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FUNCTION :
Many modern installations in automated process control applications require the use of electronic controllers to provide electrical signal to position the final control element in the proportionate manner. In the closed loop system the positioner is usually located in between controller and final control element. Generally the final control element is normally a pneumatically driven power device e.g. control valve |
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PRINCIPLE OF OPERATION :
The Electropneumatic positioner receives an electrical signal from the electronic controller. The unit can accept it in 4 different forms - 1) 0 - 20 mA DC 2) 4 - 20 mA DC 3) 0-1V DC 4) 0 - 10 V DC. With this input, the unit regulates the high pressure air supply to the final control element to give a corresponding displacement. This position control unit operates on the pulse width modulation principle. The input signal is conditioned and given to a precision instrument amplifier. Also the signal from the feedback element is conditioned and given to the precision instrument amplifier. Depending on the difference of these values (Desired position and Actual position) the relays are driven by pulse width modulation to operate the solenoid valves. This inturn changes the position of final control element till the desired position is achieved. The unit can be arranged to give either linear or logarithmic relationship between the control signal and Actuator position. The actuator can be arranged so that increase in electrical signal moves the actuator in either direction. The direction of movement in relation to the control signal can be easily reversed on site by changing the connections. No extra material is required for the same. Optional Indicator can be provided to indicate the position of final control element. |
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TECHNICAL SPECIFICATIONS : |
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| 1. Input
Signal |
: |
a) 0 - 20 mA DC
b) 4 - 20 mA DC
c) 0 - 01 V DC
d) 0 - 10 V DC |
| 2. Pneumatic Supply |
: |
Max 10 bar. |
| 3. Electrical Supply |
: |
230 V AC, 50 Hz /
50 W Max. at time of correction |
| 4. I/P
Impedance |
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750
ohms |
| 5. Effect of Supply variation |
: |
Nil |
| 6.Standard stroke |
:
:
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90 Degree Rotary
Linear Stroke
Both Adjustable |
| 7. Air Supply Connection |
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1/4" NPT |
| 8. Positional Effect |
: |
Nil, Can be mounted in any direction. |
| 9. Repeatability |
: |
1% of Span
(Travel) |
| 10. Linearity |
: |
1% of Span
(Travel) |
| 11. Hysterisis |
: |
1% of Span
(Travel) |
| 12. Deadband |
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2% of input Span (can be adjusted to 1%) |
| 13. Temp |
: |
5°Cto60°C |
| 14. Response time |
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Function of air consumption of final control element.
(Max one sec for all normal size actuation) |
| 15. Physical
dimension |
: |
120 x
200 x 75 mm |
Unless otherwise stated in order, the unit is adjusted for
4 - 20 mA DC input signal. |
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Useful for double acting or single acting Actuators The Electro Pneumatic Positioner is a unit which, when used on either ROTARY ACTUATOR, standard or thrust CYLINDERS, on CONTROL VALVES comprises Electro pneumatic position servo. The final control element can be moved to a desired position by means of a high pressure air supply providing the necessary power and speed of operation.
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SALIENT FEATURES :
Useful for double acting or single acting Actuators
/ cylinders.
Can be made Direct or Reverse acting.
Performance does not have any effect due to vibration.
Allows use of reliable, low cost, fast acting pneumatic actuators in
electronic control system.
Positioner is capable of giving 100% stroke for
40% input signal or 40% stroke for 100% input signal
Positive Mechanical feedback provides accurate
final control element movement for each value of
input signal.
In a balance condition the unit does not consume
air supply. Air is used only during operation the
electrical consumption of the unit is also
negligible.
The electronic control unit is same for all types of
actuating devices. Only the type of feedback element
changes as per final control element.
The electronic control unit can also be useful for
electrical actuators with some external
modifications. |
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