What is Modulating Actuator?
An electric actuator is the mother device of valve automation. It transforms electrically produced high speed low rotary motor torque into low speed high rotary torque. There is an internal system for modulating electric actuators. It helps to position the output shaft to an input control signal. Modulating actuators don’t need to travel the full span from open to close in one movement, and it’s not like on-off electric actuators. These actuators move only according to the change of the input control signal. The input signal fixes the proportional positioning. For 0-10V, 0V is closed, and 10V is open. 5V is 50% open.
The positioner continuously observes and compares the input control signal, and it is doing proportionately with the physical location of the output drive. If any exception is found, the positioner fixes the direction and run time of the actuator motor to withdraw the exception.
The standard analog control input signal is 0-10VDC, and the standard current rating is 4 to 20mA. There are a few modulating electric actuators that provide an output signal also. Here the attained position is compared to the wanted position.
A modulating control valve is an automated valve. It is used to control the amount of flow in a system. There are actuators on these valves which use feedback and control signals. Actuators help to open and close the valve accurately. A control signal is sent to the actuator to train it on how far to raise or turn the medium. The control signal is in the form of air pressure or electrical voltage. For example, a 3 to 15 psi pneumatic signal causes the actuator to fully closed the valve at three psi or lower. Again, a 3 to 15 psi pneumatic signal occurs for the actuator to open it at 15 psi or above. A 0 to 10-voltage DC electric signal causes the actuator to close the valve at 0 voltage DC completely. Similarly, completely open it at ten voltage DC or above.
Usually, a flow meter downstream is used from the valve. It measures the flow rate and refers that data to a control computer. The computer then applies the proper logic. This logic can generate the signal. The signal adjusts the valve in either direction until the wanted flow rate is met.
Pros & Cons of Modulating Actuator
- Precision: An actuator can precisely control the flow by adjusting the amount of flow passing through the valve. This amount may change depending on the requirement for the application.
- Efficiency: The actuator consumes less energy than frequent on/off action.
- Remote Control: Modulating Actuator provides remote and automated control facilities.
- The actuator generates heat and requires frequent & scheduled maintenance.
- Time-consuming related to a hydraulic or pneumatic actuator.
Uses of Modulating Actuators with 0 to 10 Volt
- HVAC systems
- Power plants
- Steam supply lines
- Wastewater treatment plants
- Automation industry
- Irrigation systems
Technical Data Specifications of an Ideal Modulating Actuator
|Nominal Voltage||AC/DC 24 V|
|Modulating standard control signal||DC 0-10 V|
|Position feedback||DC 2-10 V|
|Position accuracy||+/- 5%|
|Power consumption||In operation: 1 W; At rest: 0.2 W; For wire sizing: 2 VA|
|Control||Control signal : DC 0-10 V,|
|Typical input impedance||100 kΩ|
|Direction of rotation||Reversible|
|Angle of rotation||Maximum 95 degree|
|Running time||150 s|
|Sound power level||Maximum 35 dB|
Modulating Actuator Function
We can monitor the physical position of the modulating electric actuator’s output shaft. It has two different ways. One is using a mechanical device. This mechanical device is a potentiometer. It is run by a gear connected to the output shaft. Another way is sensing the shaft position digitally. In past years, the mechanical potentiometer system was the only choice. Even this system is performing well. We should also count potentiometer failure in this system.
Digital magnetic position sensing is an excellent invention for determining the output shaft position. It happens with hall effect sensors. A magnet is set to the modulating actuator’s output shaft. A digital encoder is also used. This process is very precise & digital.