Brooks Instrument SLA7840 - Manual (Page 23)

3-5
Model SLA7840
Section 3 Operation Installation and Operation Manual
X-PR-SLA7800-RT-eng
Part Number: 541B048AAG
August, 2009
D. Valve Override
This input allows the valve to be forced to its most closed state or its most
open state, regardless of setpoint. If this input is not electrically connected
the MFC will operate according to the current values of the other MFC
inputs. If this input is held at 0 Vdc, the valve will be forced to its most
closed state. If this input is held to +15 Vdc the valve will be forced to its
most open state.
E. Mode Select Pin
Pin 13 on the 15 pin 'D' connector allows for selection of RT operating
mode. The Mode Select Pin is controlled similar to operating a switch. If
the connection to the pin is 'OPEN', then the RT will operate in its flow
control mode. If the connection to the pin is 'CLOSED' to Signal Common
(Pin #10), then the RT will operate in its pressure control mode.
When the mode select pin changes state, the device performs any
required processing to change the mode, then returns to normal operation.
Typical time required to change modes is approximately 0.5 seconds.
NOTE: It is recommended to change operating modes during no-flow
conditions.
F. Zeroing the RT (Self-zero)
It may be desirable to re-zero the flow sensor if it is operated at its
temperature extremes or if it is positioned in an attitude other than that
specified on the customer order.
Note: Before zeroing the instrument, zero pressure differential MUST be
established across the device. If there is pressure across the device during
the zero process, any detected flow through the sensor will be
misinterpreted as the zero flow reading. This will result in calibration
inaccuracy during normal operation.
Once zero differential pressure is established and verified, press the
recessed, momentary push-button (Self-zero button) located on the side of
the device (see Fig. 3-2) to start the Self-zero function.
The zero process requires approximately 200 msec. During this time, the
device will set its output signal to 0.0 Vdc.
3-5 DeviceNet Mode of Operation
For information on DeviceNet capabilities for Brooks Model SLA7840 refer
to the DeviceNet Supplemental Instruction Manual (X-DPT-DeviceNet-
SLA7000-RT-eng).