Sentry Sample Sentry II High Pressure, Installation, Operation & Maintenance Manual

Page: 9 / 45

Sentry Sample Sentry II 9
Upon power being supplied to the Sample Sentry II, the unit enters its startup routine.
During Startup, always ensure that unit’s sample isolation valve is closed (located next
to customer connection 1 in Figure 1 and Figure 2). During this startup routine, the unit’s
revision date and a Sentry logo are displayed. See Figure 3. During the unit’s startup
routine, the fully open and fully closed position of the PRV is being located. After the PRV
positions are stored, the system returns the PRV to the home setting and enters Operation
screen in Manual mode. Refer to Figure 5. Any time that the Sample Sentry II power is
reset, the unit enters its startup routine.
Sample Sentry II has two modes of operation, Manual and Automatic. Automatic mode is
comprised of the following states: Start , Blowdown , Sample , and Stop .
Start is the first state in Automatic mode. While in the Start state the valves V-1 and SV-2
are closed. The PRV should be in its home set point position. For older models, this home
set point is not customer adjustable and is set to zero. On new models, the PRV home
set point position can be customer adjustable between 0 and 100 percent (0 being fully
closed and 100 being fully open). The system continually monitors the inlet pressure at
PT-1 and compares it to a programmed Startup Pressure set point in the controller. When
the inlet pressure is greater than the Startup Pressure set point, the system advances to
the Blowdown state. If Blowdown is not enabled, the system goes to the Sample state.
When enabled, the Blowdown state initiates a controlled blowdown sequence by opening
V-1 and closing SV-2. Blowdown is designed to flush the sample line while preventing
flow to analyzers. The controller continually adjusts the PRV, maintaining a flow rate at
the programmed blowdown flow rate set point. By closing SV-2, sample flow to analyzers
is stopped and the entire sample flows to the grab sample. Sample Sentry II remains
in the Blowdown state until the blowdown timer expires. The blowdown timer is a
programmable set point in the controller.
Â
NOTE
Ensure sufficient blowdown time and flow rate are obtained to remove debris from the sample
stream prior to sending sample to the analyzers .
After blowdown, Sample Sentry II advances to the Sample state. In the Sample state, SV-2
opens allowing flow to analyzers. The controller continually adjusts the PRV, maintaining
a flow rate at the programmed sample flow rate. The system remains in the Sample state
until one of the following conditions is met:
1. Low Flow
a. The PRV is full open.
b. The total flow rate falls below the shutdown flow rate set point.
2. Low Pressure
a. The pressure falls below the shutdown pressure set point.
When one of the above conditions is met, the system advances to the Stop state. In the
Stop state, the controller closes SV2, adjusts the PRV to its home set point, and then closes
V-1. After all three valves are in their respective positions, the system advances to the Start
state if automatic startup is enabled or Manual mode if disabled.