Yokogawa Single Channel Oxygen Analyzer System ZR22/ZR402 - Manual (Page 17)

17
IM 11M12A01-01E-A
Two (2) band heaters are pre-attached and pre-wired to a heater controller, mounted in a NEMA 4X
enclosure at the ZR22P adapter. The temperature controller is factory set for a high alarm set point
of 700
°F. If this alarm set point is exceeded, the controller will shut off the power to the heaters.
A Type J thermocouple is included to maintain the temperature of the adapter at approximately
600
°F. The solenoid valves that control the overall blowback system are also prewired. Two separate
limit switches are used to control the eductor solenoid and the blowback solenoids. The limit
switches are mounted in a separate enclosure
Eductor Solenoid Normally Open (NO)
Block Valve Normally Open (NO)
Blowback Air Solenoid Normally Closed (NC)
The end user must provide contact closure to input #1, terminals 13 & 15 to the ZR402G in order to
initiate blowback.
7.3.2 Operation of the ZR22P Control
The ZR22P has a separate electrical control circuit mounted at the adapter tee for blowback control.
Standard operation of this unit requires connection to the ZR402G Oxygen Analyzer contact output
#3.When the ZR402G initiates a blowback sequence (after a contact closure to contact input #1),
the blocking valve will close, the eductor valve will close, and the blowback air valve will be pulsed
by the ZR402G contact output. The pressure switch is preset to 0.7 psi on fall, which will prevent
the opening of the block valve if there is any pressure trapped in the transport tube due to an
unsuccessful blowback. When the blowback air cycle is finished and all the pressure has returned to
less than 0.7 psi, the blocking valve will open and the eductor valve will open. See the sequence of
events in chart 7.1.
NOTE: When Relay 3 is activated, Heaters #1 and #2 are disabled. Relay#3 latches ON until 115V
power is cycled OFF.
7.3.3 Blowback Timing Sequence
Event 1: Blowback is initiated with the contact closure from the ZR402G. Closure is at least 1
second.
Event 2: Block Valve is closed.
Event 3: Air Eductor is closed by the block A limit switch. The Air eductor cannot close unless event
2 has occurred.
Event 4: Blowback solenoid is pulsed at 10 second intervals, as received from the ZR402G contact
output. Although the actual pulse from the ZR402G occurs 2 seconds after the contact
closure, the air flow for blowback is briefly delayed until Events 2 and 3 have occurred.
Event 5: Block valve opens after delay timer of 15 seconds lapses, and the pressure switch indicates
that the residual pressure blowback is normal (less than 0.7 psi).
Event 6: The air eductor is opened, so that air flows through the eductor. Sampling of the process
returns to normal.
The duration of the blowback pulse is determined by the Calibration Time programmed at the
ZR402G in menu C4. The block valve will remain closed because of the relay timer, which
is shipped with a preset time delay of 15 seconds. The timer is not adjustable. At the end of
the blowback time (as set in the C4 menu), and the time delay, the block valve will open and
the air eductor solenoid will open.
NOTE: Blowback should only be performed as needed, as extreme blowback frequency will cause a
long stabilization time for reading to return to normal levels after blowback.