Brooks Instrument Mfi Series - Manual (Page 36)

3-8
Brooks ® Mf Series
Section 3 Operation
Installation and Operation Manual
X-TMF-Mfi-Mfx-MFC-eng
Part Number: 541B074AAG
August, 2009
3-5 Response
Fast Response Adjustment (Controller)
Two methods of adjusting the step response of the Mf Series mass flow
controllers can be used. Number 1 below, describes a method that will get
the step response close to optimum quickly and without any flow
measuring equipment. This method should be used when the response
time of the flow controller is not critical to overall system performance.
Method Number 2 describes a procedure that will allow adjustment of your
Mfx Series mass flow controller to optimum step response performance.
This method is the preferred way to adjust the step response. Adjustment
of the fast response circuit will not affect the accuracy of the flow controller
as adjusted in Section 3-4.
1. Fast response adjustment (six seconds response specification not
guaranteed)
Note: This procedure requires an oscilloscope, chart recorder or a DVM
with a sample speed of three sample per second or greater to monitor
the rate of change of the output signal.
a. Adjust the setpoint for 100% flow and wait about 45 seconds for the
flow output signal to stabilize.
b. Step the setpoint to 0% or activate valve override closed to stop the
flow. Observe the flow signal output as it decays.
c. The behavior of the flow signal during this transition between 100% and
0% flow indicates the adjustment required of the anticipate
potentiometer. Refer to Figure 3-6.
1. If the flow signal measured on TB-1, Terminal 5, decays to -.05 to -.5 V,
then rises to 0 V, the anticipate potentiometer is properly adjusted.
2. If the flow signal decays rapidly and goes below -.5 V before rising to
0 V, the anticipate potentiometer must be adjusted clockwise and
Steps a and b repeated.
3. If the flow signal decays slowly and does not go below -.05 V, the
anticipate potentiometer must be adjusted counterclockwise and
Steps a and b repeated.
2. Fast response adjustment (six second response specification
guaranteed)
Adjustment of the anticipate potentiometer to obtain a flow rate
performance to be within 2% of flow rate commanded in less than six
Figure 3-6 Fast Response Adjustment