MKS 250E - How to Use Manual Control; How to Tune-Up the Controller

How To Use Manual Control Cha
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ter Four: O
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eration
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How To Use Manual Control
The 250 controller has a MANUAL control which, when properly adjusted, should make the
initial valve turn-on quick and easy.
Place the valve selector in MANUAL and increase the MANUAL control setting. During the
first few turns nothing will happen to the flow (or pressure in the system). The numbers on the
MANUAL control are meaningless except to allow the operator to return to a known position.
When the signal to the valve is large enough to exceed the valve offset, the valve begins opening.
At this point you can fine-tune the MANUAL control to set a flow into the system to produce the
desired pressure. Leave the MANUAL control in the set position in order to produce the
quickest and smoothest transition from CLOSE to AUTOMATIC.
How To Tune-Up the Controller
Turning the valve mode switch (CMAE) to AUTO puts the controller into action. If the SET
POINT control is set for the same pressure (or flow) that the MANUAL control had established,
then the transition from MANUAL to AUTO should be smooth and bumpless.
To tune the controller, turn the GAIN up until 0.1% oscillations are apparent. Minimize
oscillation amplitude using PHASE LEAD settings. When oscillations cease, turn up the GAIN
and readjust the PHASE LEAD if necessary. Check the settings by changing the SET POINT
control. Optimum response is for the error to reduce to zero quickly, but with no overshoot. If
the pressure oscillates (error meter swings from positive to negative) the GAIN is too high. The
GAIN may be increased later when the PHASE LEAD is properly adjusted. If the pressure
overshoots, but settles to the proper value, more PHASE LEAD is required. If the pressure is
slow rising to the proper value, less PHASE LEAD is required. If the pressure settles at a steady
value, which is other than the set point (greater than ±0.25% error), more GAIN is needed.
When making final adjustments, move the controls less than 10° to prevent overcontrolling.
Various pressures will require different settings of GAIN and PHASE LEAD although pressures
up to a decade apart may be controlled using the same settings. Speed will be sacrificed for
lower pressures.
Note
On controllers with the DVM option, the system error will have to be
calculated by subtracting the set point value from the displayed value.