MKS 247D - Set Point Signal; Set Point Signal Source

Set Point Signal Cha
p
ter Three: Overview
36
Set Point Signal
The set point signal that is sent to each MFC through connectors J1 to J4 may be generated in a
variety of ways:
•
Manually
using independent gas flows or by ratioing the gas flows for one to
three channels to the flow in Channel 1
•
Externally
using a set point signal from an external controller, or by ratioing
gas flows based on the set point signal from an external controller and
measurements from a pressure transducer
•
Remotely
using TTL logic control
Set Point Signal Source
The flow rate is determined by the magnitude of the set point signal with +5 V corresponding to
full scale flow. The set point signal can be generated by:
•
An internal +5 V reference
•
A ratio signal from Channel 1 or an external controller
•
An externally applied voltage
The source of the set point signal is selected by the three position SET POINT SOURCE
SWITCH on the front panel (refer to Figure 5, page 40), as either FLOW, RATIO, or EXT. The
FLOW and RATIO positions of this switch are driven by the output of the SET POINT
CONTROL; the EXT position is driven by an externally applied voltage.
The output of the SET POINT CONTROL is driven by an internal dipswitch (S15), located on
the rear of the Main PC board. The 247 unit is initially configured so that the ratio set point
signal is based on the Transducer Output of Channel 1 (the internal reference). To change the
configuration so that the source of the set point signal is based on the External Ratio Amplifier,
you must change the dipswitch settings in S15. Refer to
How To Change the Dipswitch Settings
,
page 64
,
for more information.