Model 520 HT UCA
D01157216
Revision A, October 2015
28
software. Make certain the system is holding pressure before proceeding.
The pump contains metal-to-metal inlet and outlet check valves that may
not be bubble tight, so a small amount of pressure leakage is to be expected.
This should not be a problem under normal operation.
5.
Turn the blue PRESSURE REGULATOR knob counterclockwise slowly
until the test cylinder pressure begins to drop. Continue turning the
regulator knob slowly until the pressure in the test cell is at the upper limit
of the desired test pressure.
6.
Release pressure in the test cell using the PRESSURE RELEASE valve.
7.
Turn the AIR TO PUMP regulator counterclockwise until the AIR TO
PUMP is approximately zero.
8.
Turn the PUMP switch ON in the software.
9.
Slowly turn the PUMP AIR PRESSURE ADJUST regulator knob
clockwise until the pump actuates. Continue to slowly turn the regulator
knob clockwise until the lower limit for the control pressure is reached.
As the test cylinder gets hot, pressure in the test cylinder will increase. When the
pressure in the test cylinder exceeds the control pressure upper set point, the
pressure regulator will open and pressure will be reduced. If the heating rate is
reduced, as during the transition from a temperature ramp to a temperature soak,
the pressure in the test cylinder may decrease. If the pressure falls below the
control pressure lower limit, the pump will actuate and bring the pressure back
within the established limits.
The pump and pressure regulator will have hysteresis or a “deadband” in their
operation. For example, if the pressure regulator is set to open at 3000 psig, it may
open at 3000 psig, but may not close until the pressure falls to some lower value,
perhaps 2900 psig. This 100 psig differential between opening and closing is
referred to as the deadband or hysteresis. As another example, the pump may be
set to actuate if the pressure falls to 3000 psig, but the pressure may reach perhaps
3100 psig before the pump stops. This 100 psig differential between the initial
pressure and the final pressure is also known as deadband or hysteresis. If the
upper and lower set points are too close together, this deadband may overlap and
cause system instability. The system will then go into a continuous oscillation
where the pump increases pressure and the pressure regulator releases all the
pressure the pump is able to build. The solution to this problem is to decrease the
lower set point, raise the upper set point, or both.
7.2
Stopping a Test
When the test has been completed, follow the steps below to end the test.
