spec - Local Sector 7 web page

Whenever the move_all command is used, it is important that the A[] array containthe current motor positions for all motors except the ones to be moved. In the aboveexample, the getangles command loads A[] with the current positions after thewaitmove ensures all motors have stopped. The calcA changes the appropriate elementsof the A[] array and the move_all starts the motors.Often, you might change a single angle, or several angles, and then wonder where inreciprocal space the diffractometer is set. The calcHKL macro will take the positionsin the A[] array and set the variables H , K ,and L to the calculated coordinates. Forexample:64.FOURC> waitmove; getangles; calcHKL; print H, K, L1 0 065.FOURC>The command getangles loads the A[] array with the current positions.CountingAnother important function of the diffractometer program is to measure the scatteredX-ray intensities. spec supports several types of timers, scalers and multichannelanalyzers (MCAs). Timers control the count time. Scalers count detected photons.MCAs accumulate many channels of counts and are used with energy-dispersivedetectors and positional-sensitive detectors.To count the number of X rays incident on the detector per second, the counting hardwaremust be able to accumulate detector counts accurately within a fixed timeperiod. The scaler hardware is gated by a clock that operates independently of thecomputer. Thus, the response time of the computer to interrupts (real-time events)does not affect the accuracy of the count. spec programs and starts the clock andsenses when the clock period, and hence the counting, has ended. spec can thenread the contents of the scalers and save the measurement in a data file.Clearing the scalers and starting the clock is accomplished by the functiontcount(seconds) .Tocount for one second, type:65.FOURC> tcount(1)66.FOURC>The contents of the scalers are accessed through the built-in S[] array. The hardwarescalers are read and their contents loaded into the scaler array by the getcountscommand. A second, associated string array, S_NA[] ,isdefined in the standardmacros and identifies each scaler:32 USER MANUAL AND TUTORIALS INTERIM WORK-IN-PROGRESS (8/16/01) NOT FOR GENERAL DISTRIBUTION