Brooks Instrument 5850E - Manual (Page 30)

Brooks ® Model 5850E
3-10
Installation and Operation Manual
X-TMF-5850E-MFC-eng
Part Number: 541B102AAG
September, 2009
Section 3 Operation
3-5 Response
Fast Response Adjustment
Two methods of adjusting the step response of the Model 5850E mass
flow controllers can be used. No. 1 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. No. 2 describes
a method that will allow adjustment of the Model 5850E mass flow
controller to optimum 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 (5.000V) 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 zero percent flow indicates the adjustment required of the
anticipate potentiometer. Refer to Figure 3-7.
1. If the flow signal decays to -.05 to -.5 Volt, then rises to zero
Volts, the anticipate potentiometer is properly adjusted.
2. If the flow signal decays rapidly and goes below -.5 Volt before
rising to zero Volt, 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 -.5 Volt,
the anticipate potentiometer must be adjusted counterclockwise
and Steps “a” and “b” repeated.
Fast response adjustment (3 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 three
seconds (six seconds for Current I/O Version) after command 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 5850E and