Brooks Instrument 5851E - Manual (Page 30)

3-10
Brooks ® Model 5851E
Section 3 Operation Installation and Operation Manual
X-TMF-5851E-MFC-eng
Part Number: 541B104AAG
November, 2008
flow controller is not critical to overall system performance. No. 2 describes
a method that will allow adjustment of your Model 5851E 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 (3 seconds response specification not
guaranteed)
Note: This procedure requires an oscilloscope, chart recorder or a DVM
with a sample speed of three samples per second or greater to monitor
the rate of change of the output signal.
a. Set the command potentiometer for 100% of flow (5.00 V) and wait
about 45 seconds for the flow output signal to stabilize.
b. Step the command signal 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 3-7.
1. If the flow signal 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 (3 second response specification guaran-
teed)
Adjustment of the anticipate potentiometer to obtain a flow rate perfor-
mance to be within 2% of flow rate commanded in less than 3 seconds
after set-point change requires the use of a fast response flowmeter
(500 millisecond response to be within 0.2% of final value or better) in
series with the Model 5851E and a storage oscilloscope or recorder.
a. Make a step in command to the controller from 0 to 100% of full
scale flow and record the output signal of the fast response flowme-
ter.
b. If this signal shows more than 4% overshoot, adjust the anticipate
potentiometer 1/2 to 1 turn counterclockwise. If the signal does not
show overshoot, but is not within 2% full scale of final value after 3
seconds, adjust the anticipate potentiometer 1/2 to 1 turn clockwise.
Set command potentiometer for 0% of flow.
c. Repeat Steps a and b until the fast response flowmeter output signal
meets the specified response requirements.
Note: With the above equipment, the anticipate potentiometer can
be adjusted to give optimum response characteristics for any
process.