Brooks Instrument 5850i - Manual (Page 21)

3-3
Brooks ® Model 5850i
Section 3 Operation
Installation and Operation Manual
X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December, 2008
3-3 Zero Adjustment
Each 5850i is factory adjusted to provide a zero ±10 mVdc signal or a 4
mAdc ±0.05 mAdc signal at zero flow. The adjustment is made in our
calibration laboratory which is temperature controlled to 21.1°C (70°F
±2°F). After initial installation and warm-up in the gas system, the zero flow
indication may be other than the factory setting. This is primarily caused by
changes in temperature between our calibration laboratory and the final
installation. The zero flow reading can also be affected, to a small degree,
by changes in line pressure and mounting attitude.
To check zero, always mount the controller in its final configuration and
allow a minimum of twenty minutes for the temperature of the controller
and its environment to stabilize. Using a suitable voltmeter or current
meter, check the controller output signal. If it differs from the factory
setting, adjust it by removing the lower pot hole plug which is located
closest to the controller body. Adjust the zero potentiometer (refer to Figure
3-6) until the desired output signal is obtained.
NOTE: If the 0-20 mA output is used, adjust zero by monitoring the voltage
output signal. This is required because the current output cannot go
negative.
Figure 3-2 Flow Control System Block Diagram