What is the meaning of the following Terms:

1) Servo Valve (Is a servo valve same as an ON-OFF Two Position Valve or is it a Continuous Valve)

2) Servo Mechanism (Does it in a layman term mean any kind of a position control system/mechanism?)

3) Servo Motor (Is a stepper motor a servo motor? Is a continuous DC/AC motor a servo motor?)

4) Can a simple pneumatic Control Valve positioning loop be called as a servo system?

Which of the following case is a Servo System?

A Hydraulic Flue Gas Flow Diverter (FGFD) System is installed in the downstream of a Gas Turbine which permits the flow of Flue to the Downstream HRSG (Heat Recovery Steam Generator)... In our Plant two philosophies are used to control the postion of the FGFD...

Case 1: An ON-OFF Direction Control SOV is used to open or close the damper... The SOV's opening time is controlled by a PID PWM controller...

Case 2: In the second FGFD System, the FGFD position is controlled using a Servo-Hydraulic Valve that is continuous in nature...

Which of the above two systems can be called a true servo system?

Can the ON-OFF valve in the "Case 1" be called as a servo valve or is it a proportional valve?

Regards
Grishma

 

Hello Grishma;

From the following excerpt (Wikipedia) you can deduce most of your answers (ex: case1 cannot be called a servo application):

Servomechanism

Small R/C servo mechanism
1. electric motor
2. position feedback potentiometer
3. reduction gear
4. actuator armA servomechanism, usually shortened to just servo, is a device used to provide mechanical control at a distance. For example, a servo can be used at a remote location to proportionally follow the angular position of a control knob. The connection between the two is not mechanical, but electrical or wireless, for example.

The most common type of servo is that mentioned, which gives positional control. Servos are commonly electrical or partially electronic in nature, using an electric motor as the primary means of creating mechanical force, though other types that use hydraulics, pneumatics or magnetic principles are available. Usually, servos operate on the principle of negative feedback, where the control input is compared to the actual position of the mechanical system as measured by some sort of transducer at the output. Any difference between the actual and wanted values (an "error signal") is amplified and used to drive the system in the direction necessary to reduce or eliminate the error. A whole science of this type of system has been developed, known as control theory.

Servos are found in many applications. They operate the throttle of engines that use a cruise control. CNC machines use servos to make the motion axes of a machine tool follow the desired tool path. Fly-by-wire systems in aircraft use servos to actuate the control surfaces that control the aircraft. Radio-controlled airplanes use servos for the same purpose. Many autofocus cameras also use a servomechanism to accurately move the focus.

Typical servos give a rotary (angular) output, though linear types are common too, using a screw thread to give linear motion, or using a linear motor.

Another device commonly referred to as a servo is used in automobiles to amplify the steering or braking force applied by the driver. In this form this device is not a true servo, but rather a mechanical amplifier.

Also in the industrial machines servos are used to perform complex motion.

5 Servomechanism

A servomechanism, usually shortened to just servo, is a device used to provide mechanical control at a distance. For example, a servo can be used at a remote location to proportionally follow the angular position of a control knob. The connection between the two is not mechanical, but electrical or wireless, for example.
The most common type of servo is that mentioned, which gives positional control. Servos are commonly electrical or partially electronic in nature, using an electric motor as the primary means of creating mechanical force, though other types that use hydraulics, pneumatics or magnetic principles are available. Usually, servos operate on the principle of negative feedback, where the control input is compared to the actual position of the mechanical system as measured by some sort of transducer at the output. Any difference between the actual and wanted values (an "error signal") is amplified and used to drive the system in the direction necessary to reduce or eliminate the error. A whole science of this type of system has been developed, known as control theory.
Servos are found in many applications. They operate the throttle of engines that use a cruise control. CNC machines use servos to make the motion axes of a machine tool follow the desired tool path. Fly-by-wire systems in aircraft use servos to actuate the control surfaces that control the aircraft. Radio-controlled airplanes use servos for the same purpose. Many autofocus cameras also use a servomechanism to accurately move the focus.
Typical servos give a rotary (angular) output, though linear types are common too, using a screw thread to give linear motion, or using a linear motor.
Another device commonly referred to as a servo is used in automobiles to amplify the steering or braking force applied by the driver. In this form this device is not a true servo, but rather a mechanical amplifier.
Also in the industrial machines servos are used to perform complex motion.

Hope this helps,
Daniel Chartier