Pulsed field gradient recovery test

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Field gradient pulses in the probes (pfg - pulsed field gradient) are created by the temporary application of direct current (DC) to a coil resident in the probe.

After the current stops, there will be residual currents induced in the other conductive parts of the probe that are called "eddy currents". Those will interfere with the transmitter/receiver coil, so that - for example - it will be impossible to record an fid until those transient currents die out.

A simple NMR experiment sketched below allows to determine how long it takes the probe to recover after the application of PFG:

Pulse sequence image

NMR signal will appear highly distorded if drecovery is too short.

Varian systems

Consult your system manual for the limit on durations and strength of gradient pulses.

With triple axis gradient systems (Performa XYZ) an additional parameter gradaxis will be required

pfgon='yyy'  #make sure your pfg unit is turned on in software 'yyy' setting is for triax gradients
gradtype=... #corresponding to your probe, eg 'ttt'
create('gradaxis','string') #it may already exist in the environment
gradaxis='z' #or 'x' or 'y' depending on which one needs to be tested

With other systems:

p1=0             #there is one pulse in the sequence the is not used
tpwr=62          #transmitter power for the 90o pulse
pw=5.5           #width of 90o pulse
lb=10            #10 Hz line broadening for data processing

For setting gt1 and gzlvl1 parameters consult your probe installation manual

gt1=0     #zero is safe for your probe, but useless, 1 millisecond is typical
gzlvl1=0  #consult your probe installation manual, this will depend on which axis is tested

for y axis

gradaxis='z'     #with triple axis probe

for x and y axes


add long recovery (1 second) reference spectrum to the array


Run the experiment, then process data

wft ds(arraydim) vsadj   #adjust vertical scale for display using the last spectrum
dssh                     #display spectra stacked horizontally

All spectra maybe excluging the first on must have equal intensity.

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