Brooks Instrument 4800 Series - Manual (Page 20)

3-2
Brooks ® 4800 Series
Section 3 Operation Installation and Operation Manual
X-TMF-4800-MFC-eng
Part Number: 541B072AAG
September, 2013
temperature difference measured by the two temperature sensors to
increase with increasing flow. The temperature difference is then converted
into a flow signal based on the factory calibration.
There is one major difference between a traditional thermal mass flow
sensor and the MEMS based sensor. A traditional thermal mass flow
sensor makes use of a Cp transfer function. However, as depicted in
Figure 3-1, only a portion of the flow field is heated by the MEMS sensor.
Therefore, a Cp transfer function cannot be used in the MEMS sensor to
adjust the flow rate for a gas other than what the device was calibrated on
when it left the factory.
3-3 Features
Note: All Brooks Series mass flow meters are configured at the
factory according to customer order and do not require adjustment.
Not all features are available on all instruments.
The Brooks 4800 Series device is a full-featured digital MFC. The device
performs much like a traditional analog MFC, but with improved step
response and valve control. The analog interface matches that of Brooks'
popular analog MFCs so it can be retrofitted into tools using analog MFCs.
3-4 Analog I/O Mode of Operation
The following paragraphs describe the basic features of the Brooks 4800
Series instruments.
Functional Description
The analog interface may include any of the following I/O options as
specified by the user:
0 - 5 Vdc setpoint, 0 - 5 Vdc flow output
4 - 20 mA setpoint, 4 - 20 mA flow output
Also included is the Valve Override input pin. All analog signals available
are on the 15 pin D-Connector. (See Fig. 1-1 for connections.)
Before operating the MFC/MFM, apply power and warm-up the instrument
for approximately 15 minutes. After warm-up, apply gas pressure then
proceed by following the instructions in the following sections.
Setpoint Signal Input (MFC Only)
This input allows the user to establish the MFC setpoint. Several input
types are available as follows: