1 . Check the chamber for cleanliness and proper lubrication. If necessary, remove all debris that may have been left in the chamber by a previous user. Wipe the cover O-ring clean and lubricate it with petroleum jelly. Wipe clean the inside lip of the chamber (where the O-ring seals). Install and remove the cover several times to insure smooth operation. See "MAINTENANCE OF INSTRUMENT" for additional cleaning instructions. It is better to clean and lubricate the instrument as described above at the end of each day than leave it to be cleaned the next time it is used.
2. Remove the chamber cover and turn the control valve to the OFF position.
3. Connect the supply hose to the pressure tank and to the instrument. Be certain that the quick-disconnect collar is pulled all the way back into its original position after the male hose end has been inserted. Check that both hose connections are secure by gently tugging on the hose. (See "Filling the Portable Tank" for a better understanding of this step)
4. Slowly open the valve on the pressure tank just enough to permit gas flow, usually about one-half turn. It is not necessary or desirable to open this valve completely. Do not attempt to disconnect the hose at the quick-disconnect fitting until all pressure has been released from the hose.
5. Test the safety valve. Instruments with a lug-type cover have a safety valve (located at the back on the right side of the chamber body). This valve vents the chamber if the cover is not completely closed. This valve MUST be tested at the beginning of each measurement session. Insert a solid rubber gasket into the cover and install the cover on the chamber body. Turn the cover clockwise to the stop and then back it off about 15 degrees to a position such that the cam on the cover does not depress the piston in the safety valve. The rate control valve should be nearly closed, but the exact position is not important as it will be adjusted later. Now pressurize the chamber by turning the control valve to the CHAMBER position. The safety valve should pop open before the pressure reaches 2 bar. If it does not, turn the control to EXHAUST, then remove the nut and piston of the safety valve and lubricate the O-ring on the piston with petroleum jelly. Reassemble and test the safety valve again. When the safety valve opens, the pressure in the chamber should drop to near zero. Turn the control valve to the EXHAUST position, completely close (rotate clockwise) the cover to depress the safety valve piston, and then back the cover (counterclockwise) 15 degrees to allow the valve to be tested again. Repressurize the instrument by turning the control valve to CHAMBER. This time the safety valve should open at a pressure below 2 bar. If it does not, remove the nut and piston of the safety valve and clean and lubricate the O-ring on the piston with petroleum jelly. Check for any foreign debris then reassemble and test the safety valve again.
The safety valve is an important safety component of the
instrument.
Do not attempt to operate the instrument until the safety valve is
operating
properly; that is, until it is releasing the chamber pressure at less
than
2 bar pressure,
As an added safety precaution, the cover should be left in only one
of two positions: 1 ) on the chamber and completely locked in place, or
2) completely removed from the chamber. The cover should never be
left in all intermediate positions. This section on safety valves
does not apply to chambers with a threaded cover (i.e. Model
650) as there is no danger of the vessel being pressurized with the
cover only partially installed.
6. Set the rate valve. With the solid gasket still in place, rotate the cover clockwise to the stop. Turn the control valve to the CHAMBER position. The pressure in the chamber should slowly increase. Adjust the rate valve until the pressure increases at the desired rate. For plants at low moisture stress use a rate of about 1 bar every 5 seconds. For plants with stress levels above 15 bar the rate of pressure increase should be about 1 bar every 2 seconds. Intermediate moisture stress levels require intermediate rates of increase in pressure. Finding the best rate of pressure increase for particular species and stress levels may require experimentation. Errors in measurement caused by a rate of pressure increase that is too high or too low tend to cause stress levels to appear higher than they actually are. Therefore any adjustments to the above guidelines should be such that the lowest measurements of PMS are achieved.
7. Turn the control valve to EXHAUST and remove the chamber cover. The instrument is now ready to use.
IMPORTANT - The above instructions are for the basic use of the instrument. Your instrument may have special characteristics such as the Model 610 (self-contained unit) is slightly different in filling the internal tank. Additionally, the Model 603 or 1003 (digital models) have additional electronic functions that need to be understood before using the instrument. You may read these additional differences here or consult additional specific directions included with these instruments for proper use.
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