MKS 651C, Instruction Manual, Page: 72 / 172

How To Set Lead and Gain Parameters Chapter Five: Local Operation
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How To Set Lead and Gain Parameters
When the 651 unit is configured for PID control, separate lead and gain parameters are
maintained for each pressure set point. Set point A is associated with Lead A and Gain A. Set
point B is associated with Lead B and Gain B, and so forth.
When an analog set point is used with PID control, the lead and gain parameters associated with
any of the pressure set points (set points A through E) may be used. To specify which set point’s
lead and gain parameters to use, apply a TTL low level signal to the I/O connector pin assigned
to the desired set point. Refer to Table 10, page 34, for a description of the pin assignments for
the digital inputs. The TTL low level signal (0 to 0.8 Volts) is “level sensitive” meaning that
once the signal is held low, the 651 unit may take up to 50 milliseconds to recognize the
command. The line must be held low continuously for the 651 unit to use the selected
parameters. Once the signal goes high, the instrument will default back to set point A parameters
within 50 milliseconds. For example, to apply the lead and gain parameters associated with set
point C to the analog set point, apply a 0 to 0.8 Volt signal to pin 14 (on the I/O connector) for as
long as you wish to use those parameters.
1. Hold down both arrow keys, [ ] and [ ] for approximately three seconds to enter
the Setup menu.
2. Scroll to the Control mode screen appears and verify that PID is selected.
3. If Self-Tuning is selected, turn the Adjust knob clockwise to select PID control.
4. Adjust the set point lead and gain parameters.
By careful adjustment of the lead and gain parameters, it is possible to achieve optimum
control throughout a wide range of pressure regions. Examples of Lead and Gain for set
point A are shown below.
LEAD A 1.25 SEC.
PRES 350 Torr
GAIN A 25.0%
PRES 350 Torr
5. Use the Adjust knob to enter the desired lead and gain parameters.
The 651 unit will use the lead and gain values associated with set point A by default.
If a set point is configured as a valve position, then no lead or gain parameters are associated
with it.