Re: R.F. pulse monitor
Jim Breeyear (jbreeyea@moose.uvm.edu)
Mon, 01 Apr 1996 08:39:39 -0800
Cindy Ridenour wrote:
>
> Paul Driscoll wrote
>
> >... do you trust the pulse programming software to produce
> >what you code? For example I am trying to program the gradient enhanced
> >HNCACB experiment - many pulses and gradients on three channels including
> >1H and CO decoupling during the 'evolution'/'mixing' portions of the code.
> >I am not getting any signal (well, I get only noise). So how you I start to
> >debug all this? ...
>
> At this point in the discussion, I feel it is necessary to add my two cents
> worth on the subject of pulse program debugging. This is not really the
> topic of this conversation, but I am concerned that some folks may be
> misled by some comments that are being made. (And I don't mean to pick on
> Paul, his is just the latest message.)
>
> While I do have bird lines in place to monitor forward and reflected power
> at the probe, I do not use this set-up for debugging pulse sequences. Many
> liquids power amplifiers and probes are capable of handling CW at full
> power without causing meltdowns in the equipment. However, that is because
> those instruments are power limited. Not all instruments are power
> limited! This is especially true for solids-equipped instruments, or older
> equipment without hardware and software safety features.
>
> Unless you are certain that your instrument is incapable of delivering
> damaging power levels under CW conditions, you should _never_ test a new
> pulse sequence at high power (i.e., at the probe).
>
> Find a place on your instrument to break into the line after phase,
> freqency, and amplitude are set, but prior to high power amplification.
> (On a CMX instrument, this is the "RF out" BNC connector on the front of
> each transmitter.) Feed this output into an oscilloscope or other device.
> You have now broken the circuit to the high power amplifier. Now you can
> test a just-written pulse sequence safely. If you do accidentally code an
> infinite loop or make some other mistake, you will not have to worry about
> your hardware and software protection for your probes and amplifiers,
> because they are no longer in line.
>
> As one who learned from experience, testing at high power can be an
> expensive and time-consuming mistake. When I made the mistake, I was a
> graduate student. I and my colleagues had to rebuild everthing from the
> amplifier to the probe to the preamp. So, be safe.
>
> Happy Pulsing!
>
> Cindy Ridenour
>
> Applications Scientist
> Otsuka Electronics USA Inc
> 2607 Midpoint Drive
> Fort Collins, CO 80525
> (970) 484-0428 FAX: -0487
> cindy@otsuka.comI agree with you Cindy. I am more inclined to pick a place in the console
where the voltage and power levels are low. We have a BLT-5 which we can
break into from the front. We dont however run complicated pulse programs
so maybe it is better to monitor at the probe for that. Yes! Duty cycle
is everything when it comes to damage. I burned up a preamp because a
decimal point was in the wrong place on one variable. I also thought I
would be clever and build my own 19F decoupler and when I hit "zg" it
fried the coil. We did get results but unfortunately too many. Jim.