VICI D-2-I - Manual (Page 29)

25
Electron Capture Mode (PD-D2 only)
Since the PDHID mode provides a better indication of the cleanliness and
the integrity (leak-tightness) of the system, we utilize that mode for initial
testing. If the system is operating according to the parameters described
thus far, it is ready for operation in the PDHID mode. To configure the
PD-D2 to operate in the PDECD mode:
1. If the discharge is not already established, turn on the MAINS switch and
the DISCHARGE switch. The discharge should start within five minutes.
2. Set the MODE switch on the controller to PDECD.
3. Set the detector temperature with the TEMPERATURE control knob.
4. Set the electrometer RANGE switch to 1X. (The high detector back-
ground current associated with the PDECD mode normally precludes
operation in the 10X range).
5. Leave the BIAS-B cable alone. Remove the BIAS-A cable and move
the ELECTROMETER cable to the bottom electrode. Remember that
connections should be finger-tight only.
High voltage will be present on the BIAS-A cable
during operation. Cover the end of the cable with
tape or otherwise protect the end from accidental
contact with persons or equipment.
6. Disconnect the column and leave the column inlet open. Reinstall the
column as indicated in on page 17. The suggested range for the column
position is from 99 to 102 mm, wherein the detector response (not the
background current) is within 90% of the maximum. Since there may be
some variation in the flow rate for the different types of capillary columns,
you may need to optimize the column position within this suggested
range.
7. With the dopant line still disconnected, set the dopant gas (3% xenon in
helium) flow rate to 5 - 7 mL/min (±0.2 mL/min). (In some circumstances,
methane in helium may be used as the dopant to affect a cost savings.
Consult the factory for recommendations.)
8. Remove the plug from the DOPANT port on the detector and replace it
with the dopant gas line.
9. Check the BIAS-B voltage, indicated by the controller DISPLAY. If the
displayed voltage is 0.5 - 1 V at room temperature, the system is ready
for operation. (A bias voltage less than 0.5 V can result in an unstable,
erratic, and noisy system.)
In the PDECD mode, the bias voltage is internally controlled to obtain a
constant detector current, set by means of the CURRENT switch. The
power-up default value for this current is 10 nA at 1X (1 nA at 10X), which
does not normally need to be changed. A higher set current results in a
more sensitive detector, but with a correspondingly reduced linear range.
Mode Selection and Setup