MKS 247D - Remote Flow Control with TTL Logic

Chapter Four: Operation Remote Flow Control
69
Remote Flow Control
Note
Ensure the MFCs and the 247 unit are
p
ro
p
erl
y
confi
g
ured as described in
How To Setup the System,
page 55.
Interface connector P6 provides the means to remotely turn the flow on/off and to adjust and
monitor the flow rate in any channel using a set point signal from a voltage applied to P6. Refer
to Table 7, page 32, for the pinout for Interface connector P6.
How To Control Gas Flow with TTL Logic
TTL logic control provides a way to use only a simple voltage level to control the flow rate. You
can create a custom interface by wiring the required control signals to the appropriate pins on
Connector P6. Refer to Table 7, page 32, for the Interface connector P6 pinout.
When the FLOW CONTROL SWITCH (refer to Figure 5, page 40) is placed in the REMOTE
position, a logic signal coming in through the Interface connector P6 may be used to gate the set
point signal to the MFC. A logic low turns the flow on; a logic high turns the flow off.
To use TTL logic control:
1. Follow the instructions in
How To Setup the System,
page 55, to prepare the 247 and the
MFCs for flow control.
2. Place the SET POINT SOURCE switches on all channels with a MFC attached to the
EXT position.
3. Place the FLOW CONTROL SWITCHES on all channels with a MFC attached to the
REM position.
4. Apply the control signals through Interface connector P6.
For example:
a. To produce a flow of 50 sccm through a 100 sccm MFC connected to Channel 1,
apply a +2.5 V signal to pin 4 on connector P6. Reference this voltage to pin 1 on
connector P6.
b. Attach a TTL signal to pin 12 on connector P6. Reference this signal to pin 8 on
connector P6.
c. Turn on the flow by applying a TTL low (0.4 to 0.8 V) to pin 12 on connector P6.
d. Turn off the flow by applying a TTL high (2.4 to 5 V) to pin 12 on connector P6 or
an open circuit.