Varian UNITY INOVA NMR, Hardware Installation, Page: 47 / 65

Chapter 6. CRAMPS/Multipulse Module Tests
46
UNITY
INOVA Solids Hardware Installation 01-999044-00 C0501
To find the amplifier input/output match, begin with the TUNE at one extreme and
then adjust the LOAD for a maximum. Then move the TUNE 20% towards the other
extreme and readjust the LOAD for a new maximum. Continue in this way (40%,
60%, . . .) noting each apparent maximum. The greatest maximum is in the region of
the match. Continue to refine the adjustment in this region to achieve maximum
output power.
4. Make fine adjustments to the input tuning and matching for maximum output.
5. If a gain of 14 dB is not achieved, it may be necessary to repeat step 3 and 4 with the
output coupling in a new orientation.
6. Adjust the protection circuit current set point to approximately 20% above the grid
current level measured with a scope at 1 kW output.
7. Reassemble the amplifier.
Tuning the Cavity Amplifier During Normal Operation
Routine tuning is done during the initial installation in the field and on a regular basis
during normal operation. The routine tuning procedure involves neither access to high
voltages nor disassembly of the amplifier.
1. Apply 46 dBm of power in 1 ms pulses with 10% duty cycle to the amplifier by
setting the following parameters:
seqfil='s2pul' pw=1e3 tn='H1'
sw=1e5 at=.01 d1=0 nt=1e6
2. Attempt to maximize the output power while minimizing the grid current. Adjust
both TUNE and LOAD to maximize the output. The gain should be 14 dB at 46 dBm
input.
To find the amplifier input/output match, begin with the TUNE at one extreme and
then adjust the LOAD for a maximum. Then move the TUNE 20% towards the other
extreme and readjust the LOAD for a new maximum. Continue in this way (40%,
60%, . . .) noting each apparent maximum. The greatest maximum is in the region of
the match. Continue to refine the adjustment in this region to achieve maximum
output power.
3. Make fine adjustments to the input tuning and matching for maximum output.
Adjusting the Overdrive Interlock
WARNING:
Dangerous high voltages over 2200 Vdc exist inside the high voltage
section. Contact with a bare terminal can result in serious injury or
death. The high-voltage section has tuning adjustments. Only qualified
service personnel shall remove the cover.
1. Power down the 1 kW high-band amplifier EHT.
2. Remove the 1 kW high-band amplifier from the cabinet.
3. Remove the top cover from the low-voltage side (wider cover).
4. Locate on the control board (see schematic 87-195723-00) the test point TP2, which
is on the lower right side of the board (zone P5).
5. Connect a Fluke DVM (or equivalent) to the test point on 20 Vdc range.
6. Determine the current interlock level by measuring the voltage from the test point to
the ground. Using A = V/62, verify that for 120 mA level, V = 7.44.