YOKOGAWA ZO21DW, User Manual, Page: 31 / 39

<7. INSPECTION AND MAINTENANCE>
7-2
IM 11M03A02-00E
7.1 Inspection and Maintenance of the Detector
7.1.1 Cleaning the Calibration Gas Tube
The calibration gas, supplied through the calibration gas inlet of the terminal box into the detector,
flows through the tube and comes out at the tip of the probe. The tube might become clogged
with dust from the measurement gas. If you become aware of clogging, such as when a higher
pressure is required to achieve a specified flow rate (600±60 ml/min), clean the calibration gas
tube.
To clean the tube, follow these steps:
(1) Remove the detector from the installation assembly.
(2) Following Section 7.1.2, later in this manual, remove the four bolts (and associated spring
washers) that tighten the sensor assembly, and the pipe support as well as the U-shaped
pipe.
(3) Use a rod 2 to 2.5 mm in diameter to clean the calibration gas tube inside the probe. In
doing this, keep air flowing from the calibration gas inlet at about 600 ml/min and insert the
rod into the tube (3-mm inside diameter). However, be careful not to insert the rod deeper
than 40 cm for a general-purpose detector, or 15 cm for a high-temperature detector.
(4) Clean the U-shaped pipe. The pipe can be rinsed with water. However, it should be dried out
thoroughly before reassembly.
(5) Restore all components you removed for cleaning. Follow Section 7.1.2 to restore all
components in their original positions. Be sure to replace the O-ring(s) with new ones.
F7.1E.ai
Calibration gas tube
Exploded view of components
Rod
(with outside diameter
of ø2 to ø5 mm)
Figure 7.1 Cleaning the Calibration Gas Tube