Agilent Technologies 7890A Manual

Agilent Technologies
Replacing the NPD Bead
Instruction Guide
NPD Bead Replacement.book Page 1 Monday, October 13, 2008 2:32 PM

2Instruction Guide
Notices
© Agilent Technologies, Inc. 2008
No part of this manual may be reproduced in
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tronic storage and retrieval or translation
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ment and written consent from Agilent
Technologies, Inc. as governed by United
States and international copyright laws.
Manual Part Number
G3430-90037
Edition
Third Edition, October 2008
Second Edition, September 2008
First Edition, March 2004
Printed in USA
Agilent Technologies, Inc.
2850 Centerville Road
Wilmington, DE 19808-1610 USA
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ment is provided “as is,” and is sub-
ject to being changed, without notice,
in future editions. Further, to the max-
imum extent permitted by applicable
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ticular purpose. Agilent shall not be
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Safety Notices
CAUTION
A CAUTION notice denotes a haz-
ard. It calls attention to an operat-
ing procedure, practice, or the like
that, if not correctly performed or
adhered to, could result in damage
to the product or loss of important
data. Do not proceed beyond a
CAUTION notice until the indicated
conditions are fully understood and
met.
WARNING
A WARNING notice denotes a
hazard. It calls attention to an
operating procedure, practice, or
the like that, if not correctly per-
formed or adhered to, could result
in personal injury or death. Do not
proceed beyond a WARNING
notice until the indicated condi-
tions are fully understood and
met.
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3
Replacing the NPD Bead
Instruction Guide
Agilent Technologies
Replacing the NPD Bead
7890A and 6890 Gas Chromatographs
This instruction guide reviews the procedure for installing a
bead on a nitrogen- phosphorus detector (NPD). Before
following this procedure, refer to the safety information on the
inside front cover and in your GC user information.
Parts list
•1 NPD bead assembly (ceramic or Blos)
•Cap for the bead
•Test chromatogram
NOTE If you used Blos beads before 2008, you may notice that the current bead
has a slightly different shape and color. This is normal.
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4Instruction Guide
Replacing the NPD Bead
Required tools
•T- 10 Torx screwdriver
GC Firmware
•If using a 7890A Series GC, it is recommended that the
firmware version is A.01.09 or higher.
•If using a Blos bead on a 7890A Series GC, make sure the
firmware version is A.01.09 or higher.
•If using a 6890 Series GC, make sure the firmware version is
A.03.05 or higher.
•If using a Blos bead on a 6890 Series GC, make sure the
firmware version is A.03.08 or higher. (Firmware versions
earlier than A.03.08 will immediately destroy a Blos bead if
you use the Adjust Offset feature.)
Figure 1 Blos bead assembly
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Replacing the NPD Bead
Instruction Guide 5
Preparing the GC
1 Gather the following:
•Lint- free gloves
•T- 10 Torx screwdriver
2Set the NPD bead voltage to 0.0. (Do not set it to Off.)
Agilent data system users: After setting the bead voltage to
0.0, save the data system method and shut down the
instrument session. (Note that in some data system versions,
you may need to use the GC keypad to set the voltage. To do
this, the GC keypad must be unlocked and you must close the
GC parameters screen of the data system. Upload the revised
setting, then save the method and shut down the instrument
session.)
3Set Adjust Offset to Off.
4Cool the detector to 60 °C or lower. Leave all gas flows on. To
cool the detector faster, raise the GC detector cover and open
the hinged NPD cover.
CAUTION The bead is delicate. Be careful not to break or crack the bead. When
performing maintenance on the NPD, avoid touching the bead with
your fingers, and prevent it from coming in contact with other surfaces.
WARNING Hazardous voltages are present when the electronics top cover is
open.
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6Instruction Guide
Replacing the NPD Bead
5Remove the necessary GC covers.
•7890A models: Raise the GC detector top cover. Loosen
the screw on the electronics top cover and lift cover
(Figure 2).
•6890 models: Gently lift the gray plastic detector top
cover (with the holes and ventilation slots).
For models with the hinge bracket: The hinge is a
metal bracket attached to the oven top. Pull the clip at its
top toward you to release the hinge pin. Push the pin to
the left to release the cover. Raise the cover and remove it.
Remove the top electronics cover. Push the clips
underneath the cover (shown in Figure 3) toward the
center to disengage them.
Figure 2 Lifting the electronics top cover (7890A)
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Replacing the NPD Bead
Instruction Guide 7
Other models: Push the clips underneath the cover toward
the center to disengage them.
Figure 3 Removing the top electronic cover (6890)
Clips
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8Instruction Guide
Replacing the NPD Bead
Removing and Installing the Bead
1Put on lint- free gloves before touching any of the detector
parts.
NOTE The illustrations below show a ceramic bead. Blos bead installation is the
same.
WARNING Be careful! The oven or detector fittings may be hot enough to cause
burns.
CAUTION Wear clean, lint-free gloves to prevent contamination of parts with dirt
and skin oils.
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Replacing the NPD Bead
Instruction Guide 9
2Twist the ring to disconnect the bead assembly cable. Push
and twist the lock so that the button slides up in the groove,
then pull the cable ends apart.
1
2
3
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10 Instruction Guide
Replacing the NPD Bead
3Remove the 3 T- 10 Torx screws from the bead assembly.
4Gently lift up and remove the old bead assembly. Avoid
bumping the bead on the sides of the collector.
5Remove the protective cap covering the new bead.
Bead assembly
NOTE For a new Blos bead, the bead should be centered as shown in Figure 1. If
you notice that the bead assembly does not appear like the assembly
shown in Figure 1, carefully center the bead. Be sure to not contaminate
the bead during this process.
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Replacing the NPD Bead
Instruction Guide 11
6Mount the new bead assembly on the NPD lid. Be careful not
to bump the bead on the sides of the lid or collector.
7Replace the screws. Finger- tighten the first screw; tighten
the remaining screws normally and then completely tighten
the first screw. Do not overtighten the screws.
8Carefully bend the bead assembly cable 90 °.
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12 Instruction Guide
Replacing the NPD Bead
9Reconnect the bead assembly cable to the NPD cable and
twist the ring to lock the connection.
10 Close the NPD cover and reinstall all GC covers. All covers
must be closed to get a stable NPD baseline.
11 For the 7890A GC, configure the new bead.
•Set the bead type.
•Review the Maximum Bead Voltage setting and adjust, if
necessary.
•Review the Dry Bead and Auto Adjust Bead settings.
12 Restore normal NPD operating gas flows.
13 With all gases on, heat the detector to 150 °C and hold for
about 15 minutes, then increase the temperature to 250 °C
and hold for 15 minutes.
14 Increase the temperature to operating value (310 to 320 °C
recommended). Allow 15 minutes for equilibration.
1
2
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Replacing the NPD Bead
Instruction Guide 13
15 Check the NPD leakage current.
aDisplay the detector output.
bVerify that the output (leakage current) is stable and
< 2.0 pA.
If > 2.0 pA, verify bead installation and recheck. If still
high, replace the ceramic insulators; inspect/replace the
collector.
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14 Instruction Guide
Replacing the NPD Bead
Turning On the Bead
Now that the bead is installed, it is turned off but warm, with
gases sweeping any evaporating moisture off of the bead and
out of the detector. Next you will adjust the bead voltage to
achieve the desired response using either the Adjust Offset
process (recommended for the 7890A GC with firmware A.01.09
or greater) or manually.
Set the Initial Bead Voltage to a Safe Value
Before you turn on the bead for the first time, manually set its
voltage to a safe value so that the new bead is not destroyed.
1Make sure Adjust Offset is turned Off.
2After the temperature stabilizes at setpoint, set the initial
Bead Voltage, depending on bead type:
•Blos bead: 0.0 V to 0.5 V
•Ceramic bead (white or black): 0.0 V to 2.0 V
To Use the Adjust Offset Process to Set Bead Voltage
If you choose to use the GC Adjust Offset process, do the
following:
1Set the offset.
•Blos bead: 20 pA
•Ceramic bead (white or black): 30 pA
2If your GC has an Equilibration time, set it to 0.0.
3If using an Agilent data system, start the online session for
the instrument.
For 7890A users: If you changed the bead type, you will need
to resolve the current method to match the new bead type.
4When the GC becomes Ready, start Adjust Offset.
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Replacing the NPD Bead
Instruction Guide 15
To Manually Adjust the Bead Voltage
After the bead reaches the initial voltage, begin to increase the
voltage value in 0.05 V increments until the bead ignites. Wait
about 10 seconds between each voltage adjustment. Monitor the
detector output. When the bead ignites, the output will rise
suddenly, then decrease towards a more stable value. It is best
to allow the NPD to remain in this state without further
adjustment for about 24 hours. Then you may adjust the bead
voltage in small increments (0.05 to 0.1 V) until reaching the
desired offset. With a clean environment, clean gas supplies,
and low bleed column, a typical offset may decrease 6- 12 pA
during a 24 hour period.
Blos Beads
•A new Blos bead typically ignites between 0.5 and 1.1 V.
•A Blos bead typically requires a lower offset than the white
and black beads to achieve a similar response.
•A new Blos bead shows an increase in baseline during a
temperature programmed analysis. This effect minimizes
after a few cycles.
Recommended flow settings (starting values):
Capillary makeup flow: 1 to 20 mL/min
If using He makeup gas,
recommend < 10 mL/min to
avoid cooling effects.
Hydrogen flow: 1 to 3 mL/min
Air flow: 120 mL/min
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16 Instruction Guide
Replacing the NPD Bead
Ceramic Beads (White or Black)
•A new ceramic bead typically ignites between 2.8 to 3.2 V.
Recommended flow settings (starting values):
Capillary makeup flow: N25 to 10 mL/min
He < 5 mL/min
Hydrogen flow: 2 to 5 mL/min
Air flow: 60 mL/min
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Replacing the NPD Bead
Instruction Guide 17
NPD Cleanliness
Below is an overview of typical NPD leakage currents for a
system set to recommended flows and temperature.
When changing insulators and seals, cool the detector to 75 °C
or below. This will minimize the chance of stripping the three
T- 20 Torx screws.
The installation of traps is recommended for the detector,
hydrogen, air, and make- up gas. A moisture trap followed by
chemical traps is highly recommended.
pA Leakage Current System status Comment
0.3-0.9 CLEAN
1.0+ Dirty Decrease in sample response.
10+ Very dirty Almost no sample response.
Cause is usually contaminated ceramic
insulators on the collector - usually the
upper insulator and seal.
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Agilent Technologies
© Agilent Technologies, Inc.
Printed in USA, October 2008
G3430-90037
NPD Bead Replacement.book Page 18 Monday, October 13, 2008 2:32 PM