Instruction Manual
IM-106-880, Rev 1.0 January 2007
OCX 8800
5.An operator can calibrate and diagnostically troubleshoot the OCX 8800 in one of two ways:
a.LOI. The LOI is mounted to the end of the electronics module and allows local communications with the electronics. Refer to Section 4, Using the LOI, for more information.
b.Optional HART Interface. Each of the OCX 8800's 4-20 mA output lines transmit an analog signal proportional to oxygen or combustible levels detected. The HART output is superimposed on the oxygen
4-20 mA output line only. This information can be accessed through the following:
•Model 275/375 Handheld Communicator - The handheld communicator requires Device Description (DD) software specific to the OCX 8800. The DD software will be supplied with many Model 275/375 units, but can also be programmed into existing units at most Emerson Process Management service offices. Refer to Section 5, Using HART Communications, for additional information.
•Personal Computer (PC) - The use of a personal computer requires AMS software available from Emerson Process Management.
•Selected Distributed Control Systems - The use of distributed control systems requires input/output (I/O) hardware and AMS software which permit HART communications.
6.Optional Blowback System. The blowback system periodically blows instrument air back through the sample line filter and out the sample tube. This clears out particulate and keeps the sample line filter from clogging.
System Operation
Figure 1-2 shows the relationship between the components of the OCX 8800. The sensors and the electronics are contained in separate housings. The sensor housing and probe mounts to a duct or process wall so that the probe protrudes into the flue gas stream. An air powered eductor continuously pulls samples of the process flue gas through the probe to a chamber in front of the sensor housing where the sample passes the O2 sensor and continues on to the COe sensor. Dilution air is provided to the COe sensor and reference air to the O2 sensor. After the gas sample flows past the O2 sensor and through the COe sensor, it is drawn through the eductor where it mixes with the eductor air and exits through exhaust back into the system. The electronics housing contains the CPU and HART boards which convert the sensor inputs into 4-20 mA analog output signals. The CPU can also initiate and perform calibrations. Three test gasses and instrument air can be turned on and off by solenoids. Test gas flow to the sensors is regulated by a flow meter between the electronics and sensor housings. Instrument air is separated into eductor air, reference air, and dilution air. The instrument air solenoid does not allow air flow until the heaters are up to temperature. This minimizes the amount of sampled process flue gas being pulled into cold sensors causing condensation.
