They were working on the early crane safe-load indicators. The M7402 had been superseded by the M7701 series, which came in various forms, but the exact details have been blurred by time. My first encounter was with the M7701B, which used a Perspex ring, filled with mercury as a boom angle sensor and used resistors switched into the circuit as a measure of the angle of the crane's boom. My job was to wind and assemble oscillator transformers used to provide a square wave signal to drive the load cell bridge. This was a compression cell mounted in a frame, which produced a signal proportional to the hoist rope tension. Later models for telescopic cranes measured the hydraulic pressure in the lift rams of the crane, and a pendulum turning a wire-wound 'pot' measured the boom angle. The boom length was measured by a cable reeling drum and all the signals were computed to provide a load moment signal for comparison with tables of permissible safe load for the various crane configurations. In those years, Phil Stride and Bill Thompson led the development team with Roy Barrett and Derek Hutchins doing the donkeywork!
Development of the safe load indicators continued for over twenty years and the last type to be made at Southend was the Microguard 300. By then this part of the business had been bought by the Morgan Crucible Group and was subsequently sold to the US distributor, The Gerald Greer Company.
Going back to the Sixties, some months after working on the safe load indicators, I was introduced to a new project, AMDI – 'Acoustic Miss Distance Indicator'. While this was being developed in Eric Fielder's lab, across the corridor Tim Davis's medical physics team, led by Bob Hubbard, was working on equipment for the earliest days of nuclear medicine. In another corner, Phil Allen and Arthur Shawforth were working on the RMDI system – 'Radioactive Miss-distance Indicator'.
The RMDI was intended for use with sub-sonic missiles, Bloodhound, Sparrow, Sidewinder and finally Rapier. RMDI used a radioactive source tagged to one of the tail fins of the missile. Both AMDI and RMDI systems used towed targets flown on the end of a mile or so of piano-like wire, streamed from the back of a Meteor or Canberra aircraft. The RMDI target contained a scintillator and photo-multiplier to detect the radiation from the source on the missile as it passed. The measurement was tele-metered back to the aircraft on a UHF band where the mis-distance was classified into one of four calibrated zones.
AMDI by contrast was for supersonic shells and relied on the amplitude of the N-shaped pressure wave generated by the projectile. This was sensed by a precision Bruel & Kjaer microphone.
One of my interests at home at the time was making and playing hi-fi at ear punishing levels. Because of my interest in sound recording, I found myself working on the microphone for the AMDI. I found the whole process fascinating and worked for several months on the high impedance amplifier for the microphone. This was housed on the end of a thin tube poking provocatively from the front of the target. In those days hi-tech miniature electronics amounted to a couple of new fangled silicon transistors on a half inch wide lump of fibreglass PCB. I spent a long time trying to fit this quart into its quarter pint pot!
As the shell passed the target, the calibrated N wave was used to display the mis-distance (unlike the RMDI), in actual feet.
My fellow lab mates of the time included Rodney Davis, the supervisor, Rick Sayer, Peter Dawson, Roger Giles Mick Howe and Nigel Barnes. The mis-distance indicators needed a lot of field trials work and that's when my earliest days travelling on behalf of the company, started and the system was trialled at ranges in Norfolk, South Wales, but best of all, Benbecula in the Outer Hebrides. I remember being there on a sunny midsummers day when it was light at midnight. I thought 'this is the life!'
AMDI had a third variant, the Air-to-Ground Scorer. This was a variant of the acoustic system for scoring the accuracy of aircraft firing at ground targets. The microphone was fitted to a conical target, deployed on mud flats on the shore. Calibration was by having a Hessian screen behind the target to show the distance by a hole count. There were a few nervous seagulls about!
AMDI and RMDI needed a lot of environmental testing a new Bruel & Kjaer vibrator facility had earlier been installed to test the weather radar, but we used it to shake the living daylights out of the MDI's. I spent many hours, sometimes overnight, watching and waiting for AMDI to fall to bits. It rarely did!
With the system going into small scale production, and with the new BS5750 quality standard looming, I was offered the job of Quality Manager and took the division through the necessary procedures, working for Tim Davis. As Quality Manager, I found myself involved with the industrial side too, and visited customer's plants both in the UK and in places with much better grub, in France, Holland and Denmark.
Groups of three or four of us used to visit French crane manufacturer PPM who were a major user of the crane safe–load indicator. Our visits were sales based, but with my quality hat on went along to have my ears bent about, shall we say, production problems!
We often got there in the final days of Ekco having its' own aeroplane. The original green Anson India Hotel, (shown on film in another part of the web site) had been replaced with Papa Golf, formerly AVRO's own corporate aircraft. On one occasion, there was Bill Thompson, Roy Barrett, Derek Hutchins, and myself hanging on for grim death while John Meredith the company's pilot dragged us into the air on a trip to Coles Cranes in Sunderland. The dear old Anson with its bulbous nose, modified to carry the weather radar, had a top speed more or less the same as a strong northerly coming down from Norway! It was a roller-coaster ride and trips in the Anson were always a bit on the slow side!
