8270A/8370A
Operators Manual
36
Static Control Mode
Static Control sets the pressure slightly above or below the target pressure value
and then turns off active pressure control, see Figure 8. The pressure is allowed
to naturally change until it is outside the Control Limit band. This pressure control
sequence repeats until the target pressure is changed or the test is complete.
The advantage of this control mode is that pressure can be set and measured
without noise from the pressure control system. Static Control shows in the user
interface as Static. A
Ready
indication is predicated on pressure being inside the
Control Limit and the rate of change of pressure is less than the Stability Limit.
The default Control Limit is zero (0) and the default Stability Limit is 0.7 kPa/min
(0.1 psi/min).
Target Pressure
APPLIED PRESSURE
Time
Static Pressure Control
Control Limit
Control Limit
+
-
Target
pressure
set
Rate of
pressure
decreased
to prevent
overshoot
Pressure
control
stops
Pressure
gradually
decreases
Pressure
hits Control limit
and controlled
up to
target pressure
ier017.eps
Figure 8. Static Pressure Control Mode Example
As an example, if the target value is 1000 psi, and the Control Limit is manually
set to 0.5 psi and the Stability Limit is set to 0.1 psi/min, the Product gives a
Ready
condition if the pressure is between 999.5 psi and 1000.5 psi and the
rate of change of pressure is less than 0.1 psi/min.
Slew Rate (Rate of Pressure Change)
Slew Rate is a user-defined maximum pressure rate of change. The Product
controls this pressure with minimum overshoot into a wide variety of external
volumes at its highest slew rate. In most applications Fluke Calibration
recommends that the slew rate be set at its maximum rate value. This provides
the highest speed control without jeopardizing overshoot or control stability
properties. In applications where the DUT could be damaged by high rate of
pressure change, it can be necessary to slow down the slew rate (control speed).
The Product control algorithm limits the rate of pressure change to the slew rate.
On calibrators with full-scale pressures ranges <70 kPa (10 psi), it is common to
reduce the slew rate to <25 % of full scale/min to improve on control overshoot
characteristics.
