5.4.5.8  NMR Operationg Procedure:

In principle it is possible to make the field measurements using the SEARCH mode in the Teslameter. In this mode you select a probe and the meter explores the whole field range of the probe until it finds and "locks" on the resonant signal indicating that it has a field measurement. A "lock" is indicated on the controls display by positive field values. This has the advantage of simplicity but in practice can be time consuming and doesn't always work. The problem being, in situations where there is a lot of noise mixed in with the signal, the circuitry has problems distinguishing the signal from the noise and gets lost before it ever finds a lock. The problem is exacerbated when the field being measured is at the high end of the probe's range. In this case the search starts at the low end and keeps getting hung up on the noise and never gets to the field range of interest. The solution to this problem is to tell the device approximately what field it's looking for and use the AUTO mode to find the lock. In the procedure below that is what we will be doing.

In any case, for "gap probes" (group 0) you must energize and adjust the gradient compensating coils for the field ranges to be measured before trying to make measurement.

For studies involving 10% changes in the field settings the compensating coil current can be set once and left alone.

Recommended Procedure:
For group 0 probes set compensating coils appropriately (see figures above).
Put meter in MANUAL mode with SEARCH OFF
Select a probe and polarity. (Group 0: Probes 0, 1, 2 negative; underlineProbes 3, 4, 5 positive)
Type in DAC number for the field range being measured (see below)
Select AUTO and wait for a lock (positive field reading)
Verify that you have a good lock by checking the oscilloscope for a clear resonant signal.
Go back to 2. for the next probe
If you have problems see the table listing problems and possible solutions.

Selecting DAC #'s

In selecting the DAC # to use for the field of interest use either the graph in figure  or the polynomial below that.

Problems and Solutions

Symptom	Diagnosis and Cure
Weird numbers on displays, controls for	(Call James Proffitt)
all magnets fouled up	Need to reboot.
NMR Teslameter does not respond to	Meter's communications are
	somehow hung up. Turn
commands and display shows all zeros.	power off and on to the meter.
	At present this requires that you
	go down into the hall.
Will not lock	Very high noise level
	makes resonance hard to find.
Still will not lock	Very high noise level makes
	resonance hard to find. Search
	for the resonance manually by
	adjusting the DAC in manual
	mode until you see the resonant
	signal. (It helps if you know
	what field you expect so you'll
	know where to look)
You find resonance manually	Check probe polarity.
but still can't get a lock	Try decreasing and
	increasing DAC number by 1.
	Optimize signal by adjusting
	compensating coils
Can't find resonance manually	Try a different probe. Use
	readings from other probes to
	tell you where to look for
	the resonance with the probe
	that's giving you trouble.
	Make sure compensating coils are
	energized properly.
	Make sure magnet is on

• Hadron Dipole Field Setting Instructions: