MKS 937B - Page 50

MKS 937B Operation Manual
50
Nominal Range is the flow range specified on the MFC based on its factory
calibration gas. To set the Nominal Range, move the cursor to the Nominal Range
box, press
Enter
, and use the and keys to select the full scale flow rate for the
MFC. Note that the MFCs always employ unit of SCCM in 937B and the valid range
is 0.1 to 1.00E+6 sccm (1000 SLM).
3. Zero
When YES is selected for the Zero function, the output of the controller will be set to
zero. The default for this function is NO.
Since the MFC and the 937B both control the gas flow, to be correctly zeroed a gas
flow must have both the MFC and the 937B be set to zero. The recommended
procedure for zeroing a MFC is:
 Step 1: Zero the 937B display
Since the MFC does not have a local display, the 937B MFC display
must be zeroed before performing the zero of a MFC. The procedure for
setting the display to zero is
a) Disconnect the MFC cable from the back of the MFC board inside of
the 937B controller;
b) Short the MFC signal input pins (pin 2 and pin 12) of the 15pin HD
Dsub connector on the back of MFC board;
c) Set Zero to Yes. When Yes is selected, “Ensure pin 2 &12 are shorted,
pressure Enter to execute” will be displayed since the 937B can detect
if a MFC is connected to the board.
d) Press Enter to execute the display zero process. Once the Enter
button is pressed, the Offset DAC will be set to the factory default, and
the ADC will be zeroed;
e) If multiple MFCs are connected to the 937B controller, individual
channel displays must be zeroed separately.
 Step 2: Zero the MFC
After the 937B display has been properly zeroed, it is STRONGLY
recommended that the MFC be zeroed as follows:
a) Ensure that the gas flow inside of the MFC is zero. This can be done
by equalizing the pressure across the MFC;
b) Adjust the zero pot on the MFC so that the indication on the 937B
display is zero.
c) Once this has been done, the MFC zero process is complete (step 3 is
not required).
Note: occasionally, an MFC is installed in such a manner that it is not
accessible (e.g. inside a gas cabinet). When this occurs, skip this step and
go directly to step 3.
 Step 3: Zero the 937B controller
If Step 2 is executed, this step is not required.
a) Ensure the gas flow inside the MFC is zero. This can be done by
equalizing the pressure across the MFC;