease energy consumption.
Compact, high-quality sensor design prevents failures and unplanned downtime.
The LDL family reduces failures by providing an all-in-one transmitter rated IP68/IP69K. It consists of a one-piece stainless steel housing, machined PEEK measuring tip with no terminal chambers or cable cord grips that are often a point of water ingress for sensors installed in washdown environments.
Simplify your installation and commissioning processes with compact plug and play sensors.
Many conductivity sensors on the market are big and bulky or have probes with separate evaluation units requiring matching and calibration in the field. The compact size of the LDL series allows it to fit easily on small systems/skids and reduces mechanical stress on your piping system. The standard 4-pin M12 electrical connector eliminates the need to wire terminal chambers, and since the LDL is an all-in-one transmitter, no field calibration is required – it is virtually a plug-and-play device.
Factory Calibration Certificates can be downloaded at no cost from our website with the sensor serial number.

With IO-Link, the LDL family can provide:

  • Conductivity and temperature value over a single wire
  • High measurement resolution without scaling
  • On-the-fly recipe changes and device adjustment
  • Current device status
  • Operating hours histogram
  • Internal memory for min and max conductivity / temperature
  • Automatic device replacement

Using IO-Link, the resolution of the conductivity value is the same throughout the measuring range. This is especially important when using the inductive (toroidal) version. A typical CIP process uses chemicals with high conductivity and rinse water with low conductivity. When using an analogue output, the signal is spread out over a greater range, reducing the ability to detect small changes in conductivity. This can lead to residual amounts of chemicals going undetected in rinse water or products.


Comparison of resolution of IO-Link and analogue signals

Measuring range


PLC analogue input card

(12 bits)

IO-Link *
0...500 1µS/cm 1µS/cm
0...5,000 2µS/cm
0...15,000 4 µS/cm
0...100,000 25 µS/cm
0...500,000 122 µS/cm
0...1,000,000 244 µS/cm

* LDL100 measuring range is limited to 15,000 µS/cm.


CIP (Clean-in-Place)

To remain competitive, it is important to minimise production downtime without compromising the safety and quality of the product. Monitor wash fluid concentration and completed chemical flush out of the line.

Use case: CIP process in dairy

A major global dairy company (with plants around the world) was experiencing challenges with its liquid analytical systems, particularly related to CIP.

  • 50% failure rate on sensors each year -- approximately €1000 per sensor
  • Cost of plant downtime -- up to €90,000 per hour

The company implemented ifm’s LDL200. Instead of two sensors (one for low-conductivity rinse water and one for high-conductivity cleaning agents), the LDL200 can measure the entire range of fluids.

  • Lower initial cost
  • Less installation space required
  • Reduced maintenance and training requirements
  • No loss of accuracy due to resolution constraints

Verification of proper CIP and rinsing was absolutely required to ensure high quality of products leaving the plants.

Phase shift/product verification

Regardless of opacity, conductivity can be used in some applications where turbidity will not work, and can detect the interface between rinse water, caustic or acidic CIP solution, and product. Only a measurable difference in the media’s conductivity is required.

(1. milk, 2. rinse, 3. caustic , 4. acid)

Media used in CIP systems have a repeatable difference in conductivity.

Leak detection

Heat exchangers use one fluid to heat or cool another fluid and a conductivity sensor on the outlet or in the condenser hotwell is an easy way to detect leaks.

This also ensures the fluids have not mixed and improves the efficiency and quality of the heating / cooling process.

Water quality

Raw water from lakes, rivers or taps usually contains contaminants that can cause scaling and corrosion in industrial plant equipment, particularly heat exchangers, cooling towers and boilers. Because conductivity is a measure of total ion concentration, it is ideal for monitoring demineralizer performance. Ensure your process starts with the correct water quality and determine if it is reusable in another part of the plant or process. You can reduce your overall water consumption if your final rinse water can be reused as pre-rinse on the next cycle.


The concentration of salt (NaCl) in water can be monitored easily using conductivity. As few as 5 grains of salt produce a measurable difference in conductivity.

Monitor dissolved ionic solids in drinking water desalination plants. Monitor salt water concentration to increase the cooling power of water (lower the freezing point) and to ensure high quality of brine solution used for various foods.

Use case: Salinity of cooling water

A large processing facility was looking for a solution to automate their cooling water tanks, which consist of a saturated salt solution. The salt solution was used to lower the temperature of their cooling water beyond what is possible with standard water, and since the cooling water is in direct contact with the food product, they needed something safe.

Their previous solution was to periodically take manual salometer readings of each cooling water tank and adjust the salt concentration as required. This was a very labour-intensive process as they have multiple tanks spread out across the facility that trend differently based on the packaged meat products they are cooling. The adjustment of the salt concentration was also manual and dependent on employees carefully following labour-intensive processes.

The most critical impact of an incorrect measurement or low concentration is that the cooling water tanks and system could freeze solid. The result of this was a downed line and hours of lost production until the tank were thawed. The lesser but still important effect was product quality. The brine solution is also used to impart flavour into certain products and fluctuating concentration levels result in variable taste profiles. Using too much salt is a waste of resources and eventually can build up causing blockages within the system.


Conductivity measures how well a substance conducts an electric current. It is influenced by the quantity of free ions (salts, acids, alkalis) in the medium and by the temperature of the medium: the more free ions, the higher the conductivity. A conductivity sensor typically consists of two metal plates in contact with the medium. If two electrodes are immersed in a conductive liquid and a voltage is applied to these two electrodes, a current will flow.

The positively charged ions (cations) move to the negatively charged electrode, and the negatively charged ions (anions) move to the positively charged electrode. The more free ions in the medium and the higher the electrical conductivity of the medium, the higher is the current.

The SI unit for conductivity is Siemens per metre (S/m). The following figure shows the conductivity values for some common media.

There are two methods to measure the conductivity: galvanically and inductively. The choice depends on the conductivity of the medium, the corrosiveness of the liquid and the suspended solids content.

Galvanic conductivity sensors (LDL1xx)

The galvanic conductivity sensor from ifm has two metal electrodes like other measuring conductivity sensors. The difference in our design is that the sensor housing and metal tube serve as the first electrode and the metal tip of the sensor serves as the second electrode.

Voltage is applied between the sensor tip and the housing screw connection and the current flow is measured.

Inductive conductivity sensors (LDL2xx)

An inductive conductivity sensor consists of two metal coils wound with wire and enclosed in a plastic body (PEEK is used for ifm products). The first coil (transmitter coil) generates an electrical voltage in the liquid. Depending on the conductivity of the medium, an alternating current is generated. The latter generates an alternating magnetic field in the second coil (receiving coil) that is proportional to the conductivity of the medium.

Inductive conductivity measurement has several advantages:

  • High resistance to corrosion thanks to the PEEK tip.
  • Insensitive to solids in the medium as long as the measuring channel is not clogged.
  • No influence by media with high conductivity.

Influence of temperature

The conductivity of a material is particularly dependent on temperature - approximately 1...5% per °C. All conductivity sensors have a built-in temperature measurement to compensate for temperature changes in the medium.

LDL sensors – further features

Cord grips and terminal chambers are sources of ingress. This is often a weak point for sensors installed in washdown environments. The LDL family reduces failures by providing an all-in-one transmitter rated IP68/IP69K. It consists of a one-piece stainless steel housing, machined PEEK measuring tip with no terminal chambers or cable cord grips.

All LDL conductivity sensors come factory calibrated and ready to use out-of-the-box. Factory Calibration Certificates can be downloaded at no cost from our website with the sensor serial number.

Using IO-Link, the sensors can also be field calibrated against a standard or reference solution using the Calibration Gain (CGA) parameter.

Product selector

ifm offers two versions of the LDL family:

  • LDL100 with a measuring range of 100µS/cm…15mS/cm. Media with a conductivity level higher than 15mS/cm cannot be measured, but the sensor can be used to differentiate them from media within the measuring range.
  • LDL2xxwith a measuring range of 100µS/cm…1S/cm.

Selector by media / conductivity value

1. Conductivity (µS/cm): 2. Ultra-pure water, 3. Pure water, 4. Service water, 5. Drinking water, 6. Beer, 7. Milk, 8. Fruit juice, 9. Phosphoric acid (1 %), 10. Sodium hydroxide (1 %), 11. Sulfuric acid (1 %), 12. Hydrochloric acid (1 %), 13. Sodium hydroxide (5 %)




Media transition measurement (e.g. rinse water / product)
Product differentiation / verification
Leak detection (e.g. heat exchangers)
Water quality (above 100 µS / cm)
CIP chemical concentration  

Installation conditions

For proper operation, some guidelines must be followed.


Preferable mounting is just before or in a vertical pipe with flow going up to ensure a full pipe. When installed in a horizontal pipe, install the sensor at a maximum of 45° from horizontal to avoid the influence of air bubbles or deposits.

The measurement channel of the LDL2xx must be installed parallel to the direction of flow. An alignment mark is laser etched on the body of the sensor indicating the correct orientation in the pipe.

Pipe size / recommended fittings

Pipe size


1" / DN25

Process adapter
Not recommended Not recommended
1.5" / DN38
Welding adapter


Process adapter
Not recommended Not recommended
≥2" / DN50

Process adapter

Clamp adapter
E33213 Milk pipe adapter


Welding adapter