I've been trying to get a CPMG T2 pulse sequence to run on an AC-300
(with process controller) using the external address advance feature.
You've probably figured by now that it's not going well...
OK, first things first... tried out the Bruker supplied EXTAD.AUR to see
whether or not this breed of spectrometer could even do that sort of
thing. It works fine, and gives results which are essentially identical
to "normal" aquisition using GO. The EXTAD.AUR looks like...
;EXTAD.AUR
; DATA AQUISITION UNDER EXTERNAL ADDRESS ADVANCE
1 ZE
2 D1 ;RELAXATION DELAY
3 P1 PH1 ;90 DEG. TRANS. PULSE, RECEIVER BLANKING
4 D5 ;2*D5+D7=DE, HOLD PHASE AND BLANKING
5 D7 ADC ;D7 = 2 usec; INITIALIZE ADC
6 D5 PH2 ;SET DETECTOR PHASE, OPEN RECEIVER GATE
7 P8:X ;EXT DWELL PULSE, P8=1usec, DIGITIZE DATA AND INCREMENT
;ADDRESS
8 D8 ;D8=DW-1usec, DWELL TIME = P8 + D8
9 L1 TO 7 TIMES C ;LOOP TO 7 FOR `C' DATA POINTS IN FID
10 RCYC=2 PH3 ;LOOP FOR NEXT SCAN, OPTIONAL PHASE PROG.
11 EXIT
PH1=0 0 2 2 ;TRANSM. PHASE (OR USE :A)
PH2=0 0 0 0 3 3 3 3 ;DETECTOR PHASE (NORMALLY 0)
PH3=R0 R0 R2 R2 R1 R1 R3 R3 ;RECEIVER PHASE (OR USE QP)
;P1 IS EQUIVALENT TO PW
;D5 IS EQUIVALENT TO DE/2
;D7=2usec
;P8=1usec
;D8=DW-P8
;VC LIST CONTAINS VALUE OF TD
The above works well. A question arises though...What is the difference, if
any, between a "DETECTOR PHASE" and a "RECEIVER PHASE"?
In order to do a CPMG T2 (or try to) using external address advance
(it _should_ be possible if the above works) I wrote:
1 ZE
2 D1 ;RELAXATION DELAY
3 P1 PH1 ;90 DEGREE PULSE
4 D5 ;D5 = DE/2
5 D7 ADC ;INITIALIZE ADC, D7=2 usec
6 D6 PH4 ;BEING STINGY WITH TIME, SO D6=(DE/2)-2 usec
7 P8:X ;TAKE THE FIRST DATA POINT (THE "ZERO" TIME POINT IN CPMG)
8 D2 ;DEPHASING DELAY
9 P2 PH2 ;180 DEGREE REFOCUSSING PULSE, 90 DEG PHASE SHIFTED
10 D2 ;WE ONLY WANT EVERY OTHER ECHO TO CANCEL 180 DEG PULSE
11 D2 ;ERRORS, SO 2 X D2
12 P2 PH3 ;REFOCUSSING 180 DEG PULSE, PHASE SHIFTED 270 DEGREES
13 D2 ;AT END OF D2 ECHO IS REFOCUSSED
14 L1 TO 7 TIMES C ;LOOP TO 7, TAKE A DATA POINT AND CONTINUE WITH
;`C' DATA POINTS
15 RCYC=2 PH5 ;RCYC TO 2 FOR NS SCANS THROUGH THE LOOP
16 EXIT
PH1=0 2 1 3
PH2=1
PH3=3
PH4=0 0 0 0 3 3 3 3
PH5=R0 R2 R1 R3
When I run this, only get the first data point... it doesn't seem to like
all the other pulses in between the P8:X statements. If the P8:X is truly
independant of the dwell clock, then it should trigger each time through
the loop. If I put the 'scope on the spectrometer, all I get is the
initial 90 degree pulse. It does all of the correct delays, but I can't
see the alternating phase 180 degree pulse train (typically 300 pulses
separated by 100 usec). If I do the "normal" Bruker supplied CPMG, the
pulse trains show up as expected.
The ADC gets turned on when it sees line #6 D6 PH4. Now, according to
the manual (which I know is shaky at the best of times) one may put any
pulse sequence they want in between the ADC and RCYC commands. I have
tried blanking the 180 degree pulses using P2:E's but no luck has been
had. As far as I can figure, if the ADC is on, then no pulses are allowed
through the transmitter (which is, I imagine, a protection feature for
the detector?)
As an alternative, I tried the following:
1 ZE
2 D1 ;RELAXATION DELAY
3 P1 PH1 ;90 DEGREE PULSE
4 D5 ;D5=DE/2
5 D7 ADC ;INITIALIZE ADC
6 D5 PH2 ;SET THE PHASE AND OPEN UP THE RECEIVER
7 P8:X ;TAKE A DATA POINT
8 EOSC ;AS AN ALTERNATIVE TO RCYC, EOSC ALLOWS THE PS TO
;CONTINUE WITHOUT INCREMENTING THE SCAN COUNTER
9 D2 ;DEPHASING DELAY
10 P2 PH3 ;180 DEG. PULSE, 90 PHASE SHIFTED FROM INITIAL 90
11 D2 ;WE'RE TAKING ONLY EVEN ECHOES HERE, TO CANCEL IMPERFECT
12 D2 ;180 DEG PULSES
13 P2 PH4 ;FINAL REFOCUSSING PULSE, 270 DEG PHASE SHIFTED
14 D3 ;D3=D2-(2*D5+D7), REFOCUSSING DELAY SHORTER THAN D2 TO
;ALLOW FOR TIME REQUIRED TO SET UP ADC ETC.
15 L1 TO 4 TIMES C ;LOOP FOR C ECHOES, C DATA POINTS
16 GO=2 PH5 ;TAKE NS SCANS
17 EXIT
When this is run, the 180 degree pulse train looks lovely on the scope,
but (and this is a big one) the trigger on P8:X doesn't happen. The other
scary part is that the ADC light on the console stays lit through the
pulse train. Introducing a receiver blanked pulse (P2:E) for the 180's
doesn't allow the pulses to make it to the probe.
I've been going over this for a couple of days and can't get it figured
out... it should be (?) a trivial excercise (well, it is on an MSL).
If there's anyone out there that might have attempted this type of thing
on an AC before, I'd be interested in hearing of your exploits,
successful or otherwise.
I guess you might wonder WHY we want to do this on an AC... we managed to
justify our inflated budget a few years ago with the purchase of a high
temperature water cooled probe, allowing us ridiculously high and very
stable temperatures (up to 600 C). In the polymer game, T2's on glassy
or crosslinked polymers at >200 C is a nice thing to do routinely without
voiding our probe warranty.
Thanks all,
Tim Bremner
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Z Y' : DR. TIM BREMNER, Inst. for Polymer Research |
| / : :: Department of Chemistry, U. of Waterloo |
|/ : : : :: Waterloo, Ontario, CANADA, N2L 3G1 |
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/| : : : : :: Ph: 519-885-1211 x2510 |
/ | : : :: Fax: 519-888-6179 |
/ | :: E-mail: tbremner@polymer.uwaterloo.ca |
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