Double-Acting Rotary Electropneumatic Positioner — 4-20 mA, IP66, Ex dIIB T6, Aluminum Body, as it does not require a microprocessor

Cematic's double-acting rotary electropneumatic positioner converts the 4-20 mA analog electrical signal from the control system into a proportional pneumatic pressure to position single-acting linear actuators. Unlike smart digital positioners, this model operates purely analogically, as it does not incorporate a microprocessor or HART communication.

Its operation is analog and direct. Unlike the single-acting type, the double-acting type controls the pressure in both actuator chambers. The input signal mechanically actuates the pneumatic pilot, therefore no additional electronic processing is required.

The Ex dIIB T6 certification — explosion-proof encapsulation — also enables it for installation in classified areas with Group IIB gases in Zones 1 and 2. Its aluminum body with IP66 protection, furthermore, guarantees durability in industrial environments with the presence of humidity and vapors.

Electropneumatic vs. smart — when this positioner is the correct specification when HART is not required

The selection between an analog electropneumatic positioner and a smart one depends on diagnostic, calibration, and cost requirements. The cases where the electropneumatic is the correct specification are described below, as not all projects require the functionality of the smart positioner:

• Processes where remote diagnostics or HART communication are not required — since the electropneumatic positioner covers the basic positioning function: When the process only needs the valve to be positioned proportionally to the 4-20 mA signal, the electropneumatic positioner is sufficient. The smart positioner with HART adds diagnostic functionalities that are not always necessary, therefore increasing the cost without providing benefit in those cases.
• Budget-restricted projects where basic functionality is sufficient, as the electropneumatic is lower cost: The electropneumatic positioner is lower cost than the smart one, as its analog design is simpler. It is the correct specification when the project budget does not justify the smart positioner and the required function is proportional positioning without remote diagnostics.
• Existing installations where the available signal is only 4-20 mA, as there is no fieldbus infrastructure: In many industrial installations, the control system only has a 4-20 mA analog signal without IO-Link or HART infrastructure. The electropneumatic positioner is, likewise, the correct option in those cases as it does not require a bus master or additional configuration.

Ex dIIB T6 — why encapsulation is different from intrinsic safety and when it is correct

The Ex dIIB T6 certification uses the concept of encapsulation: any arc or spark generated inside the positioner is contained within the housing and cannot ignite the external atmosphere. The characteristics of this certification are described below, as they define in which zones and for which gases it is the correct specification:

• Ex d — encapsulation that contains any internal spark, as it is the most common concept in industrial positioners: The aluminum casing seals the inside of the positioner and withstands any internal explosion. Consequently, an internal spark is contained and cannot ignite the external atmosphere. It is the correct concept in Zone 1 and Zone 2 for most industrial gases.
• Group IIC — suitable for hydrogen and acetylene, as they are the most demanding gases in the classification: Group IIC is the most demanding of the ATEX/IECEx classification. It covers Group IIA and IIB gases and, additionally, hydrogen and acetylene from Group IIC. Therefore, this positioner is the correct specification in processes with hydrogen where Group IIB positioners would be insufficient.
• Temperature class T6 (85°C) — for gases with low auto-ignition temperature: The T6 class guarantees that the surface temperature of the positioner does not exceed 85°C. It is more restrictive than T4 (135°C). Consequently, it covers gases with lower auto-ignition temperatures such as carbon disulfide and some organic solvents.

Technical specifications that define the application limits of the single-acting linear electropneumatic positioner

Electropneumatic positioner vs. smart positioner — comparative table to select the correct one according to the process

Main applications where the double-acting rotary electropneumatic positioner is the correct specification

• Control of globe valves in flow, pressure, or temperature regulation processes: The positioner converts the 4-20 mA signal from the PID controller into the proportional position of the valve's rotary actuator. It is, likewise, the correct specification in rotary valve control loops where continuous positioning without remote diagnostics is required.

Its lower cost compared to the smart rotary positioner makes it suitable for installations with many ball or butterfly valves where budget is a relevant factor.

• Chemical and petrochemical industry with processes handling hydrogen or other Group IIC gases: The EX ia IIC T4 Ga certification is the correct specification in process units with hydrogen, as Group IIB positioners do not cover that gas. The concept of intrinsic safety is, likewise, admissible in Zone 0 where EX db encapsulation is not enabled.

Applications in energy, water, and modernization where the rotary electropneumatic positioner also meets the requirement

• Power generation and steam systems where precise positioning is critical: In power plants, this positioner controls globe valves in steam lines, boiler water, and process fluids with a direct 4-20 mA signal from the DCS. Its analog operation without a microprocessor also reduces the risk of electronic failure in high-temperature environments.
• Water treatment and dosing systems where the analog signal is the standard: In water treatment plants with control systems that only have a 4-20 mA analog signal, this positioner integrates directly without the need for an additional bus master. It is, therefore, the simplest and lowest-cost option in these installations.
• Modernization of manual valves to proportional control in installations with existing 4-20 mA signal: When an installation has 4-20 mA wiring available and needs to convert manual valves to proportional control, this positioner is the lowest-cost and simplest option. Finally, it does not require fieldbus infrastructure or an IO-Link master for its integration.

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Technical Data Sheet