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A Y290 on the western edge of Europe

By Patrick McArdle (Galway) August 2020

In August 1981 a small ad in Chemistry in Britain placed by Professor George Ferguson advertised a Hilger and Watts Y290 for £5,000. I contacted George in Guelph about buying it and he stressed that a Weissenberg camera was needed to get data collection started on the Y290. I knew of a long forgotten Weissenberg camera that was lying in a cupboard in another University in Dublin. I got permission to use the Weissenberg and I was sure that it could be added to one of the spare X-ray windows on our JEOL PXRD. I went to Professor Frank Coll, the head of the Chemistry Department in Galway, and said to him that we had recently spent more than £5,000 each on IR spectrometers and that I thought I could set up single crystal diffraction in Galway for £5,000. He told me that the University accountant would give me a cheque for £5,000 and he wished me good luck.

With my long-time friend and colleague Des Cunningham I went to Guelph and we stayed for a week with George Ferguson learning how to operate the Y290. We gave George the cheque and he told us that John Ralph had serviced the Y290 in Guelph and that we should get him to come to Galway when we had the machine setup.

We had absolutely no funds and setting up the Y290 in Galway could not have been done without the help of many people especially Professor Philip Walton from the physics department who had experience with X-ray generators, Kevin Carey of Digital Equipment in Galway and John Ralph. The existing X-ray setup in Galway had one generator connected to JEOL PXRD and XRF machines. Philip said he knew where there was a high voltage switch and 20 meters of HV cable which was out of use in one of the hospitals. To illustrate the type of practical help provided I have indicated in the diagram the setup we had and the HV switch labelled S.

I said to Philip “we don’t have any connectors for the ends of the HV cable at the X-ray tube or the switch”. He said “I will get one for the tube made up in the workshop” and then he picked up the cable at the point marked x cut it with his penknife stripped the cut ends pushed the wires into the HV sockets on the switch and filled the sockets with oil. The other great asset we had in Galway was the only Digital Equipment factory outside the U.S. I realized that we had a serious problem with the teletype in that it would not work with 50 Hz ac. I contacted Kevin Carey and asked him if he knew anyone who had a teletype and he told me that the Colaiste Iognaid secondary school in Galway known locally as the “Jes”, had been given a PDP11 and a room full of VT52 terminals by Digital and that they had teletypes for an older system which was now redundant. There can’t have been many schools that had that level of computer facilities in the early 1980s. A few years later Digital gave all Galway second level schools login facilities to a large computer in Galway

When we got the Y290 working any faults the PDP8 developed were repaired by Kevin Carey who would come during lunch hour and quickly find the flip chip where the fault was. John Ralph had told us that we were lucky not to have a straight 8 which had discrete transistors rather than the 7400 series logic DILs which we had. I believe that Hilger & Watts built 25 Y290s and then ceased production. John Ralph bought the rights and built 2 further machines one of which he sold to Max Perutz at MRC Cambridge and the other to the Pasteur Institute in Paris. The Y290 was operated using a teletype which was used to read in the programs from paper tape and punch the output onto paper tape. A full data set required a tea chest full of paper tape. We soaked the paper tape roll before use with Mazola cooking oil to lubricate the punch. We could not afford X-ray diffraction film for the Weissenberg so we used out of date hospital X-ray film. The paper tape was a lot of trouble and it was just possible to read the tapes into the University DEC20 computer. We collected data on about 50 crystals this way but to speed things up we needed to automate the Y290 operations and stop using Weissenberg unit cell data. John Ralph told us that there was an upgrade available based on a PDP11 which cost £45,000. We could not afford this so I learned some machine code programing using an Acorn Atom microcomputer and a PDP12 manual. I asked the University accounts department for a loan of £400 pounds to buy a BBC micro and then set about upgrading the Y290.

Retired Weissenberg camera, Y290, CAD4 and MAR in 2020

Automating the Y290

I wrote what I now know to be a disassembler program for the PDP8 on the Acorn Atom and analysed the PDP8 programs.

The plan devised depended on making a tiny alteration to the BIN LOADER program.

The PDP8 RIM loader program was loaded with the data switches and RIM loader was used to load BIN LOADER. BIN LOADER could then read in the programs needed to operate the Y290 from paper tape BIN LOADER had a go address of 7777. All of the Y290 programs had a go address of 0200.

The last instruction in BIN LOADER was HALT. By great good fortune there was a location on the same page as the HALT instruction which had 0200 in it. I changed HALT to JUMP INDIRECT/ the location containing 0200.

We left the data switches at 7777 and three reed switches were attached to the STOP, LOAD ADDRESS and START switches. The three reed switches were connected to three of the PIA pins on the BBC micro. Thus the BBC micro could by operating STOP LOAD ADDRESS and START run the BIN LOADER to get the PDP8 to read a program the BBC micro sent to it. The program would then auto start when it reached the JUMP INDIRECT (0200). Complete automation !!! and it worked. Seamus Kellehan a member of the chemistry department technical staff built several of these “interfaces” and we sold enough of them at a modest price to repay the University accounts department.

Getting rid of the need for unit cell and reflection data from the Weissenberg

The plan here was to use the Weissenberg to obtain a random orientation rotation photograph. This would be a curved version of the way other diffractometers used a flat Polaroid Camera to take random orientation photographs. In such a photograph each reflection can appear four times and the x and y values of these spots can be used to calculate Theta and Chi for each reflection. Setting these values on the Y290 allowed Phi to be obtained by spinning the Phi axis until the reflection was found. The second thing that was required was to incorporate the Busing and Levy 4-circle geometry calculations¹ , least squares on the cell dimensions and unit cell transformations into a FORTRAN program. Rex Dark of the mathematics department in Galway had a look at the Busing and Levy paper and said it should be OK. A few days later Rex returned with 7 pages of neat fountain pen equations and matrix transformations and asked if he could have a set of 12 reflections to try it out. I gave him a reflection set and started to write the FORTRAN version of Rex’s equations. I had not got very far with the programming when a few days later Rex returned to say that it worked and he handed me many pages of tiny writing. I asked him how he did it, did he use a calculator? “No” he said “I used 7 figure log tables”. This was an astonishing feat. The final version of this program was called BRVCEL² and I know that BRVCEL was in use in the Royal Military College in Shrivenham during the worst of the troubles in Northern Ireland.

The BBC micro driven Y290 increased the number structures to about 200. It was the first 4-circle diffractometer in Ireland north or south and was eventually replaced by a CAD4 which was the second 4-circle diffractometer in Ireland. The CAD4 was replaced by a MAR image plate, the first area detector system in Ireland, which had the Y290 tube shield and monochromator as its X-ray source. The Y290 and the CAD4 were used together for a while and we found that the ESDs on the cell dimensions were better on the Y290. This was a testament to the angle setting accuracy of the Y290 Moiré fringe method which was not affected by gear train wear or slack. The least squares part of BRVCEL was written by Tim Higgins and it showed up some errors in the first version of the unit cell least squares program that came with the CAD4. BRVCEL lives on in the Oscail software package which uses some of its subroutines to check and transform unit cells.³   

(1)  Busing, W. R.; Levy, H. A., Angle calculations for 3- and 4-circle X-ray and neutron diffractometers. Acta Crystallographica 1967, 22, (4), 457-464.

(2)  Higgins, T.; Dark, R.; McArdle, P.; Slmmie, J., BRVCEL—A computer program for cell reduction and Bravais lattice determination. Comput. Chem. 1990, 14, (1), 33-36.

(3)  McArdle, P., Oscail, a program package for small-molecule single-crystal crystallography with crystal morphology prediction and molecular modelling. J. Appl. Crystallogr. 2017, 50, (1), 320 - 326.

 

Patrick McArdle Lúnasa 2020