Brooks Instrument SLA5800 Series - Manual (Page 37)

3-5
Brooks ® Digital MFC's & MFM's
Section 3 Operation Installation and Operation Manual
X-TMF-SLA5800-MFC-eng
Part Number: 541B027AAG
April, 2013
Valve Override (MFC Only)
Connector Pin 12 on the 15 pin D-Connector 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 or -15
Vdc the valve will be forced to its most closed state. If this input is held at
+5 Vdc or greater (max. = 24 Vdc), the valve will be forced to its open
state.
Calibration Select Pin
Connector Pin 13, on the15 pin D-Connector allows selection of one of ten
calibrations stored in the device. This pin is designed to accept pull-down
resistors referenced to common (Pin 9).
Table 3-1 shows typical resistor values required for selecting calibrations 1
through 10. Note, these resistor values should be within ± 1% tolerance.
The default condition is with no resistor connected which activates
Calibration #1.
When the calibration select pin changes state, the device performs any
required processing to change the calibration, then returns to normal
operation. If the device determines that the selected calibration is not valid,
(where applicable) the valve is driven to the closed state and the flow
signal is set to zero. Typical time required to change calibrations is
approximately 1.0 second.
NOTE: It is recommended to change calibration curve selection during no-flow
conditions.
Zeroing the MFC (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 instrument 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 Figure 3-2) to start the self-zero function. The zeroing process requires
approximately 10 mseconds.
CAL# RESISTOR VALUE (K ohms)
1 Open
2 Shorted
3 665
4 324
5 191
6 124
7 80.6
8 52.3
9 30.9
10 15
Table 3-1 Typical Resistor Values for Calibration Selection