With the wide application of pneumatic valves, the technology of pneumatic actuators is getting better and better. The gap between domestic pneumatic actuators and imported pneumatic actuators is getting smaller and smaller, and the types are also increasing. Now the pneumatic actuators are inspected. The method is as follows:
a) verification preparation and visual inspection
1 All test instruments must be warmed up for 30 minutes in advance.
2 Test gas source pressure should meet 0.6±0.1Mpa
3 The appearance of the actuator is not obviously damaged, and the air guiding copper tube has no obvious scar and is firmly assembled.
4 The position transmitter connection screw length must meet the technical requirements of the type of actuator to be inspected; the plane formed by the connecting rod and the connecting screw fastened on the transmitter shaft should be perpendicular to the horizontal plane.
b) Inspection standards and methods
1 Fix the pneumatic actuator on the calibration table, connect the air source, control air source and displacement detection link respectively; adjust the instrument on the calibration table accurately.
2 Mechanical zero calibration: input 4mA current signal (0%), control gas signal should be 0.02Mpa, then the cylinder piston stroke should be zero; if it is not zero, adjust the zero point by adjusting the nut on the zero adjustment screw (zero point) High tightening nut); zero and span need to be adjusted repeatedly; zero error is ≤1%.
3 Mechanical full-scale calibration: input 20mA current signal (100%), control gas signal should be 0.10Mpa, then the cylinder piston stroke should be the upper limit; if it is not the upper limit, you can adjust the tension of the tension spring by the range Adjust the range (the range is small, the tension spring is loose, the range is large and the tension spring is large); the zero point and the range need to be adjusted repeatedly; the full scale error is ≤1%.
4 Mechanical range midpoint positioning: After zero point and span calibration, input 12mA current signal (50%, 0.06Mpa), adjust the position of the position transmitter connecting rod so that it is kept perpendicular to the horizontal plane at this point.
5 Full-stroke deviation calibration: input control gas signal 0.02Mpa (0%), then gradually increase the input signal 0.036 Mpa (20%), 0.052 Mpa (20%), 0.068 Mpa (60%), 0.084 Mpa (80%), 0.1 Mpa (100%), the cylinder piston is completely stroked, and the deviation of each point is ≤1.5%.
6, nonlinear deviation test: input control gas signal 0.02Mpa (0%), then gradually increase the input signal until 0.10Mpa (100%), then reduce the signal to 0.02Mpa (0%), so that the actuator goes completely And record the stroke value corresponding to each increase and decrease of the signal pressure of 0.008 Upa, and the nonlinear deviation between the actual pressure ┠stroke relationship and the theoretical value is ≤ 1%.
7 Positive and negative stroke variation test: The same as the nonlinear deviation test method, in the actual positive and negative pressure ┠stroke relationship, the difference between the positive and negative stroke values ​​of the cylinder piston at the same air pressure value is ≤1%.
8 Sensitivity test: increase and decrease the air pressure at the signal pressures of 0.03, 0.06, and 0.09Mpa respectively, and test the signal pressure change value required when the piston rod of the cylinder starts to move 0.1mm, and the large change of zui is ≤0.2%.
9. Sealing test of piston cylinder: Connect the pressure of 0.5 Mpa into any air chamber of the cylinder, and then cut off the air source. Within 10 minutes, the pressure drop in the cylinder should not exceed 0.01 Mpa.
10 Position transmitter electrical zero detection: open the position transmitter top cover, connect the wires; input 12mA current signal (0.06 Mpa), then adjust the circular eccentric inside the transmitter to make the black line and line above it The white line above the board is aligned; then input 4mA current (0.02 Mpa), then adjust the zero potentiometer in the transmitter to make the output current 4mA; the electrical zero error should be ≤1%.
11 Position transmitter electrical full-scale detection: input 20mA current signal (0.1 Mpa), at this time, adjust the transmitter internal range potentiometer to make the output current 20mA; electrical full-scale error should be ≤1%.
12 Position feedback current full stroke deviation calibration: input 4mA current (0%), then gradually increase the input signal 8mA current (25%), 12mA current (50%), 16mA current (75%), 20mA current (100%), Considering the nonlinear error of linear displacement converted into angle change, the 0%, 50%, 100% point feedback current error should be ≤1%, and the 25%, 75% point feedback current error should be ≤2%.
13 Position feedback current forward and reverse stroke variation test: the same as the positive piston reverse stroke test method of the cylinder, the actual positive and negative position feedback current ┠stroke relationship, the difference between the positive and negative stroke values ​​of the cylinder piston under the same feedback current value The value should be ≤1%.
14 Make a good verification record, fill in the contents of the verification record form item by item, and the inspector must sign.
15 After the above tests are completed, the terminal block of the position transmitter should be inserted, the back cover should be tightened, and then the gas source inlet of the valve positioner should be blocked with a plastic plug.
This item can be determined according to the actual situation.
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