On/Off vs Modulating Electric Actuators: Which Control Type Do You Need?

Picking between on/off and modulating electric actuators depends on the valve's actual task. It is not just about the price tag. For example, a pipeline isolation valve might shift only once in a while. Meanwhile, a cooling-water valve might change positions all day long. Picking the incorrect control type leads to extra expenses. It can also create unstable regulation. Furthermore, it might cause too much motor cycling.

Understanding On/Off and Modulating Electric Actuator Control

The key difference is whether the actuator must repeatedly follow proportional position commands, rather than simply stop at intermediate points. On/off actuators are primarily designed for full-open and full-closed operation, while modulating actuators use position feedback to track intermediate setpoints accurately.

Factor	On/Off Control	Modulating Control
Target	Fully open or closed	Variable position
Command	Discrete open/close	Proportional setpoint
Feedback	Typically end-position status; optional continuous position feedback	Continuous position feedback for closed-loop positioning
Typical role	Isolation or switching	Process regulation

How an On/Off Electric Actuator Controls Valve Position

An on/off electric valve actuator gets a simple open or close signal. Then, it travels straight to that specific end point. Limit switches halt the motor at these fixed travel boundaries. They also give clear end-position feedback. This setup works perfectly for isolation and diversion. It is also great for planned switching tasks. However, it is not meant for constant tweaking. The actuator still requires enough torque to handle the valve's normal working conditions. This includes overcoming initial breakaway resistance.

How a Modulating Electric Actuator Provides Proportional Control

A modulating electric actuator accepts a proportional signal. It then moves the valve to a specific middle spot. Built-in feedback lets the controller see the difference between the requested target and the actual movement. This detail becomes very important when a PLC changes the valve opening. The PLC does this to control system pressure, flow rates, or temperature. You should not mix up position accuracy with flow accuracy. The unique traits of the valve also decide how an angle shift impacts the whole process.

Key Technical Differences Between On/Off and Modulating Actuators

EN 15714-2 Duty Classification: Class A vs Class C

EN 15714-2 distinguishes Class A full-stroke switching from Class C frequent intermediate positioning. Class B permits occasional positioning, while Class D covers continuous modulation. These are duty classifications, not simply control-signal labels. A 4–20 mA input does not by itself establish compliance with Class C. Buyers should confirm the required classification against the selected actuator’s specifications and qualification evidence.

Duty Cycle, Operating Frequency, and Motor Protection

Duty cycle describes permissible motor running time over a defined period; starts per hour also matter. In our Ulli range, AC-motor duty ratings include 80% at 50 and 100 Nm, approximately 60% at 250 Nm, and around 50% from 500 to 2,000 Nm. Digicon AC-motor models range from 50% to 80%, depending on size. For heavier cycling, our BLDC range supports 100% duty. Match the model to actual movement frequency and thermal load.

Control Signals and Feedback: 4–20 mA, 0–10 V, and Modbus

Basic on/off control normally relies on discrete commands. It uses simple end-position alerts. Proportional setups rely on signals like 4–20 mA or 0–10 V to set a target spot. Then, feedback lines report the real physical travel. Our Digicon setups also work with 2–10 V, 1–5 V, and RS-485 connections. Modbus serves as a digital communication protocol. Meanwhile, RS-485 acts as the physical electrical link. You should always verify protocol options first. Check controller matching before you finalize any network plans.

Which Electric Actuator Control Type Fits Your Application?

When On/Off Control Is Sufficient for Valve Isolation and Switching

A typical application for a water-distribution isolation valve is full-open or full-closed operation. These valves are used on HVAC shutoff pipes and backwash cycles of filters, for example. A quarter-turn electric actuator is often used to operate these types of ball or butterfly valves. Important are torque, turning angle, and mounting dimensions. The required action in case of a power failure has to be specified independently from the control mode. Typical electric actuators switch off and remain in the last position of operation. Fail-safe versions, such as the actuators of the SuperCap series by AOITEC, use stored energy to move the valve to a preselected open or closed position.

When Modulating Control Is Necessary for Flow, Pressure, or Temperature Regulation

Think about chilled-water temperature management. A central building system tweaks the valve position whenever cooling needs shift. Water-treatment dosing lines and process-flow loops often demand this same middle-ground movement. Picking the right device then relies on signal matching. It also depends on positioning habits and correction rates. A modulating actuator cannot repair bad loop tuning by itself. The main controller and the valve must operate smoothly together. This teamwork prevents shaky or erratic movements.

How Valve Characteristics Affect Modulating Performance

The valve opening percentage does not always match the actual flow percentage. A normal isolation ball valve might deliver terrible throttling results. In contrast, a proper V-port valve offers much finer fluid regulation. A butterfly valve's reaction also changes based on pressure drops and the working angle. You should review the valve’s flow traits carefully. Look at the allowed throttling range before you judge the actuator's success. Highly accurate travel cannot fix the problems of a poorly chosen valve.

AOITEC Ulli vs Digicon: Selecting the Right Quarter Turn Electric Actuator

Ulli Series: On/Off Electric Actuators for Reliable Switching

Here at AOITEC, we supply the Ulli series. It handles quarter-turn on/off tasks for ball and butterfly valves. The torque range spans from 50 to 6,000 Nm. It features standard ISO 5211 mounting bases. You can select male or female drive options. It also comes with strong IP68 protection. Power options include DC 24 V and multiple AC voltage levels. The Ulli line fits OEM skids and water networks perfectly. It is ideal for standard valve automation tasks. This is especially true when steady end-position control remains your top goal.

Digicon Series: Modulating Electric Actuators for Precise Valve Positioning

Our Digicon series spans from 50 to 6,000 Nm. It focuses on proportional quarter-turn control tasks. The internal smart module handles positioning directly. It does not need any external positioner device. The control inputs and position feedback lines make PLC connection simple. The Digicon series features a die-cast aluminum housing and an IP68-rated enclosure. Maintaining this protection requires proper installation and sealing, including the cable entries. When you write an electric valve actuator specification, check the feedback type first. Verify the duty needs and process habits. Do all of this before you pick a final torque rating.

Final Selection Checklist and Meet AOITEC at Valve World Düsseldorf 2026

Before you ask for a price quote, clearly define these items:

1. Valve type, required torque, stem drive, and ISO 5211 connection.

2. Switching or proportional control, plus anticipated starts per hour.

3. Power supply, command and feedback signals, ambient conditions.

4. Power-loss action and any commissioning requirements.

We can help match these inputs to Ulli on/off or Digicon modulating options. Contact AOITEC to discuss your application. We also plan to attend Valve World Expo Düsseldorf 2026, December 1–3, to meet valve and automation buyers.

FAQ

Q: What is the difference between an on/off electric actuator and a modulating electric actuator?

A: On/off devices travel between end positions. Modulating units accept intermediate setpoints, allowing a suitable valve to regulate process conditions.

Q: What control signals does a modulating electric actuator support?

A: The most common signals feature 4–20 mA and 0–10 V formats. The Digicon line provides several other signal choices as well. Please confirm your required interface during the ordering stage.

Q: What duty cycle should a quarter turn electric actuator have for frequent operation?

A: Choose by running time, starts per hour, and operating load. AOITEC offers model-dependent AC-motor duty ratings and 100%-duty BLDC options.

Q: Can a quarter-turn electric valve actuator regulate flow through a ball or butterfly valve?

A: Yes, it certainly can. The actuator must support proportional positioning first. Also, the chosen valve must be built for throttling under your specific working conditions.

Q: What are the top electric valve actuator manufacturers?

A: Leading electric valve actuator manufacturers include AUMA, Rotork, and Bernard Controls. AOITEC is also a manufacturer worth considering, offering on/off and modulating electric actuators for industrial valve automation.