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Intelligent Transmitter for Electrodeless Conductivity Measurements with HART Communication Protocol Model 876EC

876ec intellegent transmitter for electrodeless conductivity measurements with hart

Manufactured byfoxboro

The Foxboro® brand Model 876EC is a 2-wire loop powered intelligent transmitter that, when used with appropriate electrochemical sensors, provides measurement, local display, and transmission of electrodeless conductivity. The transmitter outputs a HART digital signal and a 4 to 20 mA analog output.


  • 4 to 20 mA output with a HART(1) digital signal.
  • Temperature prediction(2)
  • Remote configuration/calibration with the HART Communicator or PC-based Configurator.
  • Local configuration with the keypad on the integral local human interface.
  • LCD indicator can display either one, two, or three measurement variables.
  • Fault isolation to transmitter or sensor. Continuous transmitter/sensor diagnostics.
  • Temperature compensation and concentration curves.
  • Approved/Certified as intrinsically safe device for use in hazardous area locations.
  • FDT certified DTM (Device Type Manager).
  • Wide measurement range.
  • Two levels of passcode protection provided.
  • Compatible with Foxboro 871EC, 871FT, EP307B, EP307G, and FT10 Series electrodeless conductivity sensors.
  • Complies with applicable NAMUR standards, and EMC directive 2004/108/EC.
  • Enclosure meets IP66 and NEMA 4X ratings.
  • Output Hold.


This transmitter can be configured to measure in conductivity units (μS/m, μS/cm, mS/m, mS/cm, or S/m), or one of a host of chemical concentration units such as percent (%) by weight, grams per litre (g/L), parts per million (ppm), and parts per thousand (ppt). A series of preprogrammed temperature and percent chemical concentration curves are available as a standard feature. User programmable curves may also be used for special applications such as uncommon chemicals, proprietary processes, or nonbinary solutions.


The 876EC Transmitter is designed for compliance with FM, CSA, ATEX, and IECEx standards for intrinsically safe and non incendive apparatus in hazardous area locations. Refer to the Electrical Safety Specifications section.


For a Foxboro sensor, a proprietary mathematical algorithm is applied to accelerate the sensor’s response to changes in the process temperature. This reduces errors that may appear in the compensated measurements when the process temperature changes rapidly.


This transmitter provides efficient integration of measurements into HART process control schemes. It operates by using a bidirectional digital signal superimposed on the 4 to 20mA analog output. Remote communication of digital values plus status and configuration information can be achieved via HART communication protocol. Configurations used with this HART version are: The HART Communicator (users having HART Communicator for other devices can have them upgraded with Foxboro Device Descriptors (DDs) to accommodate this transmitter). The local Human Interface (see upcoming section). A PC-based configurator (FDT). A Distributed Control System (DCS). With HART, digital multidropping is permitted. This is the connection of several transmitters to a single communications line. Multiple transmitters can be connected on a single twisted pair of wires. 


This unique feature allows you to preconfigure the transmitter for up to three different applications. Each application may have its own display format, temperature compensation curve, chemical concentration curve (if applicable), and output configuration. Each application is assigned a number, for example, “Application 1”, “Application 2”, or “Application 3”. If you wish to switch from one application to another, you can simply change one parameter in the configuration menu and the entire application set switches in automatically. This is a powerful feature for users who frequently change between a handful of common, or even custom, recipes.


A useful extension to the multi application feature is an auto-switching capability between either two or three applications. User-programmable switch limits determine when the transmitter auto-switches from Application 1 to Application 2, then again from Application 2 to Application 3. Similarly, the transmitter auto-switches in descending fashion depending on the program set by the user. Because each of the applications (three maximum) is individually configured, calibration constants are stored in memory and invoked as the application is retrieved. Thus the transmitter can switch from a wide range conductivity application to a very sensitive one (e.g., Rinse, Product, and CIP) without the need to recalibrate the system for the new range. This results in tremendous time savings for operators, and eliminates common sources of error in critical applications.


Highly accurate measurements are provided by the combination of the 876EC Transmitter and patented 871EC Sensors. Refer to Table 1 on page 10, Table 2 on page 11, and Table 3 on page 14, for a listing of the wide variety of conductivity ranges available. The transmitter delivers a high sensitivity conductivity system for applications such as steam condensate or boiler blowdown. Measurement display formats as low as 9.999 μS/cm can be accommodated. However, the analyzer is also capable of measuring as high as 2000 mS/cm with numerous intermediate measurement display choices, thus assuring full compatibility with all applications.


Configuring an electrochemical transmitter involves the setting of many parameters specific for the application. For example, measurement, sensor configuration, temperature compensation, output, chemical composition, and damping are just a few of the parameters that can be configured. In some cases, you may wish to employ the transmitter for more than one application (at different times). Rather than having to change several parameters, the Model 876EC allows you to save up to two unique and complete configuration profiles, even when they contain multiple applications. Each profile can have up to 3 applications. Either of these two profiles can be restored at any time to facilitate a quick and easy change of the transmitter to a pre-saved configuration. In addition to the two user profiles, the transmitter also includes a “factory default” configuration which allows you to return the transmitter to its original factory configuration at any time.


Using the status key, you can access all the information necessary to assess the performance of the measurement loop. Among the parameters are: Solution Temperature, Absolute Measurement, Compensated Measurement, Chemical Concentration, Measurement Status, Date of Last Calibration


These functions include View Faults, Suspend Faults, Resume Faults, and View History. Typical faults include: Measurement Overrange and Underrange Compensation Overrange and Underrange Analog Output Overrange and Underrange Calibration Required Liquid Leakage into Sensor Body ATC Short and ATC Open The user can enable or disable any of the listed faults. Fault status is displayed in the main Diagnostic Menu. If there are no faults, then “No Active Faults” will be displayed. The user can suspend active faults from the measurement status for one hour, and can resume faults at any time.


The history log can be viewed and cleared by the user, and can be viewed using any of four filters: an error selection, an operational selection, a calibration selection, and an all history selection. The history log includes all faults, power restore, entries and exits from configuration, calibration, and Hold, and faults that have been temporarily suspended.


Invensys is the world leader in electrodeless conductivity sensor technology and product breadth. Invensys offers both insertion/submersion sensors, the 871EC Series; and revolutionary flow-through sensors, the 871FT and the FT10 Series. These sensors are offered in a multitude of sizes, materials, geometries, and mounting configurations to satisfy the majority of applications in process industries. Different sensor form factors and construction techniques result in different sensor cell factors, which affect the sensitivity and range of a particular conductivity loop. To simplify the sensor compatibility process, the analyzer provides menu selections for each type of 871EC, 871FT, and FT10 sensor, as well as custom cell factors for optimization of special sensors. In addition, a selection of three different temperature compensator inputs (100 ohm platinum RTD, 1000 ohm platinum RTD, and 100 k ohm thermistor), ensures compatibility with standard temperature sensors, high temperature sensors, and sensors of a specialized nature. Refer to Figure 1 for FT10 non-invasive, nonmetallic flow-through sensors, and Figure 2 for 871FT flow-through sensors and 871EC Series sensors.


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