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EMCO 4-Electrode Conductivity Sensor Series 621

EMCO 4-Electrode Conductivity Sensor Series 621



The EMCO Conductivity Sensor Series 621 is designed to monitor very high and very low conductivity in process solutions.


Power plants, conventional and nuclear. Pulp & Paper. Oil & Gas industry.
General food and Beverage industries. And other liquid handling industries.


The EMCO 4-Electrode Conductivity Sensor Series 621 principle employs two current and two voltage electrodes.
The two current electrodes apply an alternating voltage and induce a constant current loop.
The two voltage electrodes measure a voltage drop depending on the conductivity of the fluid.
The alternation eliminates the effect of polarization.
4 electrode sensors are therefore not sensitive to contamination and have a much wider measurement range. The electrodes are external for use in larger pipes and for lower conductivity ranges. Series 611 is for smaller pipes.

Temperature Compensation

The ionic activities increase with increasing temperature. In average the conductivity changes 2%/°C. Conductivity measurements are all referred to reference temperature of 25 °C. In industrial processes the temperature often changes therefore temperature compensation is necessary. The built in temperature sensor is very accurate with a low response time.

Our many years in instrument design guarantees a roughed design, but still allows the possibility to solve customers´ special requirements. A selection of electrode and sensors element materials is available to suit the specific application.

Principle of Measurement

Electrical conductivity is the ability of a liquid to carry a current.
The conductivity is equal to the conductance of the liquid times the cell constant.
The conductance is the reciprocal of the electrical resistance of the liquid measured.
The cell constant is equal to the distance between the electrodes divided by the effective area of the electrodes.

Cell Constant

The cell constant is equal to the distance in cm between the electrodes divided by the effective area in cm² of the electrodes.
The applicable value of the cell constant depends on the conductivity of the solution being measured. Low conductivity requires low cell constant and high conductivity requires high cell constant.

Factory determined cell constant ensures highest accuracy. The cell constant is marked on the sensor. The dedicated analyzer is programmed with this specific cell constant ensuring the highest accuracy.


Easy to install | Applicable for high temperature and pressure | Rugged design | Wide selection of materials and mounting options | Resistant to scaling.

Technical Specification

Measuring range  0,05 μS/cm to 1000 mS/cm 
Material. electrodes  Stainless steel AISI 316, other materials on request 
Material. sensor body  Stainless steel AISI 316, 22 Cr duplex, 25 Cr duplex,
Hastelloy C-276, Monel, Titanium, FDA approved.
Other materials on request 
Material. Electrode holder  PTFE 
Process connection  1 ¼” internal thread BSP or NPT, 1” external thread BSP or NPT 
Installation lengths 120 mm (standard), 350 to 3500 mm see coding for selection 
Pressure Max 30 bar-g, higher pressure on request 
Temperature Max 200oC
Temperature element  Pt1000 Class A 
Cell constant individually determined, value is marked on sensor body
Uncertainty 1% per decade 
Protection class  IP65 
Electrical connection 9 pole connector   


The sensors can be calibrated in one or several points documented at reference temperature of 25°C


Dimensional drawing
Material certificate according to EN 10204-3.1
Pressure test certificate
Calibration certificate
Instruction manual

Overall Dimensions



With our fully equipped machine shop including welding EMCO Controls can supply mechanical parts including flow tubes, by-pass systems etc

Quality Assurance

EMCO Controls is certified according to ISO 9001- 2008,
Pressure Equipment Directive PED Module H,
and welding quality certificate to EN 3834-2.

Sensor Coding