A Signal Averaging Program for an Interfaced Programmable Calculator Programmable calculators provide a unique opportunity to promptly perform calculations directly in the undergraduate lahoratory which previousp required the use of a digital computer. Another feature of some calculators (e.g., Wang 600 series) is their capacity to he interfaced to instruments and, hence, provide direct on-line input of digital information. A good demonstration of one of the advantages of interfacing which we presently use in the undergraduate physical chemistry lahoratory is that of signal averaging for signals with a poor signal-to-noise (random) ratio. A signal averaging program has been written for the Wang 600-6 calculator equipped with the printer and tape cassette option. Analog voltages are digitized (BCD) using a Digitec 252 digital voltmeter (DVM) and interfaced to the calculator using the Wang 605.1 interface.l The program is divided into two parts: (1)input of data from the DVM via the interface followed by storage on magnetic tape (cassette) and (2) recall of the data from the tape followed by a calculation of the mean and standard deviation. The sampling rate is limited by the maximum sending rate of the DVM and the receiving and processing (decimal point and sign assignment) rate of the interface-calculator combination. In our case, the sending rate of the DVM, 10 sec-1: is the limiting factor (receivingprocessing rate -100 sec-l). Under program control, the floating dec~malpoint is located and sign determined, the data point stored in hard storage, and, finally, transferred to soft storage (cassette) in ten blocks of ten points each. The required time for this process is =30 sec.Z Maximum continuous storage (i.e., on one side) on the standard length of cassette tape (Wang Lab. Inc.) is 1000 data points? In the second part of the program, the data hlocks are recalled one at a time, directly averaged, and stored in hard core. After the ten hlocks are recalled and averaged, the mean and standard deviation are calculated for the ten sub-populations. Copies of the program are available upon request. 1 Minor
program adjustments must he made for a DVM providing more or less digits. Approximately 20 sec of this time is dead time required for transfer from memory to tape. 3It is possihle to store even more data points if larger hlocks of numhers are stored in the core before transfer. 2
Edgar Watson, Jr. Joseph Krasowski Saint Joseph's College Philadelphia, Pennsylvania 19131
364 /Journal of Chemical Education
