Brooks Instrument 5861i - Manual (Page 22)

3-6
Installation and Operation Manual
X-TMF-5861i-MFM-eng
Part Number: 541B111AAG
November, 2008
Brooks ® Model 5861 i
Section 3 Operation
3. Adjust the linearity potentiometer for an output equal to the new TP2
voltage and then repeat step k.
Note: The voltage at TP2 can range from -3 to +3 volts, however, it is
recommended that this voltage stay between -2.5 and +2.5 volts for proper
operation. If the recommended voltage range is exceeded the desired
accuracy and/or signal stability may not be achieved. If one of the limits is
reached, check the restrictor sizing. Refer to section 4-6.
3-5 Response (Flow Output Signal)
To achieve the proper response characteristics the response
compensation circuit must be adjusted. This adjustment is performed by
observing the output signal of the meter when the flow is suddenly
stopped. Place a metering valve upstream of the Model 5861
i to control
the flow rate. A Brooks NRS TM precision metering valve is well suited for
this application. Also place a fast acting shut-off valve immediately
downstream of the flowmeter. A solenoid valve is ideal for this, but a
manual toggle valve will do. Keep the length of interconnecting tubing as
short as possible between the valves and the Model 5861
i since the tubing
can have a dampening effect on the flow and the gas may not stop flowing
the instant the downstream valve is closed. Adjustment of the fast
response circuit will not alter the steady state accuracy of the flowmeter as
adjusted in Section 3-4.
Note: This procedure requires an oscilloscope chart recorder, or a DVM
with a sampling speed of three samples per second or greater to monitor
the rate of change of the output signal during the test. Monitor the output
signal at pin 2 of D-Connector. TP4 may be used for circuit common.
a. With the shut-off valve open adjust the metering valve so that the
output voltage of the Model 5861 i is 4.050 to 5.000 Vdc. Allow the
output to stablize at this setting.
b. Close the shut off valve to stop the flow. Observe the output signal as
it decays.
c. The behavior of the output signal during the transition between 100%
and 0% flow indicates the adjustment required of the anticipate
potentiometer. Refer to Figure 3-4.
1. If the flow signal decays to -0.05 to -0.5V then rises to 0.0V, the
anticipate potentiometer is properly adjusted.
2. If the flow signal decays rapidly and goes below -0.5V before rising to
0.0V, 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 -0.05V, the
anticipate potentiometer must be adjusted counterclockwise and
steps a and b repeated.