MKS 1253D, Инструкция по эксплуатации

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Chapter Four: Operation How To Tune the 153/1253 Controller
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How To Tune the 153/1253 Controller
1. Apply power to the 153/1253 unit and turn on the upstream gas source(s).
2. Apply the desired analog set point signal or an RS-232 message.
The 153/1253 unit responds by changing the pressure smoothly to the desired value. If
the pressure is slow changing to the desired value (over 30 seconds), or oscillates, then
adjust the LEAD and/or GAIN. Use the RS-232 communication link to change the
LEAD and GAIN values. Refer to RS-232 Communications, page 46, for a description
of the control characters to use.
3. Increase the LEAD setting if the pressure overshoots the selected value.
If there is no overshoot, and particularly if the pressure is slow approaching the set point
value, then reduce the LEAD setting. Repeat this test to confirm that the LEAD setting
is appropriate. Note that the correct LEAD setting for a rise in pressure is normally not
the same LEAD setting for a drop in pressure. Therefore, duplicate the test for the
LEAD parameter with the same set point and direction as required in the process.
4. Reduce the GAIN setting if the pressure oscillates about the correct value.
The highest possible GAIN setting produces the best pressure control, therefore, reduce
the GAIN setting in very small increments.
Note
The speed of pressure response is relative and depends on chamber size
and absolute pressure. Lower pressures (less than 10 microns) are usually
slower because of the slower molecular flow and reduced pumping speed.
The maximum rate of rise of pressure is determined by the following formula (with the exhaust
valve fully closed).
Pr = F/V
Where: Pr = pressure rate of rise in Torr/sec.
F = flow in Torr-liters/sec.
V = volume in liters.
Consequently, in systems with small input flows and relatively large volumes, the pressure will
rise slowly even when the control valve is fully closed.
If the controller cannot achieve good control, the problem may be caused by improper pneumatic
connections. Refer to System Considerations, page 26, to read about factors which effect
pressure control.