Cambridge Sensotec Rapidox 1100ZR-H-PFC-E O
2
Analyser Instruction Manual
Version 1.2
45
Last printed 22/07/2015 18:08:00
point control begins again until the reading is established back inside the
window. And so on.
27)
O
2
Regulation Low Point:
As described above this value sets the lower
limit of the target O
2
window. Note that the low point can be set to the
same value as the high point to give maximum control around a set point,
but this is likely to cause the gas valve to “chatter”. It is normal practice to
have a window of several ppm to get best operation from the valve.
Note that the target oxygen value is always the mid-point of the window defined
in 2 & 3 above. So for example if your target oxygen value is 100ppm you may set
the upper value to 110ppm and the lower value to 90ppm. Once running the PFC
will open and close the gas valve to bring the oxygen reading down to inside the
window 90-110ppm. Once inside the window the valve is not moved any further
until the value drifts out of the window. At this point the PFC will start
controlling again to bring the reading back inside the window. The net effect is a
stable reading very close to the desired set point with minimal valve control.
28)
Max Flow Control Value (%):
This parameter allows the user to restrict the
maximum amount you can open the gas valve by in terms of a percentage
(0-100%). This is useful for damping the system if required. A value of
100% means that the valve can be allowed to open fully if so required by
the PFC.
29)
Min Flow Control Value (%):
This is the opposite parameter to 4) allowing
the user to set a minimum amount that the gas valve can be opened in
terms of a percentage 0-100%. A value of 0% means the valve can fully
close if so required by the PFC. Note that for obvious reasons the minimum
value must be smaller than the maximum value set in 4).
30)
Positive Regulation Gain:
This is the “P” term in PID (Proportional
Integral Differential) control. This P setting affects how the PFC behaves
when the oxygen reading is above the window setting defined in 2) and 3).
The value is entered as a positive number between 0 and 100,000 (normally
less than 10). The P term looks at the current oxygen reading and compares
it to where the desired oxygen value is. The difference in the two values is
multiplied by the P value and the resulting value is used to open and close
the gas valve. In more simple terms it is a “speed of response” factor where
a bigger value makes a big change and vice versa.
31)
Negative Regulation Gain:
This P setting affects how the PFC behaves
when the oxygen reading is below the window setting defined in 2) and 3).
The value is entered as a number between 0 and 100,000 (normally less
than 10) and works in exactly the same way as described in 6) above. In
most applications they are given the same value.
32)
Integral Regulation Gain:
This is the “I” term in PID control. The I term
is a correction factor that looks at any offset caused by the P term working
on its own and makes a correction to improve the final target oxygen value.