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Chapter 6. CRAMPS/Multipulse Module Tests
48
UNITY
INOVA Solids Hardware Installation 01-999044-00 C0501
h. Enter
go
. Check rf power of about 44 dBm.
i. Stop the acquisition. Set
tpwr=50
and set HI BAND to HI POWER.
Confirm rf power of about 50 dBm at the preamplifier.
j. Set
tpwr=63
. Restart and check for 900 W (59.5 dBm) or more at the
preamplifier.
If the “overdrive” interlock comes on, check the interlock adjustment.
Otherwise, stop the acquisition.
k. Reconnect the transmitter cable to the preamplifier. Connect the spectrum
analyzer to the PROBE port on the preamplifier. Repeat step g above, making
sure that loss through the preamplifier is less than
1.0 dB.
7. Observe the pulse shape using a 8 ms pulse width. Do not confuse the rf pulse rise
and fall times with the amplifier turn-on and turn-off times. The pulse droop for an
8 ms rf pulse would be 3% or less.
8. Confirm the absence of any amplifier gating/blanking transient pulses coincident
with the external amplifier gating signal.
Testing the Gating
1. Stop the acquisition. Select LO POWER on both HI BAND and LO BAND. The
scope should still be connected to the probe port.
2. Set the following parameters:
rof1=0.2 pw=2e3
3. Enter
go
. Trigger on blanking signal J7024 and observe rf. Determine the gating
delay by measuring the time at which the rf is fully on. Add 200 ns to this value. The
liquids amplifier should gate on in less than 2
µ
s.
4. Repeat steps 1 through 3 with both HI BAND and LO BAND set to HI POWER. The
rf should gate on in less than 2
µ
s.
Checking Decoupler Transmitter Performance
Confirm that the decoupler transmitter output to the probe is normal (as for liquids) when
the LO BAND switch is set to LO POWER. The decoupler should perform as in a liquids-
only NMR spectrometer and should be under the control of
dpwr
as usual.
Some parameters in the acquisition group may not be displayed by the
dg
command if they
are set to zero. Be aware of power parameters like
tpwr
,
dpwr
,
dlp
,
tpwrf
,
dpwrf
, and
pulse lengths. Check their values at experiment setup!
Testing the Amplifier
Typical power outputs are given as a guide to troubleshooting. Pulse droop should be
recorded on all systems, but accurate power measurements are only needed if the system
fails to make pulse width or
γ
B
2
specifications. A spectrum analyzer should be used for
accurate power measurements.
To Test the AMT Decoupler Amplifier (Channel A)
The maximum drive to the AMT amplifier should not 2 dBm. This should be
checked for the decoupler as follows:
1. Disconnect the input to Channel A of the AMT amplifier with fixed attenuators in-
line and connect it to a power meter.