MKS 246C - Remote Flow Control; How to Control Gas Flow with TTL Logic

Remote Flow Control Cha
p
ter Four: O
p
eration
66
Remote Flow Control
Remote control of the flow through MFCs is accomplished using TTL logic control. Interface
connector J9 provides the means to remotely turn the flow on and off, and to adjust and monitor
the flow rate in any channel using a set point signal from a voltage applied to J9. Refer to Table
7, page 33, for the Interface connector J9 pinout.
If an external voltage source is to be used for Ratio or External set point control, it can be applied
via either the "SP IN" microjack connector, or through pins 7 (+) and 3 (-) on Interface connector
J9.
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 J9. Refer to Table 7, page 33, for the Interface connector J9 pinout.
When the FLOW CONTROL SWITCH (refer to Figure 7, page 39) is placed in the REMOTE
position, a logic signal coming in through the Interface connector J9 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 53, to prepare the 246 unit and
the MFCs for flow control.
2. Place the SET POINT SOURCE SWITCH on all 246 units in use to the EXT position.
3. Place the FLOW CONTROL SWITCH on all 246 units in use to the REMOTE position.
4. Apply the control signals through Interface connector J9.
For example:
a. To produce a flow of 50 sccm through a 100 sccm MFC, apply a +2.5 V signal to
pin 7 on connector J9.
Reference this voltage to pin 8 (digital ground) on connector J9.
b. Attach a TTL signal to pin 4 on connector J9.
Reference this signal to pin 8 (digital ground) on connector P6.
c. Turn the flow ON by applying a TTL low (0.4 to 0.8 V) to pin 4 on connector J9.
d. Turn the flow OFF by applying a TTL high (2.4 to 5 V) to pin 4 on connector J9 or
an open circuit.